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Endogenous polyamines mediate acute metabolic effects and cardiac hypertrophy associated to beta-adrenoceptor stimulation. The aim of this study is to characterize the role of polyamines on beta-adrenoceptor system mediated responses. To this end, the functional interaction of polyamine modifying drugs on isoproterenol-elicited cardiotonic effect, in isolated left atria of male Wistar rats, and their effects on [(3)H]dihydroalprenolol (DHA) binding on beta-adrenoceptors and on adenylyl cyclase activity of membrane heart were studied. Polyamines interact with beta-adrenoceptors in rat heart, as shown by the displacement of [(3)H]DHA binding. Furthermore, putrescine (but not spermidine or spermine) increased adenylyl cyclase activity, elicited a positive inotropism and increased intracellular cAMP. The putrescine effect on adenylyl cyclase was not antagonized by the beta-adrenoceptors blockers, alprenolol and ICI-118,551, and facilitated the isoproterenol effect. Neither alprenolol, atenolol nor ICI-118,551 antagonized putrescine-elicited positive inotropism. However, the effect was abolished in preparations with desensitized beta-adrenoceptors. alpha-Difluoromethylornithine, an inhibitor of ornithine decarboxylase, antagonized the effect of isoproterenol on inotropism and cAMP increase. In addition, putrescine might elicit effects by mechanisms independent of beta-adrenoceptor system, since in left atria with functional desensitized receptors an interaction with ouabain-elicited cardiotonic effect was observed. These results suggest that putrescine may act as a low affinity agonist on beta-adrenoceptors and modulate acute responses mediated by beta-adrenoceptors. These findings may be of importance in the physiology and in diseases involving cardiac beta-adrenoceptors.

Molecular interactions of androgens with the plasma membrane may produce rapid cardiovascular effects that cannot be explained by the classic genomic mechanisms. In this sense, 5 alpha- and 5 beta-dihydrotestosterone-induced an acute positive inotropic effect in isolated left atrium of rat, an effect which may be due to cAMP-dependent mechanisms. To prove this, intracellular levels of cAMP, after exposure to androgens in the organ bath, and binding to beta(1)-adrenoceptors were evaluated. After a 4-min exposure, 5 alpha- and 5 beta-dihydrotestosterone increased cAMP levels from 3.83+/-0.61 to 6.15+/-1.1 and 11.18+/-2.4 pmol cAMP/mg of protein, respectively. These increases were inhibited by atenolol and not modified by treatment of the rats with reserpine. The androgen-induced cAMP increase seems to be produced via an extracellular interaction, because positive inotropism and raised levels of cAMP were produced by 5 alpha-dihydrotestosterone conjugated with bovine serum albumin (BSA). In addition, it is independent of beta(1)-adrenoceptor activation, because neither androgen displaced [(3)H]dihydroalprenolol binding. Therefore, the androgens induced a positive inotropic effect via a postsynaptic effect that increases intracellular levels of cAMP. This effect is modulated by transcriptional mechanisms or by a protein with a short half-life.

The genetically epilepsy-prone rat (GEPR) seizure model is characterized by extensive abnormalities in brain noradrenergic function. Earlier studies had suggested that GEPRs might not regulate adrenoceptors in a normal fashion. The purpose of the present study was to determine if GEPR-9s are capable of up and down regulation of alpha(1)- and beta-adrenoceptors in response to increments or decrements in extracellular norepinephrine. Seizure induction has been shown to increase extracellular norepinephrine. Chronic sound or electroshock-induced seizures caused down regulation of beta-adrenoceptors in frontal cortex and in hippocampus from GEPR-9s. Similarly, chronic daily treatment with the norepinephrine reuptake inhibitor desmethylimipramine produced down regulation of beta-adrenoceptors in frontal cortex and in hippocampus from GEPR-9s. As is the case in neurologically normal animals, chronic electroshock-induced seizure did not cause down regulation of beta-adrenoceptors in 6-hydroxydopamine pretreated GEPR-9s. Chronic electroshock treatment also caused up-regulation of alpha(1)-adrenoceptors in frontal cortex but not in hippocampus. In 6-hydroxydopamine pretreated GEPR-9s, chronic electroshock treatment caused a further up-regulation of alpha(1)-adrenoceptors in frontal cortex but not in hippocampus. Taken together, these results indicate that GEPR-9s are capable of up and down regulation of alpha(1)- and beta-adrenoceptors in a manner that is qualitatively similar to the regulation of these receptors in normal animals. Whether the regulation of brain adrenoceptors is quantitatively different in GEPRs from normal animals remains to be established.

The binding of [3H]dihydroalprenolol to beta-adrenergic receptors in the rat brainstem was studied. Propranolol inhibited dihydroalprenolol binding to a greater extent than did isoproterenol or epinephrine. Scatchard plots obtained with propranolol were biphasic whereas those obtained with isoproterenol and epinephrine were monophasic. The results indicate that in the brainstem propranolol displaces dihydroalprenolol from sites other than beta-adrenergic receptors. Nonspecific binding of dihydroalprenolol in this tissue therefore cannot be assayed using propranolol but should be measured with isoproterenol or epinephrine.

The cardiac beta-adrenergic response to noradrenaline (NA) was investigated in the rat neonatally s.c. treated with 6-hydroxydopa (6-OHDOPA, 75 mg/kg, 0, 2 and 4 days after birth). 6-OHDOPA treatment significantly (P < 0.05) reduced the NA content by 32% of the control in whole heart and markedly potentiated the isoproterenol (0.17 mg/kg, i.p.)-induced stimulation of ornithine decarboxylase activity which had been blocked by a preceding i.p. injection of propranol (10 mg/kg) at the adult stage. Scatchard analysis of the specific [3H]-dihydroalprenolol ([3H]DHA0 binding indicated that 6-OHDOPA induced an increase in the maximum number of specific binding sites of [3H]DHA but did not alter the dissociation constant. In addition, 6-OHDOPA treatment resulted in a potentiation of the positive inotropic response to NA but not to isoproterenol in isolated atria. It is suggested that 6-OHDOPA treatment produces an increased density of beta-adrenergic receptor sites relevant to the hypersensitivity of beta-receptors to NA.

An analysis of Hofstee plots of specific [3H]dihydroalprenolol ([3H]DHA) binding in the presence of various concentrations of practolol showed that KD and Bmax in beta 1-subtype adrenoceptors were 19.2-fold lower and 2.76-fold higher than those in beta 2-subtype in adult rat hearts, respectively. Neonatal treatment with 6-hydroxydopa produced a significant increase only in Bmax in beta 1-adrenoceptors without changing Bmax and KD in beta 2-receptors. "Up' regulation in the density of beta 2-type of adrenoceptors seems to be caused by the 6-hydroxydopa-induced sympathetic lesion.

Two types of saturable binding, besides the well-known non-specific binding, were found when hydrophobic ligands were used for investigating the vesiculization of beta-adrenoceptors on cultured HeLa and Chang liver cells. The first (compartment I) representing beta-adrenoceptors with high affinity ([3H]DHA 0.8 nM, 125I-CYP 27 pM) and low capacity (10-20 fmol/mg protein), the second (compartment II) had a rather high affinity ([3H]DHA 400 nM, 125I-CYP 30 nM) and a very high capacity (20 000-25 000 fmol/mg protein). The affinity of adrenergic agents for compartment II correlates very well (r = 0.9418) with the calculated hydrophobicity. It is concluded that these types of binding sites might interfere with the determination of adrenoceptor binding sites when hydrophobic ligands are used. When using hydrophobic ligands like these special care should be taken to avoid such interference.

The concentration of alpha- and beta-adrenergic receptors--as measured by specific [3H]WB-4101 and (-)-[3H]dihydroalprenolol binding--was diminished by 60% below control values in the hearts of rats exposed to tobacco smoke. These changes in receptor numbers took place almost immediately after tobacco smoke exposure and were rapidly reversible after termination of the exposure. The dissociation constant, KD, for [3H]WB-4101 was identical in exposed (KD = 0.34 +/- 0.09 nM) and control (KD = 0.35 +/- 0.07 nM) hearts but was significantly different in the case of (-)-[3H]dihydroalprenolol binding (exposed, KD = 2.83 +/- 0.30 mM vs. control KD = 5.22 +/- 0.61 nM). For beta-receptor binding there was no significant difference between exposed and control animals in the Ki values for (-)-epinephrine, (-)-norepinephrine, (-)-alprenolol, (+/-)-propranolol or timolol. (-)-Isoproterenol, however, was found to bind with lower affinity in exposed compared with control hearts. For alpha-receptor binding there was no significant difference between control and 'smoked' animals in the Ki values for (-)-epinephrine, (-0)-norepinephrine or phentolamine. The decrease in alpha- and beta-adrenergic receptor concentration may be related to the phenomenon of receptor desensitization resulting from a release of catecholamines in rats exposed to tobacco smoke.

The characteristics of beta-adrenoceptors on frog and chick erythrocytes have been compared to those present on rat erythrocyte, lung and cerebral cortical membranes. The receptors have been examined using the specific ligand [3H]dihydroalprenolol ([3H]DHA) with conventional filtration techniques. The equilibrium dissociation constant (KD) of [3H]DHA and the affinities of the non-selective beta-adrenoceptor antagonists propranolol, timolol and alprenolol, were very similar in all preparations examined. The relative order of potency of the catecholamines, isoprenaline greater than adrenaline greater than noradrenaline in rat lung, rat erythrocyte and frog erythrocyte; isoprenaline greater than noradrenaline greater than or equal to adrenaline in chick erythrocyte and rat cortex, suggest an overall beta 2-classification for the former and beta 1-classification of the latter tissues. However, the use of highly selective beta 1- or beta 2-agents and computer-assisted iterative curve fitting revealed that whereas rat cortex and lung possess both receptor subtypes (lung 80% beta 2, 20% beta 1: cortex 65% beta 1, 35% beta 2) only beta 2-sites were observed in rat erythrocytes. On the other hand, chick and frog erythrocytes possess a homogeneous population of receptors that do not strictly correspond either to beta 1- or beta 2-adrenoceptors. The atypical nature of these non-mammalian erythrocyte beta-adrenoceptors is discussed in relation to their previous extensive use as model beta-adrenoceptor systems.

The high affinity binding sites for 3H-imipramine (3H-IMI) and 3H-dihydroalprenolol (3H-DHA) in the rat cerebral cortex were studied after 2,4 48 and 72 h of rapid-eye-movement (REM) sleep deprivation. Both the Kd and Bmax values for 3H-IMI and 3H-DHA binding remained unaffected after 24 or 48 h of REM sleep deprivation. After 72 or REM sleep deprivation there was a significant reduction in the Bmax for 3H-IMI and 3H-DHA binding with a concomitant increase in the apparent affinities. The reduction in high affinity 3H-IMI and 3H-dihydroalprenolol binding sites observed 72 h after REM sleep deprivation could be related to the antidepressant effects of REM sleep deprivation in man.

The effects of yohimbine on desipramine-induced adrenoreceptor alterations were examined in murine limbic forebrain areas. Treatment with both drugs in combination resulted in a significant decrease in [3H]dihydroalprenolol binding, which was not manifest after treatment with either drug alone. Moreover, co-administration of yohimbine was found to accelerate the time course and increase the magnitude of desipramine-induced increases in [3H]clonidine binding. The possible physiologic significance of these findings is discussed along with their pharmacologic implications.

Subacute administration (b.i.d. for 4 days) of sertraline, a potent and selective inhibitor of serotonin uptake, was found to reduce cyclic AMP generation by the norepinephrine receptor-coupled adenylate cyclase in rat limbic forebrain slices and decrease the number of beta-adrenoceptors in rat cerebral cortex without affecting the affinity of [3H]dihydroalprenolol binding. Co-administration of sertraline and the serotonin agonist, quipazine, at doses at which neither agent had an effect, resulted in desensitization of norepinephrine receptor-coupled adenylate cyclase and down-regulation of beta-adrenoceptors. These findings suggest that increased serotonergic activity may be involved in the induction of subsensitivity of the beta-adrenoceptor system of rat brain by sertraline.

We examined effects of treatment with cardiac glycosides, in combination with noradrenergic stimulation or depletion, on (Na+,K+)-ATPase activity in rat cerebral cortex, heart, and kidney. Treatment with digitoxin increased the apparent number of (Na+,K+)-ATPase sites in heart, cerebral cortex, and kidney. Ouabain, which crosses the blood-brain barrier poorly, did not affect enzyme in brain but was otherwise similar. Norepinephrine depletion prevented the increase in heart but not in cerebral cortex. Noradrenergic stimulation increased the number of sites in cerebral cortex and in heart. In rats treated with digitoxin, noradrenergic stimulation increased enzyme activity further in heart but not in cerebral cortex. Examination of effects on noradrenergic receptor binding and on norepinephrine metabolite concentrations suggested that, while in heart cardiac glycosides appeared to increase norepinephrine release, in brain there was no effect on release but there may have been appreciable inhibition of norepinephrine reuptake under stimulated conditions.

Chronic treatment with propranolol for 6 weeks resulted in a 16.6% increase, over the level in control rats, in myocardial alpha 1-adrenoceptor density as measured by [3H]prazosin binding. The apparent affinity remained unaffected. No changes were observed in beta-adrenoceptor density and apparent affinity as measured by [3H]dihydroalprenolol binding. It is concluded that myocardial alpha 1-adrenoceptors might have a compensatory role under conditions where beta-adrenergic effects are attenuated.

A photoaffinity probe for alpha 1-adrenoceptors was synthesized and its properties examined on rat brain membrane preparations. The binding of 4-amino-2-[4-(4-azidocinnamoyl)piperazino]-6,7-dimethoxyquin azoline (ACP) to these receptors was of high affinity (KD = 1.05 nM) and reversible in the dark. A dose-dependent decrease in the concentration of [3H]prazosin binding sites without a change in KD was observed when membranes were preincubated with ACP, photolyzed, and then extensively washed prior to assay. This reduction in receptor concentration was prevented by alpha 1-adrenergic ligands. The specificity of ACP for alpha 1-receptors was further demonstrated by its inability to compete with [3H]dihydroalprenolol and [3H]yohimbine binding in these same membranes. Also, the concentrations and affinity constants of beta-adrenoceptors and alpha 2-adrenoceptors were unaffected in membranes which had been photolyzed after preincubation with ACP. No reduction in concentration of alpha 1-adrenoceptors was detected if ACP was photolyzed prior to incubation with receptors or if ACP was maintained in darkness throughout the experiment. The results suggest that ACP is a specific and sensitive photoprobe that may be useful for further studies on alpha 1-adrenoceptor coupled systems and that may be particularly suited for use in cell culture work.

In rats receiving repeated injections of imipramine, there is a reduction in the number of high affinity binding sites for [3H]imipramine and [3H]dihydroalprenolol present in crude synaptic membrane preparations from various brain structures. The location of the sites that become subsensitive to the two ligands did not coincide; the binding sites to [3H]imipramine became subsensitive in the hippocampus but not in cortex or cerebellum. In contrast the binding sites to [3H]dihydroalprenolol became subsensitive in cortex and cerebellum but not in hippocampus. It can be suggested that in rats repeatedly treated with imipramine the down regulation of beta-adrenergic receptors may not coincide with the down regulation of the high affinity binding sites for imipramine. Such a dissociation is supported further by experiments with rats treated with iprinidol.

The influence of thyroid hormone deficiency on beta-adrenoceptors in the rat cerebral cortex was investigated using the 3H-dihydroalprenolol binding assay. The maximal number of binding sites (Bmax) and the dissociation constants (KD) were determined in the brain tissue from euthyroid animals and from rats made hypothyroid by feeding 6-propyl-2-thiouracil. Hypothyroidism resulted in a 37% decrease in beta-adrenoceptor density (Bmax). The dissociation constants (KD) of both groups were not significantly different.

Treatment of rats with triiodothyronine (T3 10 micrograms/100 g per day, 20 days) increased the mass of brown adipose tissue (BAT) and heart ventricle and stimulated beta-adrenoreceptor number (assessed from radioligand binding) by 43% in isolated BAT and heart membranes. alpha-Receptor number was slightly increased in BAT membranes (42%) but reduced in heart from T3-treated rats. The ratio of alpha-receptors/beta-receptors was unaffected by T3 treatment in BAT membranes (control and hyperthyroid = 1.54) but reduced in heart (control = 2.8, T3 = 1.04).

Administration of the combination of antidepressant and neuroleptic drugs has been reported to have a synergistic effect in the treatment of delusional depression. The effects of chronic coadministration of imipramine (IMIP) and chlorpromazine (CPZ) on beta-adrenergic and alpha 2-adrenergic binding sites in rat cerebral cortex were studied. The combination caused the same reduction in the number of beta-adrenergic receptors as IMIP alone. No changes in alpha 2-adrenergic receptors were observed with IMIP and/or CPZ.

In vitro incubation of rat cerebral cortex slices with antidepressant drugs reduced beta-adrenergic receptor binding of 3H-dihydroalprenolol by 30%. The decrease was maximum after 60 min, and was reversible after 120 min. (-)-Isoproterenol incubation caused a rapid and reversible loss (60%) of beta-receptor binding. Both effects were due to a decrease in beta-receptor sites. In vitro beta-receptor subsensitivity due to desipramine and isoproterenol was non-additive. The observed reversible loss of beta-receptor sites may be an initial phase of the beta-receptor down-regulation by antidepressants seen in vivo.

The alpha 1- and beta-adrenergic and muscarinic cholinergic receptors in guinea-pig nasal mucosa were measured for the first time by direct binding techniques using [3H]prazosin, [3H]dihydroalprenolol ([3H]DHA) and [3H]quinuclidinyl benzilate ([3H]QNB). The maximum binding capacities of [3H]prazosin, [3H]DHA and [3H]QNB in guinea-pig nasal mucosa were 20.1, 42.3, 159 fmol/mg protein, respectively. The dissociation constants of [3H]prazosin, [3H]DHA and [3H]QNB in guinea-pig nasal mucosa were 0.37, 0.77 and 1.5 nM, respectively. After the removal of the superior cervical ganglion in the guinea-pig, the number of alpha 1-adrenergic receptors was increased in the nasal mucosa while the number of beta-adrenergic and muscarinic receptors remained unchanged. Thus, alpha 1-adrenergic receptors are probably postsynaptic receptors in the target cells of sympathetic nerves, while beta receptors relate to the circulating catecholamines.

The ability of the beta 1 partial agonists prenalterol and corwin , to displace the binding of [3H]dihydroalprenolol to the heterogeneous populations of beta-adrenoceptors on rat and rabbit lung membranes was compared. Both drugs exhibited higher affinity for the binding sites in rabbit lung (predominant beta 1) as compared to rat lung (predominant beta 2). Curve fitting analysis of the displacement curves into high affinity (beta 1) and low affinity (beta 2) components indicates that both drugs exhibit beta 1 selective affinity. Further competition experiments performed in the presence of carefully calculated concentrations of highly selective beta 1 (atenolol) or beta 2 (ICI 118,551) antagonists to produce homogeneous receptor subtype populations in rat and rabbit lung membranes respectively, confirmed this beta 1 selective affinity. These results suggest an approximate selective affinity ratio (beta 1 to beta 2) of ten and forty fold for prenalterol and corwin respectively.

The binding of three adrenergic ligands ([3H]prazosin, [3H]clonidine, [3H]dihydroalprenolol) was studied in the frontal cortex of human brain. alpha 1-Receptors, labeled by [3H]prazosin, predominated. [3H]Clonidine bound to two classes of sites, one of high affinity and one of low affinity. Guanosine triphosphate appeared to lower the affinity of [3H]clonidine for its receptor. [3H]Dihydroalprenolol bound to three classes of sites: the beta 1-receptor, the beta 2-receptor and a receptor with low affinity which represented about 40% of the total binding, but which was probably a non-specific site; the beta 1/beta 2 ratio was 1/2.

The beta-adrenergic antagonist, [3H]dihydroalprenolol, was used to label binding sites in crude rat myocardial plasma membranes. The specificity of binding was dependent on the temperature of the assay. Specific binding at 22 and 37 degree C and at concentrations of radioligand less than 5 nM was consistent with binding to the myocardial beta-receptor. Binding sites labeled at 4 degree C possessed quite different properties. Binding was non-stereoselective and of lower affinity. Agonist compounds were much less effective at competing for the labeled myocardial sites at 4 degree C than at 22 degree C. Those beta-antagonists which additionally possess pharmacological "quinidine-like' activity (e.g. propranolol, alprenolol) were potent competitors at 4 degree C, but competition was non-stereoselective. In contrast atenolol, a beta-antagonist devoid of "quinidine-like' activity was ineffective at 4 degree C. Furthermore, procaine, and quinidine itself were potent competitors of [3H]dihydroalprenolol binding at 4 degree C. Thus the specificity of [3H]dihydroalprenolol binding to rat heart membranes at 4 degree C appears to be directed non-stereoselectively at that portion of the competing molecule which recognized "quinidine-like' as opposed to adrenergic activity.

Specific beta-adrenergic receptors were characterized in rat ovary, using an in vitro receptor binding assay with [3H]dihydroalprenolol. The ligand was bound to a single class of saturable and high affinity receptors (dissociation constant = 3.5 nM and maximum capacity = 3.4 pmol/g tissue). In competition studies, the binding was stereoselective for the (-)-isomer of isoproterenol. Known beta-adrenergic agonists displaced the ligand from ovarian receptors with the following order of potency: isoproterenol greater than epinephrine much greater than norepinephrine, which is typical for a beta 2-adrenergic receptor.

Sodium ascorbate addition caused a modest loss in the specific binding of [3H]dihydroalprenolol ([3H]DHA) in a rat cortical membrane preparation. Sodium ascorbate also caused a modest increase in lipid peroxide formation in the membrane preparation. Both the lipid peroxidation and the loss in [3H]DHA binding were greatly potentiated by the addition of low levels of iron (Fe2+). A kinetic analysis indicated that the iron/ascorbate caused a loss in the number of [3H]DHA binding sites but had no effect on the affinity of [3H]DHA for the binding site. Both the lipid peroxidation and the loss of [3H]DHA binding were prevented by iron chelating agents (e.g. EDTA) and by classical inhibitors of lipid peroxidation (e.g. propyl gallate, cobalt chloride). All of these data taken together suggest that an iron-dependent lipid peroxidation results in a loss of [3H]DHA binding sites. These and other data further suggest that lipid is critical for the binding of [3H]DHA to its receptor.

In this study we compared characteristics of (-)-[3H]dihydroalprenolol ([3H]DHA) binding sites in crude membrane preparations of human peripheral blood lymphocytes with those of intact, viable cells. A valid determination of specific beta-adrenergic receptor binding in both preparations was obtained by defining non-specific [3H]DHA binding with 10(-6) M l- or dl-propranolol or 10(-3) M l-isoproterenol. Higher concentrations of propranolol were used in prior reports on lymphocyte membranes. We showed that these concentrations may inhibit non-specific binding, causing non-saturability and inhomogeneity of the estimated 'specific' binding. In the intact cell preparations, inclusion of 10(-4) M phentolamine was necessary to reduce the high degree of non-specific binding. By contrast, phentolamine (10(-4) M) showed no effect on the [3H]DHA binding to membrane preparations. At 37 degrees C the [3H]DHA binding to beta-adrenergic receptor sites in both intact and broken cell preparations was rapid and reversible. The sites were stereoselective, as l-propranolol was about two orders of magnitude more potent to inhibit [3H]DHA binding than was the d-isomer. In both preparations, agonists competed for specific binding with a rank order of potency isoproterenol greater than epinephrine greater than norepinephrine, which indicated a beta 2-type of adrenergic receptor. The specific [3H]DHA binding was saturable and Scatchard analysis revealed comparable numbers of homogeneous, non-cooperative binding sites (approximately 1250 receptors/cell in the membrane preparations and 1700 receptors/cell in the intact cells). In spite of these similarities the membrane sites showed a lower affinity for the antagonists [3H]DHA and propranolol than did the intact cell sites, whereas their affinity for the agonists was increased. These differences indicate that the membrane system might be less suited to provide physiologically significant information about the beta-adrenergic receptor system.

In rats receiving (-)-deprenyl (1 mumol/kg, s.c.) twice daily for 3 weeks, the Bmax of imipramine binding sites located in crude synaptic membranes prepared from frontal cortex increases while the NE stimulation of cAMP accumulation in minces prepared from frontal cortex is attenuated. The presence of intact 5HT axon terminals is an absolute requirement for the down-regulation of the beta-adrenergic receptor function by repeated injections of (-)-deprenyl. These and other lines of evidence suggest that the increase in the Bmax of [3H]imipramine binding sites and the attenuation of beta-adrenergic receptor function elicited by (-)-deprenyl might be causally related.

The disposition and activity of some beta-adrenoceptor antagonists in the rats was determined using an ex vivo receptor binding assay. Rats were injected with different doses of beta-adrenoceptor antagonists and the extent of receptor occupation was assessed in various tissues under in vitro conditions. Rats treated with (-)-propranolol (0.1 mumol. kg-1) displayed peak plasma levels of biologically active drug assayed by radioreceptor assay 15 min after administration. On the other hand, the highest concentration of bioactive drug, assessed by ex vivo assays, was observed at 30 min in all tissues examined. Dose-response curves revealed that (-)-propranolol was about 100 fold more potent than (+)-propranolol in all tissues examined, and that there was a small (3 fold) degree of selectivity for both isomers towards lung and spleen over heart, cortex and cerebellum. The affinity of (-)-propranolol in heart and lung using the ex vivo binding assay was similar to the affinity of this agent to inhibit in vivo isoprenaline-stimulated cyclic AMP formation in these tissues. The beta 1-selective antagonist (+/-)-atenolol demonstrated selectivity towards those tissues that have been previously shown to possess a predominance of beta 1-adrenoceptors, though penetration to the central nervous system was substantially less than propranolol. The inherent advantages of this ex vivo assay are discussed.

Bilateral 6-hydroxydopamine (6-OHDA) lesions of the dorsal noradrenergic bundle have been shown to increase [3H]dihydroalprenolol (DHA) binding in the rat hippocampus. The effect of adrenalectomy on this increase in receptor binding was examined. Groups of rats received stereotaxically placed 6-OHDA injections aimed at the dorsal bundle (DB) or vehicle injections (control). Half of each group subsequently received bilateral adrenalectomies (ADX) and the other half received sham operations, yielding four groups: control, DB, ADX, and DB + ADX. The DB lesions produced a 41% increase in maximum binding in close agreement with a previous report. No statistically significant change in [3H]DHA receptor binding was observed following adrenalectomy treatment alone. By contrast, the DB + ADX group showed a significant increase in maximum [3H]DHA receptor binding compared to the DB group. This adrenalectomy-induced increase was reversed after 1 week of corticosterone treatment (1.0 mg/kg/12 h, s.c.). These results suggest an interaction between noradrenergic mechanisms and corticosterone in the hippocampus.

Exploratory behaviour was measured in the open-field at 8.00 h and 20.00 h with naive rats and rats treated with an alpha 1-agonist (phenylephrine, 25 micrograms i.c.v.) or beta-agonists (salbutamol, 2.5 mg/kg; clenbuterol 0.05 mg/kg i.p.). The spontaneous activity was similar at both times, yet the response to a alpha 1-as well as to beta-stimulation was significantly enhanced at 20.00 h. The density of cortical [3H]prazosin and [3H]dihydroalprenolol ([3H]DHA) binding sites at 20.00 h was enhanced by 19% and 28% respectively, in comparison with the density measured at 8.00 h.