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Author(s): Xiaohan Wang, Richard W. Tsien Author Affiliations: Suspect that modulates the heartbeat is ensnared In the Sherlock Holmes tale The Adventure of the Dancing Men , the detective runs [...], The activity of calcium channels in the heart increases during what is called the fight-or-flight response. An investigation into the 50-year-old mystery of how this occurs has captured a previously overlooked suspect. Protein kinase A targets Rad protein to boost calcium-channel activity.

Hypertension is a major public health problem and contributes to deaths from stroke, myocardial infarction and kidney failure. The prevalence of hypertension is high in populations with a high dietary [...], How high salt intake increases blood pressure is a key question in the study of hypertension. Salt intake induces increased renal sympathetic activity resulting in sodium retention. However, the mechanisms underlying the sympathetic control of renal sodium excretion remain unclear. In this study, we found that [β.sub.2]-adrenergic receptor (b2AR) stimulation led to decreased transcription of the gene encoding WNK4, a regulator of sodium reabsorption. [β.sub.2]AR stimulation resulted in cyclic AMP-dependent inhibition of histone deacetylase-8 (HDAC8) activity and increased histone acetylation, leading to binding of the glucocorticoid receptor to a negative glucocorticoid-responsive element in the promoter region. In rat models of salt-sensitive hypertension and sympathetic overactivity, salt loading suppressed renal WNK4 expression, activated the [Na.sup.+]-[Cl.sup.-] cotransporter and induced salt-dependent hypertension. These findings implicate the epigenetic modulation of WNK4 transcription in the development of salt-sensitive hypertension. The renal [β.sub.2]AR-WNK4 pathway may be a therapeutic target for salt-sensitive hypertension.

Dietary methionine restriction (MR) limits fat deposition and decreases plasma leptin, while increasing food consumption, total energy expenditure (EE), plasma adiponectin, and expression of uncoupling protein 1 (UCP1) in brown and white adipose tissue (BAT and WAT). [beta]adrenergic receptors ([beta] ]AR) serve as conduits for sympathetic input to adipose tissue, but their role in mediating the effects of MR on energy homeostasis is unclear. Energy intake, weight, and adiposity were modestly higher in [[beta].sub.3][AR.sup. ]/mice on the Control diet compared with wild ]]type (WT) mice, but the hyperphagic response to the MR diet and the reduction in fat deposition did not differ between the genotypes. The absence of [[beta].sub.3]ARs also did not diminish the ability of MR to increase total EE and plasma adiponectin or decrease leptin mRNA, but it did block the MR ]dependent increase in UCP1 mRNA in BAT but not WAT. In a further study, propranolol was used to antagonize remaining [beta]adrenergic input ([[beta].sub.1] and [[beta].sub.2]ARs) in [[beta].sub.3][AR.sup./] mice, and this treatment blocked >50% of the MR ]induced increase in total EE and UCP1 induction in both BAT and WAT. We conclude that signaling through [beta]adrenergic receptors is a component of the mechanism used by dietary MR to increase EE, and that [[beta].sub.1] and [[beta].sub.2]ARs are able to substitute for [[beta].sub.3] ]ARs in mediating the effect of dietary MR on EE. These findings are consistent with the involvement of both UCP1 dependent and]independent mechanisms in the physiological re sponses affecting energy balance that are produced by dietary MR. energy expenditure; metabolic efficiency; futile cycles; adipose tissue; dietary restriction; leptin; adiponectin; oxidative metabolism; uncoupling doi: 10.1152/ajpregu.00838.2009.

We recently observed the enhanced serine and matrix metalloproteinase (MMP) activity in the spontaneously hypertensive rat (SHR) compared with its normotensive Wistar-Kyoto (WKY) rat and the cleavage of membrane receptors in the SHR by MMPs. We demonstrate in vivo that MMP-7 and MMP-9 injection leads to a vasoconstrictor response in microvessels of rats that is blocked by a specific MMP inhibitor (GM-6001, 1 [micro]M). Multiple pathways may be responsible. Since the [[beta].sub.2]-adrenergic receptor ([[beta].sub.2]-AR) is susceptible to the action of endogenous MMPs, we hypothesize that MMPs in the plasma of SHRs are able to cleave the extracellular domain of the [[beta].sub.2]-AR. SHR arterioles respond in an attenuated fashion to [[beta].sub.2]-AR agonists and antagonists. Aorta and heart muscle of control Wistar rats were exposed for 24 h (37[degrees]C) to fresh plasma of male Wistar and WKY rats and SHRs with and without doxycycline (30 [micro]M) and EDTA (10 mM) to reduce MMP activity. The density of extracellular and intracellular domains of [[beta].sub.2]-AR was determined by immunohistochemistry. The density of the extracellular domain of [[beta].sub.2]-AR is reduced in aortic endothelial cells and cardiac microvessels of SHRs compared with that of WKY or Wistar rats. Treatment of the aorta and the heart of control Wistar rats with plasma from SHRs, hut not from WKY rats, reduced the number of extracellular domains, but not intracellular domains, of [[beta].sub.2]-AR in aortic endothelial cells and cardiac microvessels. MMP inhibitors (EDTA and doxycycline) prevented the cleavage of the extracellular domain. Thus MMPs may contribute to the reduced density of the extracellular domain of [[beta].sub.2]-AR in blood vessels and to the increased arteriolar tone of SHRs compared with normotensive rats. receptor cleavage; cardiac microvessels; aorta; arterioles doi: 10.1152/ajpheart.00620.2009.

The alveolar epithelium plays a critical role in resolving pulmonary edema. We thus hypothesized that its function might be upregulated in rats with heart failure, a condition that severely challenges the lung's ability to maintain fluid balance. Heart failure was induced by left coronary artery ligation. Echocardiographic and cardiovascular hemodynamics confirmed its development at 16 wk postligation. At that time, alveolar fluid clearance was measured by an increase in protein concentration over 1 h of a 5% albumin solution instilled into the lungs. Baseline alveolar fluid clearance was similar in heart failure and age-matched control rats. Terbutaline was added to the instillate to determine whether heart failure rats responded to [beta]-adrenoceptor stimulation. Alveolar fluid clearance in heart failure rats was increased by 194% after terbutaline stimulation compared with a 153% increase by terbutaline in control rats. To determine the mechanisms responsible for this accelerated alveolar fluid clearance, we measured ion transporter expression (ENaC, Na-KATPase, CFTR). No significant upregulation was observed for these ion transporters in the heart failure rats. Lung morphology showed significant alveolar epithelial type II cell hyperplasia in heart failure rats. Thus, alveolar epithelial type II cell hyperplasia is the likely explanation for the increased terbutaline-stimulated alveolar fluid clearance in heart failure rats. These data provide evidence for previously unrecognized mechanisms that can protect against or hasten resolution of alveolar edema in heart failure. albumin; terbutaline

There is abundant literature on the role of the basolateral amygdala (BLA) and the CA1 region of the hippocampus in memory formation of inhibitory avoidance (IA) and other behaviorally arousing tasks. Here, we investigate molecular correlates of IA consolidation in the two structures and their relation to NMDA receptors (NMDArs) and [beta]-adrenergic receptors ([beta]-ADrs). The separate posttraining administration of antagonists of NMDAr and [beta]-ADr to BLA and CA1 is amnesic. IA training is followed by an increase of the phosphorylation of calcium and calmodulin-dependent protein kinase II (CaMKII) and ERK2 in CA1 but only an increase of the phosphorylation of ERK2 in BLA. The changes are blocked by NMDAr antagonists but not [beta]-ADr antagonists in CA1, and they are blocked by [beta]-ADr but not NMDAr antagonists in BLA. In addition, the changes are accompanied by increased phosphorylation of tyrosine hydroxylase in BLA but not in CA1, suggesting that [beta]-AD modulation results from local catecholamine synthesis in the former but not in the latter structure. NMDAr blockers in CA1 do not alter the learning-induced neurochemical changes in BLA, and [beta]-ADr blockade in BLA does not hinder those in CA1. When put together with other data from the literature, the present findings suggest that CA1 and BLA play a role in consolidation, but they operate to an extent in parallel, suggesting that each is probably involved with different aspects of the task studied. consolidation | inhibitory avoidance | learning

Regulation of vascular tone and blood flow involves interactions between numerous local and systemic vascular control signals, many of which are altered by Type 2 diabetes (T2D). Vascular responses to endothelin-1 (ET-1) are mediated by endothelin type A (ETA) and type B ([ET.sub.B]) receptors that have been implicated in cross talk with [[alpha].sub.1]-adrenoceptors ([[alpha].sub.1]-AR). [ET.sub.A] and [ET.sub.B] receptor expression and plasma ET-1 levels are elevated in T2D; however, whether this influences coronary [[alpha].sub.1]-AR function has not been examined. Therefore, we examined the effect of [ET.sub.A] and [ET.sub.B] receptor inhibition on coronary vasoconstriction to ET-1 and [[alpha].sub.1]-AR activation in a mouse model of T2D. Coronary vascular responses were examined in isolated mouse hearts from control and diet-induced T2D C57BL/6J mice. Responses to ET-1 and the selective [[alpha].sub.1]-AR agonist phenylephrine (PE) were examined alone and in the presence of the nitric oxide synthase inhibitor [N.sup.[omega]]-nitro-L-arginine methyl ester (L-NAME) alone or in combination with selective [ET.sub.A] or [ET.sub.B] receptor inhibitors BQ-123 and BQ-788, respectively. Vasoconstriction to ET-l was enhanced, whereas [ET.sub.B], but not [ET.sub.A], receptor blockade reduced basal coronary tone in T2D hearts. In the presence of L-NAME, [ET.sub.A] receptor inhibition attenuated ET-1 vasoconstriction in both groups, whereas [ET.sub.B] inhibition abolished this response only in control hearts. In addition, [ET.sub.A] inhibition enhanced [[alpha].sub.1]-AR-mediated vasoconstriction in T2D, but not control, hearts following L-NAME treatment. Therefore, in this model, enhanced coronary ET-1 responsiveness is mediated primarily through smooth muscle [ET.sub.B] receptors, whereas the interaction with [[alpha].sub.1]-ARs is mediated solely through the [ET.sub.A] receptor subtype. isolated heart; C57BL/6J mouse; diet-induced diabetes

Background. There is little information regarding the effects of strength training on intermuscular fat (IMF). This study examines changes in IMF in response to strength training in carriers of the adrenergic receptor (ADR) [Beta]2Glu27 polymorphism versus noncarriers and between carriers of ADR[Alpha]2b [Glu.sup.9] polymorphism versus noncarriers. Methods. Midthigh IMF and muscle area were measured by computed tomography (CT) before and after 10 weeks of single-leg strength training in healthy, sedentary middle-aged and older (50-83 years) men ([Eta] = 46) and women ([Eta] = 52) in both their trained and untrained (control) legs. Results. The strength training program resulted in a substantial increase in one-repetition maximum strength (p < .001) and muscle area (p < .001), but no significant changes in IMF in the whole group. However, IMF was significantly reduced with strength training in participants carrying ADR[Beta]2 Glu27 (-2. 3 [+ or -] 1.0 [cm.sup.2], p = .028), but no significant change was observed with ADR[Beta]2 Glu27 noncarriers. The decrease in IMF in ADR[Alpha]2b [Glu.sup.9] carriers (-1.9 [+ or -] 1.0 [cm.sup.2], p = .066) was significantly different (-2.9 [+ or -] 1.5 [cm.sup.2], p - .043) from a nonsignificant increase in ADR[Alpha]2b [Glu.sup.9] noncarriers. ADR[Beta] Glu27 carriers who also carried ADR[Alpha]2b [Glu.sup.9] significantly lost IMF with strength training (-3.8 [+ or -] 1.5 [cm.sup.2], p = .018). Conclusion. ADR genotype influences IMF response to strength training.

Stimulation of [beta]-adrenoceptors contributes to the relaxation of urinary bladder smooth muscle (UBSM) through activation of large-conductance [Ca.sup.2+]-activated [K.sup.+] (BK) channels. We examined the mechanisms by which [beta]-adrenoceptor stimulation leads to an elevation of the activity of BK channels in UBSM. Depolarization from -70 to +10 mV evokes an inward L-type dihydropyridine-sensitive voltage-dependent [Ca.sup.2+] channel (VDCC) current, followed by outward steady-state and transient BK current. In the presence of ryanodine, which blocks the transient BK currents, isoproterenol, a nonselective [beta]-adrenoceptor agonist, increased the VDCC current by ~25% and the steady-state BK current by ~30%. In the presence of the BK channel inhibitor iberiotoxin, isoproterenol did not cause activation of the remaining steady-state [K.sup.+] current component. Decreasing [Ca.sup.2+] influx through VDCC by nifedipine or depolarization to +80 mV suppressed the isoproterenol-induced activation of the steady-state BK current. Unlike forskolin, isoproterenol did not change significantly the open probability of single BK channels in the absence of [Ca.sup.2+] sparks and with VDCC inhibited by nifedipine. Isoproterenol elevated [Ca.sup.2+] spark (local intracellular [Ca.sup.2+] release through ryanodine receptors of the sarcoplasmic reticulum) frequency and associated transient BK currents by ~1.4-fold. The data support the concept that in UBSM [beta]-adrenoceptor stimulation activates BK channels by elevating [Ca.sup.2+] influx through VDCC and by increasing [Ca.sup.2+] sparks, but not through a [Ca.sup.2+]-independent mechanism. This study reveals key regulatory molecular and cellular mechanisms of [beta]-adrenergic regulation of BK channels in UBSM that could provide new targets liar drugs in the treatment of bladder dysfunction. [Ca.sup.2+] sparks; voltage-dependent [Ca.sup.2+] channel; ryanodine receptor

[beta]-Adrenoceptor stimulation serves as the most powerful means to increase cardiac output in response to stress or exercise. However, sustained [beta]-adrenoceptor stimulation promotes pathological cardiac remodeling such as myocyte hypertrophy and apoptosis, thus contributing to heart failure. Coexisting cardiac [beta]-adrenoceptor subtypes, mainly [[beta].sub.1]-adrenoceptors and [[beta].sub.2]-adrenoceptors, activate different signaling cascades with [[beta].sub.1]-adrenoceptors coupling to [G.sub.s] and [[beta].sub.2]-adrenoceptors coupling to [G.sub.s] and [G.sub.i] pathways. As a result, sustained [[beta].sub.2]-adrenoceptor stimulation protects cardiomyocytes against apoptosis via a [G.sub.i] phosphatidylinositol 3-kinase--protein kinase B pathway, whereas chronic [[beta].sub.1]-adrenoceptor stimulation induces myocyte hypertrophy and apoptosis by protein kinase A-independent activation of calmodulin kinase II signaling. These advances in our understanding of [beta]-adrenoceptor subtype signaling identify the mechanisms that underlie the beneficial effects of [beta]-adrenoceptor antagonists and delineate the rationale for combining [[beta].sub.1]-adrenoceptor blockade with [[beta].sub.2]-adrenoceptor activation as a potential therapy for heart failure.

[beta]-Adrenoceptors ([beta]-ARs) are seven-transmembrane domain, G proteincoupled receptors that transduce the cellular effects of epinephrine and norepinephrine and play a pivotal role in the vertebrate stress response. This study reports the cloning and characterization of two previously unreported [beta]-ARs from the rainbow trout (Oncorhynchus mykiss). Phylogenetic analysis of amino acid sequences indicates that both [beta]-ARs are homologs of the mammalian [[beta].sub.3]-AR. Analysis of tissue expression patterns indicates that one of these trout [[beta].sub.3]-adrenoceptors ([[beta].sub.3a]-AR) is highly expressed in gill and heart, whereas the second ([[beta].sub.3b]-AR) is highly expressed by red blood cells (RBC). Expression of the [[beta].sub.3b]-AR in the RBC coupled with the finding of a single category of [beta]-AR binding sites on RBC membranes provides strong evidence for the control of the trout RBC [beta]-AR [Na.sup.+]/[H.sup.+] exchanger ([beta]-NHE) activity by signaling through this [[beta].sub.3b]-subtype and not through a [[beta].sub.1]-subtype as previously proposed. The RBC-specific trout [[beta].sub.3b]-AR exhibits binding characteristics that distinguish this receptor from each of the three pharmacologically defined categories of mammalian [beta]-ARs ([[beta].sub.1]-, [[beta].sub.2]-, and [[beta].sub.3]-AR). This study is the first to report the presence of a [[beta].sub.3]-AR subtype in a fish species, and the proposal that the [[beta].sub.3b]-AR controls RBC [beta]-NHE activity represents a novel role for the [[beta].sub.3]-AR subtype in vertebrates. molecular sequence; tissue expression; evolutionary analysis; binding kinetics; [beta]-adrenoceptors

The possible involvement of different kinases in the [[alpha].sub.1]-adrenoreceptor (AR)-mediated positive inotropic effect (PIE) was investigated in rat papillary muscle and compared with [beta]-AR-, endothelin receptor- and phorbol ester-induced changes in contractility. The [[alpha].sub.1]-AR-induced PIE was not reduced by the inhibitors of protein kinase C (PKC), MAPK (ERK and p38), phosphatidyl inositol 3-kinase, or calmodulin kinase II. However, PKC inhibition attenuated the effect of phorbol 12myristate 13-acetate (PMA) on contractility. [[alpha].sub.1]-AR-induced PIE was reduced by ~90% during inhibition of myosin light chain kinase (MLCK) by 1-(5-chloronaphthalene-1-sulfonyl)1H-hexahydro-1,4-diazepine (ML-9). Endothelin-induced PIE was also reduced by ML-9, but ML-9 had no effect on [beta]-AR-induced PIE. The Rho kinase inhibitor Y-27632 also reduced the [[alpha].sub.1]-AR-induced PIE. The [[alpha].sub.1]-AR-induced PIE in muscle strips from explanted failing human hearts was also sensitive to MLCK inhibition. [[alpha].sub.1]-AR induced a modest increase in [.sup.32]P incorporation into myosin light chain in isolated rat cardiomyocytes. This effect was eliminated by ML-9. The PIE of [[alpha].sub.1]-AR stimulation seems to be dependent on MLCK phosphorylation. endothelin; inhibitors; l-(5-chloronaphthalene-l-sulfonyl)1H-hexahydro-l,4-diazepine; phenylephrine; Rho kinase; [alpha]-adrenoreceptor

In the rat proximal tubule, the [[alpha].sub.2B]-adrenergic receptor ([[alpha].sub.2B]-AR) enhances [Na.sup.+] reabsorption by increasing the activity of [Na.sup.+]/[H.sup.+] exchanger isoform NHE3. The mechanisms involved are unclear, and inhibition of cAMP production remains controversial. In this study, we reinvestigated [[alpha].sub.2B]-AR signaling pathways using rat proximal tubule cells (PTC) in primary culture and LLC-P[K.sub.1] cells permanently transfected with the RNG gene (rat nonglycosylated [[alpha].sub.2]-AR). Binding experiments indicated that PTC express substantial amounts of [[alpha].sub.2B]-AR (130 fmol/mg protein), and only RNG transcripts were detected. In both cell types, the [[alpha].sub.2B]-AR is coupled to G protein, and its stimulation by dexmedetomidine, but not by UK-14304, provoked a significant inhibition of the accumulation of cAMP induced by. forskolin or parathyroid hormone. Exposure to [[alpha].sub.2]-agonists increased arachidonic acid release and caused extracellular signal-regulated kinase (ERK)1/2 phosphorylation, which correlated with enhanced mitogen-activated protein kinse (MAPK) activity and nuclear translocation. MAPK phosphorylation was blunted by pertussis toxin but not by protein kinase C desensitization, and it coincided with transient phosphorylation of Shc. Finally, treatment with UK-14304 accelerated cell growth. Further studies will be necessary to clarify the precise mechanism of MAPK activation, but the present data suggest that [[alpha].sub.2B]-AR may play a positive role during tubular regeneration. kidney; mitogen-activated protein kinase

Auman, J. T., F. J. Seidler, C. A. Tate, and T. A. Slotkin. [beta]-Adrenoceptor-mediated cell signaling in the neonatal heart and liver: responses to terbutaline. Am J Physiol Regulatory Integrative Comp Physiol 281: R1895-R1901, 2001.--Terbutaline, a [[beta].sub.2]-adrenoceptor ([[beta].sub.2]-AR) agonist, is a widely used tocolytic that also crosses the placenta to stimulate fetal [beta]-ARs. The current study examines the effects of terbutaline administered to neonatal rats. Terbutaline (10 mg/kg sc) given on postnatal day (PN) 2-5 or PN 11-14 elicited significant downregulation of both cardiac and hepatic [beta]-ARs, with a much greater effect in the liver. Despite the reduction in cardiac [beta]-ARs, receptor desensitization was absent as evidenced by the maintained ability of isoproterenol to stimulate adenylyl cyclase (AC) in membrane preparations. The underlying mechanism was dissected by using stimulants that operate at different points in the AC signaling pathway, NaF, forskolin, and [Mn.sup.2+]. When administered in the early neonatal period, terbutaline failed to evoke any changes in cardiac AC activity; however, treatment on PN 11-14 evoked heterologous sensitization downstream from the receptor, evidenced by increases in the response to NaF and forskolin. In the liver, neonatal terbutaline administration elicited a small ([approximately equal to] 10%) decrease in the AC response to isoproterenol, an effect much smaller than the downregulation of [beta]-ARs (>40%). In this tissue, desensitization was again offset by heterologous sensitization of AC signaling. These results indicate that, in the developing organism, [beta]-AR-mediated cell signaling responses are maintained in the face of receptor downregulation through heterologous induction of downstream signaling elements. These unique responses serve to sustain [beta]-AR signaling in the perinatal period. adenylyl cyclase; liver; [beta]-adrenoceptor; preterm labor; adenosine 3',5'-cyclic monophosphate; terbutaline; development; tocolysis; heart Received 18 June 2001; accepted in final form 23 August 2001

The (beta)-adrenergic receptors ((Beta)AR) on the surface of mammalian cells are desensitized when the cell is stimulated by (Beta)AR agonists to eliminate excessive response by the cell. Investigations with adipocytes, primarily rodent-derived cells, indicate other hormones and substrates also can modulate the individual (Beta)AR subtypes. For example, glucocorticoids decrease the (Beta)1AR and the (Beta)3AR but increase the (Beta)2AR. Insulin decreases the (Beta)3AR. Thyroid hormones increase the (Beta)3AR and butyrate increases (Beta)1AR and (Beta)2AR but dramatically decreases (Beta)3AR. Because porcine adipocytes have unique functional and ligand-binding properties compared to rodent adipocytes and because porcine adipocytes contain predominantly (Beta)1AR, compared to rodent adipocytes with predominantly (Beta)3AR, we expect the regulation of porcine adipocyte (Beta)AR by hormones and substrates to be different from that in rodent adipocytes. Isolated porcine adipocytes were incubated for 6 and 21 h without and with dexamethasone, insulin, triiodothyronine, or butyrate. Cells incubated without hormone or butyrate had a decreased (Beta)AR number at 21 h. The (Beta)1AR and (Beta)2AR transcript concentrations were decreased after 6 h and tended to rebound after 21 h of incubation. Dexamethasone did not change the total (Beta)AR number but tended to increase the (Beta)1AR and (Beta)2AR transcript concentrations. Insulin increased the (Beta)AR number and decreased both transcript concentrations at 21 h. Triiodothyronine and butyrate did not change the receptor number or transcript concentrations. The results indicate that (Beta)AR transcript concentrations do not accurately predict the (Beta)AR protein concentration (estimated by ligand binding). Results also indicate that (Beta)AR in porcine adipocytes are relatively unresponsive to hormones and butyrate compared to rodent-derived adipocytes described in the literature. Key Words: Receptors, Pigs, Adipose Tissues, Glucocorticoids, Insulin, Thyroid Hormones, Butyrates

Research was conducted to determine whether norepinephrine (NE) and other hormonal factors have direct effects on protein degradation in brown fat cells. NE was observed to inhibit proteolysis by 35-45% in mouse brown adipocytes differentiated in culture. Insulin also inhibited protein degradation but much less than NE, while glucagon and leptin had no effect. Results showed that inhibition of proteolysis by NE and insulin in mature brown adipocytes is likely an essential process involved in brown fat growth and atrophy.

Primary brown adipocyte cultures were employed to determine the role of beta-adrenergic receptor (beta-AR) subtypes in mediating lipolysis and uncoupling protein-1 gene expression, elicited by the physiological neurohormone norepinephrine (NE). Findings indicated that beta-AR subtypes regulate various physiological responses stimulated by NE in brown adipocyte cultures in part by differentially transducing signals to subcellular compartments.

The consequences of the cAMP pathway on the Ca2+ response evoked by the phospholipase C-coupled receptor stimulations were examined in rat parotid cells. Even though 1 microM isoproterenol (Iso) had no effect on the cytosolic Ca2+ concentration, the pretreatment with Iso potentiated Ca2+ responses elicited by phenylephrine. The potentiating effect of Iso was caused by a shifting of the concentration-response curves of phenylephrine to the left and an increase in the maximal response.

The phosphorylation of Ser(super 16) and Thr(super 17) of phospholamban (PLB) due to the beta-adrenergic regulation of cardiac relaxation of perfused rat hearts has been studied using antibodies recognizing PLB at either position. PLB controls the affinity of cardiac sarcoplasmic reticulum Ca2+-ATPase for Ca2+ while Ser(super 16) and Thr(super 17) are amino acid residues. Results indicate that the phosphorylation of PLB at Ser(super 16) is preferentially involved in the acceleration of cardiac relaxation after beta-adrenergic stimulation.

Neither the glucocorticoid receptor gene (GRL) nor the beta2-adrenergic receptor gene (ADRB2) play a role in physiological variation of blood pressure and body mass index. In a linkage analysis of chromosome 5q31-5q32 in relation to the physiological variation in blood pressure, body mass index and related phenotypes, it was found that genetic similarity was not associated with phenotypic similarity for systolic and diastolic blood pressure, body mass index, weight, height or pulse rate at any loci.

The relationship between a low rate of fat oxidation and low lipolytic response to beta-adrenergic stimulation was investigated by measuring the lipolytic response to isoproterenol and whole body fat oxidation in 21 males. Results showed that a low lipolytic response to isoproterenol in subcutaneous adipose tissue was linked to a low rate of fat oxidation indicating that weight gain may be influenced by low lipolytic response to beta-adrenoreceptor stimulation.

The role of the beta adrenergic system on the modulation of plasma triglyceride levels after cold exposure was investigated using beta adrenergic receptor blocking studies with propranolol. Results reveal that triglyceride secretion increased after cold exposure and this was blunted by propranolol. Further, despite the increase in triglyceride secretion, its serum level dropped indicating that it is hydrolyzed intravascularly.

The reduced response to beta-adrenoceptor stimulation in diabetic hearts was investigated in enzymatically isolated diabetic rat ventricular myocytes in contrast with age-matched controls. Findings showed that diabetes damages the contractile and (Ca(super 2+))(sub i) responses of cardiac myocytes when stimulated at both beta-adrenoceptors and the postreceptor level without affecting the L-type Ca(super 2+) response. Also, the modified sarcoplasmic reticulum functions of uptake and/or release of Ca(super 2+) is possibly a major contributor to the reduced beta-adrenergic response.

Corticosteroid hormones increase the density of [Beta]-adrenoceptors in some tissues and may be able to prevent the anabolic effects of [Beta]-agonists from becoming attenuated. The aim of this study was to find a suitable dose of corticosterone that would up-regulate [[Beta].sub.2]-adrenoceptors in skeletal muscle without arresting the animal's growth. Male rats were given five daily injections of corticosterone at 0, 6.25, 12.5, 25, or 50 mg/kg. The animals were far more sensitive to the catabolic effects of this steroid than female rats used in a previous study. There was no change in food intake, liver, heart, or soleus muscle mass, but corticosterone caused a dose-related decrease in weight gain, carcass weight, omental fat pad weight, and gastrocmemius/plantaris muscle mass (P < .01). From a regression of muscle mass against dose, we calculated that 4.4 mg[multiplied by][kg.sup.-1][multiplied by][d.sup.-1] would be the largest dose of corticosterone that a male rat could tolerate without any catabolic effect in skeletal muscle. Corticosterone failed to increase [Beta]-adrenoceptor density at any of the doses tested. We conclude that corticosterone treatment is unlikely to be effective at enhancing the growth response of male rats to [Beta]-agonists. Key Words: [Beta]-Adrenergic Receptors, Skeletal Muscle, Clenbuterol, Corticosterone, Rats, Growth

The influence of phosphorylation on the localization of beta-adrenergic receptors during sepsis was investigated using a rat model. Results reveal that sepsis brings about an early hypercardiodynamic state followed by a hypocardiodynamic state. Initially, there is concentration of receptors at the sarcolemma followed by a relocalization of these receptors in light vesicles. This relocalization is correlated with receptor phosphorylation.

The effects of beta2-adrenergic receptors on the regulation of intracellular calcium and calcium flux across rat ventricular myocytes were investigated using receptor agonist and antagonist as well as blocking experiments directed at possible signal transduction mechanisms. Results reveal that beta2-adrenergic receptors do not have a role in calcium homeostasis in the myocardium of adult rats.

Beta1-adrenoceptors are important components of the sympathetic control of heart rate. The significance of this class of receptors on the resting heart rate and cardiovascular performance during exercise is investigated using mutant mice that do not express this receptor. Results reveal that maintaining the resting heart rate and the maximal cardiovascular performance during exercise does not require beta1-adrenoceptors.

The oxygen consumption response of isolated senescent brown adipocyte to stimulation with norepinephrine and one of its agonists was measured to determine the influence of senescence on beta adrenergic responsiveness in adipocytes. Results reveal that senescent adipocytes consume 51% to 60% less oxygen on maximal beta stimulation. On the other hand, chronological age does not significantly alter beta receptor mediated thermogenesis in brown adipocyte.

Bovine tracheal epithelial cells were used in the investigation of the effect of tannin on the airway epithelium. Tannin was shown to inhibit the effects of the beta agonist isoproterenol. The desensitization is dose and time dependent but reversible. Tannin was also shown to diminish beta adrenergic receptor density and cause the dissociation of the receptor from the stimulatory G protein. The length of the tannin polyner and its interaction with cysteine residues modulate these effects.

The density of the beta adrenergic receptors in the heart and their binding affinity and the expression of stress protein 70 were investigated in rainbow trouts exposed to oxygen-poor water. Results indicate that the hearts of salmonid fishes are well adapted to hypoxia and are able to perform well even in oxygen-poor conditions. The expression of beta adrenergic receptors on the myocardium exhibits a degree of plasticity subject to environmental conditions.

Hydrogen peroxide, a substance containing an activated oxygen species, depresses both the density of both beta1 and beta2 adrenergic receptors and the affinity of beta1 receptors in isolated membranes from rat muscles. The effect of H2O2 on various enzymes in the signal transduction pathway was also investigated using enzyme inhibition assays. Results indicate that hydrogen peroxide disrupts the activity of stimulatory G proteins and the catalytic subunit of adenylyl cyclase thus inhibiting beta receptor signal transduction.

Ten sedentary older men were made to undergo exercise training for nine months which increased their aerobic capacity by 28%. Training enhanced cardiac inotropic responses as assessed by two-dimensional echocardiography. The beneficial effects of exercise on cardiac contraction were negated with esmolol beta adrenergic blockade indicating that the increased in cardiac contractility is brought about by increased sensitivity to catecholamines.

During the first few weeks after birth, major changes occur in porcine adipocyte lipid metabolism. Two of the important receptors controlling lipid metabolism in adipocytes are the [Beta]-adrenergic receptors ([Beta]AR) and the [A.sub.1] adenosine receptors ([A.sub.1]R). To gain insight into the role of these receptors in modulating neonatal adipocyte lipid metabolism, we measured receptor affinity and number in suckling pigs. Adipose tissue from crossbred (X-Bred) and genetically obese suckling pigs at 0, 3, 10, and 17 d of age was used to prepare crude membranes. The [Beta]AR and [A.sub.1]R number and affinity were measured in membranes by equilibrium saturation binding with radioligands. Obese pigs were smaller than X-Bred pigs (average weight = 1.62 and 2.43 kg for obese and X-Bred, respectively; P < .01). Osmium-fixed adipocytes were larger in obese pigs than in X-Bred pigs (average cell diameter = 34.4 and 30.1 [[micro]meter] for obese and X-Bred, respectively; P < .01). In the obese and X-Bred pigs, the affinity of the [Beta]AR for iodocyanopindolol was greater (lower [K.sub.d]) at 17 d than at the younger ages (average [K.sub.d] = 177 pM at 17 d compared with > 330 pM at younger ages; age effect P < .01). The pattern for the [Beta]AR number was complex; the lowest receptor number was at 10 d of age in obese and X-Bred pigs (average number = 41 at 10 d compared with > 65 fmol/mg protein at older and younger ages; age effect P = .03). The higher [Beta]AR [K.sub.d] and the lower receptor number in younger animals suggest less regulation by physiologic concentrations of epinephrine and norepinephrine. This would allow greater anabolic lipid metabolism to proceed during the neonatal period, when adipocytes increase four- to sixfold in volume. There were no measurable AiR at any of these early ages; thus, adenosine control mechanisms to counteract the [Beta]AR and provide negative controls to lipid accretion are not operable in suckling pigs. Key Words: Neonatal Animals, Adipocytes, [Beta]-Adrenergic Receptors, Adenosine, Suckling, Obesity

An unusual case of Cushing's syndrome possibly caused by an abnormal proliferation of beta-adrenergic receptors in the adrenal glands is examined. In a 56-year-old man situations such as induced low blood sugar and stress that caused an increase in certain hormones, catecholamines, resulted in a corresponding increase in his cortisol levels. The adrenal tissue was found to have a high number of beta-adrenergic receptors, known to mediate the actions of catecholamines. The diagnosis was supported by the correction of the patient's cortisol levels with treatment with propranolol, a drug that blocks these receptors.

The effects of interleukin-1beta on the function of beta-adrenergic receptor adenylyl cyclase activity in human airway epithelial cells were investigated. Cultured BEAS-2B cells were used in an experiment to determine whether interleukin-1beta treatment alters cell number or viability. Results revealed that the effects of interleukin-1beta on beta-adrenergic receptor expression depend on time and dose. Also, interleukin-1beta induces changes in the expression and function of the beta-adrenergic receptor-adenylyl cyclase system of human airway epithelial cells.

The effects of chronic pretreatment with the cholinergic agonist carbachol on adenylyl cyclase, beta-adrenergic receptors and G protein functions in airway smooth muscle were investigated. Bovine tracheas were used in the experiment to determine the duration of carbachol pretreatment to reduce adenylyl cyclase activity. Results showed a decrease in basal and stimulated adenylyl cyclase activity when bovine airway smooth muscle was pretreated with the muscarinic agonist carbachol. All upstream stimulators were affected during the carbachol pretreatment process.

A study was conducted to determine the relationship between heart rate frequency and myocardial contractility. Another purpose was to investigate the effects of beta-adrenergic stimulation in the normal murine heart under open-chest conditions and intact heart recovering from anesthesia. Based on the findings of the study, there was an increased beta-adrenergic stimulation of the myocardium, sinus node and conduction system influence during the murine's recovery from anesthesia. Significance of the heart rate level was important in inotropic effect of beta-adrenergic stimulation.

The mechanisms that mediate the effects of muscarinic agonists on the actions of beta1- and beta2-adrenergic receptors were analyzed in neonatal rat ventricular myocytes. The administration of isotoproterenol enhanced inotropic and lusitropic vasorelaxation and increased the accumulation of cyclic adenosine 3',5'-monophosphate (cAMP). However, the inotropic and lusitropic effects of the beta-receptor agonist/beta2-receptor agonist was inhibited by carbachol via a mechanism that was mediated by M2-muscarinic receptor and a pertussis toxin-sensitive pathway.

The effects of prolonged isotoproterenol incubation of bronchial epithelial cells on the density of beta-adrenoceptors (betaAR) and betaAR protein degradation were analyzed in BEAS-2B cell lines. Maintained exposure of BEAS-2B cells to Iso, forskolin and dibutyryl adenosine 3',5'-cyclic monophosphate induced significant betaAR downregulation. However, incubation of BEAS-2B cells in Iso did not alter the basal levels of beta2AR messenger RNA.

The mechanisms that mediate the beta-adrenergic stimulation of gastric somatostatin and gastrin were characterized by utilizing beta-adrenoceptor (AR) agonists and antagonists such as SR-58611A and SR-59230A. Administration of SR-59611A beta-AR agonists stimulated the release of somatostatin and gastrin in isolated rat gastric antral epithelial cells in a concentration-dependent manner. However, the effects of SR-58611A were inhibited by the administration of the selective beta-AR antagonists such as SR-59230A and ICI-118551.

The effects of tumor necrosis factor (TNF)-alpha on beta-adrenergic receptor signal transduction during chronic airway inflammation was analyzed in cultured airway smooth muscle (ASM) cells. Cultured canine ASM cells exposed to TNF-alpha increased basal adenylate cyclase activity. TNF-alpha also impaired the ability of the beta-adrenergic receptor to stimulate adenylate cyclase indicating the role of beta-adrenergic receptor dysfunction in promoting chronic airway inflammation.

The role of beta-adrenergic stimulation on the splanchnic metabolic and circulatory effects of orally ingested glucose was analyzed in healthy human subjects after the administration of propranolol. Oral ingestion of glucose in propranolol-treated individuals promoted extrasplanchnic thermogenesis due to glucose-induced oxidative metabolism. On the other hand, beta2-receptor adrenergic stimulation promoted the physiological glucose-induced stimulation of splanchnic blood flow.

The left coronary artery of rats with myocardial infarction were analyzed to determine the status of the beta-adrenergic-adenylyl cyclase system in the left and right ventricle. Administration of isotoproterenol in rats with coronary artery occlusion reduced adenylyl cyclase activity and stimulated enzyme activity in the right ventricle. Alterations in the left and right ventricles were mediated by a decrease in the density of beta-adrenergic receptors and the degree of congestive heart failure.

The effects of delta-opioid peptide receptors (delta-OPR) in regulating the effects of beta-adrenergic receptor (beta-AR) stimulation on Ca2+ current were analyzed in individual rat cardiac ventricular cells. Administration of leucine enkephalin in single rodent cardiac myocytes reduced cellular response to beta-AR stimulation. Furthermore, delta-OPR activated a direct negative inotropic effect on beta-AR signaling in rodent heart cells.

The effects of norepinephrine (NE) on intraglomic sympathetic nerve endings and the mechanisms of alpha2-adrenoceptor mediated response to the neurotransmitter were analyzed in rabbit carotid body (CB) bifurcations. Analysis of in vitro rabbit CB preparations during hypoxic stimulation indicated the role of alpha2-adrenergic receptors in mediating the inhibitory activity of NE on carotid sinus nerve discharges. Furthermore, activation of alpha2-receptors also inhibited CB chemoreceptors.

The effects of adrenergic stimulation and adenosine 3',5' - cyclic monophosphate (cAMP) on Ba2+ currents (IBa), K+ contracture and Ca2+ channels were analyzed in frog slow-twitch skeletal muscles. Three-microelectrode voltage clamp analysis of frog skeletal muscles indicated the role of epinephrine in reducing the time course of IBa decay by increasing skeletal muscle Ca2+ current. Furthermore, external application of 8-BrcAMP analogue enhanced the amplitude of IB and K+ contractures.

The effects of NO on the normal beta-adrenergic cardiac function and myocardial contractility were analyzed in anesthetized dogs. Inhibition of NOS activity by NG-nitro-L-arginine methyl ester in anesthetized, autonomically blocked dogs augmented cardiac peripheral inotropic response to beta-adrenergic receptor activation. However, basal myocardial contractility was not altered by dobutamine- and isoproterenol-mediated cardiac NOS inhibition.