Search

Am J Physiol Regul Integr Comp Physiol 298: R51-R60, 2010. First published November 4, 2009; doi: 10.1152/ajpregu.00576.2009.--Hypoxic pulmonary vasoconstriction (HVC), an intrinsic and assumed ubiquitous response of mammalian pulmonary blood vessels, matches regional ventilation to perfusion via an unknown O2-sensing mechanism. Global pulmonary hypoxia experienced by individuals suffering from chronic obstructive pulmonary disease or numerous hypoventilation syndromes, including sleep apnea, often produces maladaptive pulmonary hypertension, but pulmonary hypertension is not observed in diving mammals, where profound hypoxia is routine. Here we examined the response of cow and sea lion pulmonary arteries (PA) to hypoxia and observed the expected HVC in the former and a unique hypoxic vasodilation in resistance vessels in the latter. We then used this disparate response to examine the [O.sub.2]-sensing mechanism. In both animals, exogenous [H.sub.2]S mimicked the vasoactive effects of hypoxia in isolated PA. [H.sub.2]S-synthesizing enzymes, cystathionine [beta]-synthase, cystathionine [gamma]-lyase, and 3-mercaptopyruvate sulfur transferase, were identified in lung tissue from both animals by one-dimensional Western blot analysis and immunohistochemistry. The relationship between [H.sub.2]S production/consumption and [O.sub.2] was examined in real time by use of amperometric [H.sub.2]S and [O.sub.2] sensors. H2S was produced by sea lion and cow lung homogenate in the absence of [O.sub.2], but it was rapidly consumed when [O.sub.2] was present. Furthermore, consumption of exogenous [H.sub.2]S by cow lung homogenate, PA smooth muscle cells, and heart mitochondria was [O.sub.2] dependent and exhibited maximal sensitivity at physiologically relevant [Po.sub.2] levels. These studies show that HVC is not an intrinsic property of PA and provide further evidence for [O.sub.2]-dependent [H.sub.2]S metabolism in [O.sub.2] sensing. hypoxic vasoconstriction; pinniped; pulmonary hypertension

Natriuretic peptides (NPs) are evolutionarily conserved hormones that affect blood pressure and fluid volume through membrane-bound guanylate cyclase (GC)-linked natriuretic peptide receptors-A and -B (NPR-A and NPR-B, respectively) in a variety of vascular, renal, and other tissues. The principal physiological stimulus for cardiac NPs in fish is somewhat debated between two prominent theories: regulation of salt balance (osmoregulatory hypothesis) or prevention of volume expansion (cardioprotective hypothesis). In the present study, we examined atrial and ventricular expression of trout NPs, atrial (ANP), brain (BNP), and ventricular (VNP) using Northern (mRNA), Western (NP pro-hormone), and qPCR (GC-NPR-A and -B mRNA) blot analysis following independent manipulation of plasma salt and volume levels after chronic exposure to freshwater (FW; volume loaded, salt depleted), saltwater (SW; volume depleted, salt loaded), or freshwater trout fed a high-salt diet (FW-HSD; volume and salt loaded). We also measured NP transcriptional response to acute (2 h) volume expansion with dialyzed plasma (VE; 80% blood vol) or volume depletion by hemorrhage (VD, 20% blood volume every 30 min for 2 h) with real-time PCR. In essentially all instances, increased expression of the NP system was associated with FW-HSD or plasma expansion. There were no differences in NP expression between chronically adapted FW and SW fish, and hemorrhage decreased atrial ANP and VNP mRNA. These results indicate that rainbow trout cardiac NPs and cardiovascular GC-NPRs respond principally to volume, not salt overload, and this suggests that the primary function of trout cardiac NP system is to protect the heart. natriuretic peptide receptors; hypervolemia; hypervolemia; osmoregulation; cardioprotection

Carbon monoxide (CO) is endogenously produced by heme oxygenase (HO) and is involved in vascular, neural, and inflammatory responses in mammals. However, the biological activities of CO in nonmammalian vertebrates is unknown. To this extent, we used smooth muscle myography to investigate the effects of exogenously applied CO (delivered via a water-soluble CO-releasing molecule, CORM-3) on isolated lamprey (Petromyzon marinus) dorsal aortas and examined its mechanisms of action on trout (Oncorhynchus mykiss) efferent branchial (EBA) and celiacomesenteric (CMA) arteries. CORM-3 dose-dependently relaxed all vessels examined. Trout EBA were twofold more sensitive to CORM-3 when precontracted with norepinephrine (NE) than KC1 and CORM-3 relaxed five-fold more of the NE--than KC1-induced tension. Glybenclamide (10 [micro]M), an ATP-sensitive potassium channel inhibitor, inhibited NE-induced contraction, but did not affect CORM-3-induced relaxation. NS-2028 (10 [micro]M), a soluble guanylyl cyclase inhibitor, had no effect on a NE-contraction, but inhibited a subsequent CORM-3-induced relaxation. Zinc protopophyrin-IX (ZnPP-IX, 0.3-30 [micro]M), a HO inhibitor, elicited a small, yet dose-dependent and significant, increase in baseline tension but did not have any effect on subsequent NE-induced contractions or a nitric oxide-induced relaxation (via sodium nitroprusside). [ZnPP-IX] greater than 3 [micro]M, however, significantly reduced the predominant vasodilatory response of trout EBA to hydrogen sulfide. These results implicate an active HO/CO pathway in trout vessels having an impact on resting vessel tone and CO-induced vasoactivity that is at least partially mediated by soluble guanylyl cyclase. gasotransmitters; guanylyl cyclase; hydrogen sulfide; vasodilator

[O.sub.2] chemoreceptors elicit cardiorespiratory reflexes in all vertebrates, but consensus on [O.sub.2]-sensing signal transduction mechanism(s) is lacking. We recently proposed that hydrogen sulfide ([H.sub.2]S) metabolism is involved in [O.sub.2] sensing in vascular smooth muscle. Here, we examined the possibility that [H.sub.2]S is an [O.sub.2] sensor in trout chemoreceptors where the first pair of gills is a primary site of aquatic [O.sub.2] sensing and the homolog of the mammalian carotid body. Intrabuccal injection of [H.sub.2]S in unanesthetized trout produced a dose-dependent bradycardia and increased ventilatory frequency and amplitude similar to the hypoxic response. Removal of the first, but not second, pair of gills significantly inhibited [H.sub.2]S-mediated bradycardia, consistent with the loss of aquatic chemoreceptors, mRNA for [H.sub.2]S-synthesizing enzymes, cystathionine [beta]-synthase and cystathionine [gamma]-lyase, was present in branchial tissue. Homogenized gills produced [H.sub.2]S enzymatically, and [H.sub.2]S production was inhibited by [O.sub.2], whereas mitochondrial [H.sub.2]S consumption was [O.sub.2] dependent. Ambient hypoxia did not affect plasma [H.sub.2]S in unanesthetized trout, but produced a [Po.sub.2]-dependent increase in a sulfide moiety suggestive of increased [H.sub.2]S production. In isolated zebrafish neuroepithelial cells, the putative chemoreceptive cells of fish, both hypoxia and [H.sub.2]S, produced a similar ~10-mV depolarization. These studies are consistent with [H.sub.2]S involvement in [O.sub.2] sensing/signal transduction pathway(s) in chemoreceptive cells, as previously demonstrated in vascular smooth muscle. This novel mechanism, whereby [H.sub.2]S concentration ([[H.sub.2]S]) is governed by the balance between constitutive production and oxidation, tightly couples tissue [[H.sub.2]S] to [Po.sub.2] and may provide an exquisitely sensitive, yet simple, [O.sub.2] sensor in a variety of tissues. hydrogen sulfide concentration

Hydrogen sulfide ([H.sub.2]S) is rapidly emerging as a biologically significant signaling molecule. Studies published before 2000 report low or undetectable [H.sub.2]S (usually as total sulfide) levels in blood or plasma, whereas recent work has reported sulfide concentrations between 10 and 300 [micro]M, suggesting it acts as a circulating signal. In the first series of experiments, we used a recently developed polarographic sensor to measure the baseline level of endogenous [H.sub.2]S gas and turnover of exogenous [H.sub.2]S gas in real time in blood from numerous animals, including lamprey, trout, mouse, rat, pig, and cow. We found that, contrary to recent reports, [H.sub.2]S gas was essentially undetectable (< 100 nM total sulfide) in all animals. Furthermore, exogenous sulfide was rapidly removed from blood, plasma, or 5% bovine serum albumin in vitro and from intact trout in vivo. To determine if blood [H.sub.2]S could transiently increase, we measured oxygen-dependent [H.sub.2]S production by trout hearts in vitro and in vivo. [H.sub.2]S has been shown to mediate ischemic preconditioning (IPC) in mammals. [PC is present in trout and, unlike mammals, the trout myocardium obtains its oxygen from relatively hypoxic systemic venous blood. In vitro, myocardial [H.sub.2]S production was inversely related to P[O.sub.2], whereas we failed to detect [H.sub.2]S in ventral aortic blood from either normoxic or hypoxic fish in vivo. These results provide an autocrine or paracrine mechanism for myocardial coupling of hypoxia to [H.sub.2]S in [PC, i.e., oxygen sensing, but they fail to provide any evidence that [H.sub.2]S signaling is mediated by the circulation. gasotransmitter; hydrogen sulfide metabolism; vascular signaling

Trout are of interest in defining the relationship between fluid and salt balance on cardiovascular function because they thrive in freshwater (FW; volume loading, salt depleting), saltwater (SW; volume depleting, salt loading), and FW while fed a high-salt diet (FW-HS; volume and salt loading). The effects of chronic (>2 wk) adaptation to these three protocols on blood volume ([sup.51]Cr red cell space), extracellular fluid volume ([sup.99m]Tc-diethylene triaminepenta-acetic acid space), arterial (dorsal aortic; PDA) and venous (ductus Cuvier; [P.sub.ven) blood pressure, mean circulatory filling pressure (zero-flow [P.sub.ven]), and vascular capacitance were examined in the present study on unanesthetized rainbow trout. Blood volume, extracellular fluid volume, [P.sub.DA], [P.sub.ven], and mean circulatory filling pressure progressively increased in the order SW < FW < FW-HS. Vascular capacitance in SW fish appeared to be continuous with the capacitance curve of FW fish and reflect a passive volume-dependent unloading of the venous system of FW fish. Vascular capacitance curves for FW-HS fish were displaced upward and parallel to those of FW fish, indicative of an active increase in unstressed blood volume without any change in vascular compliance. These studies are the first in any vertebrate to measure the relationship between fluid compartments and cardiovascular function during independent manipulation of volume and salt balance, and they show that volume, but not salt, balance is the primary determinant of blood pressure in trout. They also present a new paradigm with which to investigate the relative contributions of water and salt balance in cardiovascular homeostasis. fish; unstressed blood volume; mean circulatory filling pressure; osmoregulation; ionoregulation

Experiments were conducted on rainbow trout to determine the impact of dietary salt on arterial blood pressure. After 4-6 wk, fish fed a salt-enriched diet exhibited a 37% elevation of dorsal aortic pressure (from 23.8 [+ or -]1.2 to 32.6 [+ or -] 1.4 mmHg) and an 18% increase in ventral aortic pressure (from 33.0 [+ or -] 1.5 to 38.9 [+ or -] 1.3 mmHg). The hypertension presumably reflected the increase in cardiac output (from 31.0 [+ or -] 0.8 to 36.4 [+ or -] 2.2 ml.[min.sup.-1]. [kg.sup.-1]) because systemic and branchial resistances were statistically unaltered by salt feeding. The chronic hypertension was associated with a decrease in the pressor responses of the systemic vasculature to catecholamines and hypercapnia in the salt-fed fish. The reduction in [alpha]-adrenergic responsiveness of the systemic vasculature is consistent with desensitization or loss of functional [alpha]-adrenoceptors ([alpha]-ARs). In support of this idea, the salt-fed fish exhibited significantly decreased levels of [[alpha].sub.1D]-AR mRNA in the dorsal aorta and the afferent (ABA) and efferent branchial arteries (EBA). In contrast, however, the results obtained from norepinephrine doseresponse curves for EBA and ABA vascular rings in vitro did not provide evidence for loss of function of branchial artery [[alpha].sub.1]-ARs in the salt-fed fish. Indeed, the [EC.sub.50] for the EBA norepinephrine doseresponse curve was significantly reduced (from 3.75 x [10.sup.-7] to 2.12 x [10.sup.-7] M) in the salt-fed fish, indicating an increase in the binding affinity of the [[alpha].sub.1]-ARs. norepinephrine; epinephrine; blood pressure; systemic resistance; salt feeding; hypercapnia; efferent branchial artery; afferent branchial artery

Hydrogen sulfide ([H.sub.2]S) is a recently identified endogenous vasodilator in mammals. In steelhead/ rainbow trout (Oncorhynchus mykiss, Osteichthyes), [H.sub.2]S produces both dose-dependent dilation and a unique dose-dependent constriction. In this study, we examined [H.sub.2]S vasoactivity in all vertebrate classes to determine whether [H.sub.2]S is universally vasoactive and to identify phylogenetic and/or environmental trends. [H.sub.2]S was generated from NaHS and examined in unstimulated and precontracted systemic and, when applicable, pulmonary arteries (PA) from Pacific hagfish (Eptatretus stouti, Agnatha), sea lamprey (Petromyzon marinus, Agnatha), sandbar shark (Carcharhinus milberti, Chondrichthyes), marine toad (Bufo marinus, Amphibia), American alligator (Alligator mississippiensis, Reptilia), Pekin duck (Anas platyrhynchos domesticus, Ayes), and white rat (Rattus rattas, Mammalia). In otherwise unstimulated vessels, NaHS produced 1) a dose-dependent relaxation in Pacific hagfish dorsal aorta; 2) a dose-dependent contraction in sea lamprey dorsal aorta, marine toad aorta, alligator aorta and PA, duck aorta, and rat thoracic aorta; 3) a threshold relaxation in shark ventral aorta, dorsal aorta, and afferent branchial artery and 4) a multiphasic contraction-relaxation-contraction in the marine toad PA, duck PA, and rat PA. Precontraction of these vessels with another agonist did not affect the general pattern of NaHS vasoactivity with the exception of the rat aorta, where relaxation was now dominant. These results show that [H.sub.2]S is a phylogenetically ancient and versatile vasoregulatory molecule that appears to have been opportunistically engaged to suit both organspecific and species-specific homeostatic requirements. cardiovascular; fish; amphibian; reptile: bird; mammal: evolution

Dombkowski, Ryan A., Michael J. Russell, and Kenneth R. Olson. Hydrogen sulfide as an endogenous regulator of vascular smooth muscle tone in trout. Am J Physiol Regul Integr Comp Physiol 286: R678-R685, 2004; 10.1152/ajpregu.00419.2003.--Hydrogen sulfide ([H.sub.2]S) is an endogenous vasodilator in mammals, but its presence and function in other vertebrates is unknown. We generated [H.sub.2]S from NaHS and examined the effects on isolated efferent branchial arteries from steelhead (stEBA) or rainbow (rtEBA) trout. [H.sub.2]S concentration was measured colorimetrically (CM) and with ion-selective electrodes (ISE) in rainbow trout plasma. NaHS produced a triphasic response consisting of a relaxation (phase 1), constriction (phase 2), and relaxation (phase 3) in both unstimulated vessels and in stEBA precontracted with carbachol (Carb). Phase 1 and phase 3 in stEBA were decreased and phase 2 increased in unstimulated vessels by [[K.sup.+].sub.ATP] channel inhibition (glibenclamide), or a cocktail of inhibitors of cyclooxygenase, lipoxygenase, and cytochrome P-450 (indomethacin, esculetin, and clotrimazole). Inhibition of soluble guanylate cyclase with ODQ or NS-2028 inhibited phase 3 in stEBA, although NaHS decreased cGMP production by rtEBA. stEBA phase 2 contractions were partially inhibited by the myosin light chain kinase inhibitor, ML-9, but unaffected by L-type calcium channel inhibition (methoxyverapamil), whereas contraction in rtEBA was partially inhibited by nifedipine or removal of extracellular calcium. Phase 3 relaxations were more pronounced in stEBA precontracted with Carb and norepinephrine (NE) than those contracted by KCl or [K.sub.2]S[O.sub.4]. stEBA phase 2 and phase 3 responses were dose dependent(E[C.sub.50] = 1.1 [+ or -] 1.2 x [10.sup.-3] M and 6.7 [+ or -] 0.9 x [10.sup.-5] M, respectively; n = 7). NaHS was also vasoactive in steelhead bulbus arteriosus, celiacomesenteric arteries, and anterior cardinal veins. Rainbow trout plasma sulfide concentration was 4.0 [+ or -] 0.3 x [10.sup.-5] M, n = 4 (CM) and 3.8 [+ or -] 0.4 x [10.sup.-5] M, n = 9 (ISE); similar to phase 3 E[C.sub.50]. Because NaHS has substantial vasoactive effects at physiological plasma concentrations, we propose that its soluble derivative, [H.sub.2]S, is a tonically active endogenous vasoregulator in trout. fish; cardiovascular; guanosine 3',5'-cyclic monophosphate; vasodilator; vasoconstrictor

Measurement of venous function in vivo is inherently difficult. In this study, we used the Hilbert transform to examine the dynamic relationships between venous pressure and cardiac output (CO) in rainbow trout whose blood volume was continuously increased and decreased by ramp infusion and withdrawal (I/W). The dorsal aorta and ductus Cuvier were cannulated percutaneously and connected to pressure transducers; a flow probe was placed around the ventral aorta. Whole blood from a donor was then I/W via the dorsal aortic cannula at a rate of 10% of the estimated blood volume per minute, and the duration of I/W was varied from 40, 60, 80, 90, 120, 230, 240, 260, 300, and 340 s. Compliance [change in ([Delta]) blood vol/Avenous pressure] was 2.8 [+ or -] 0.2 ml * mm[Hg.sup.-1] * [g.sup.1] (N = 25 measurements; 6 fish with closed pericardium) and 2.8 [+ or -] 0.3 ml* mm[Hg.sup.-1] * [kg.sup.1] (N = 19 measurements, 4 fish with open pericardium). Compliance was positively correlated with the duration of I/W, indicative of cardiovascular reflex responses at longer I/W durations. In trout with closed pericardium, CO followed venous pressure oscillations with an average time lag of 4.2 [+ or -] 1.0 s (N = 9); heart rate (HR) was inversely correlated with CO. These studies show that CO is entrained by modulation of venous pressure, not by HR. Thus, although trout have a rigid pericardium, venous pressure (vis-a-tergo), not cardiac suction (vis-a-fronte), appears to be the primary determinant of CO. Estimation of venous compliance by ramp-modulation of venous pressure is faster and less traumatic than classical capacitance measurements and appears applicable to a variety of vertebrate species, as does the Hilbert transform, which permits analysis of signals with disparate frequencies. fish cardiovascular system; blood transit time; cardiovascular time series; vascular compliance; Hilbert transform

Two protocols were used in the investigation of the sympathetic nervous system regulation of venous function in the rainbow trout. Various cardiovascular parameters were monitored in the course of the experiments which also included agonists and receptor blocking studies. Results reveal that the venous system in rainbow trout is responsive to epinephrine. It responds by mobilizing blood from unstressed to stressed compartments and by decreasing compliance.

The effects of natriuretic peptides and nitroprusside on trout venous function were examined. The trout were instrumented with pressure cannulas in the ventral aorta, dorsal aorta and ductus Cuvier while simultaneously monitoring the cardiac output during natriuretic peptide (NP) infusion. Results showed that NP decreased venous compliance, which in turn, resulted to a decrease in venous return.

The cardiac function of conscious Oncorhynchus mykiss trout was analyzed after the adminsitration of [Arg0,Trp5,Leu8]bradykinin (tBK) to determine the cardiovascular effects of the homologous BK. A triphasic pressor-depressor-pressor response was induced by tBK injections in conscious trout. The cardiovascular effects of tBK on Oncrohynchus mykiss was also mediated by several vasoactive systems that acted in multiple cardiovascular effectors.

Urotensin II is a 12-amino acid residue peptide localized in the tissues of the central nervous system in teleost fish. It shares high homology with somatostatin-14, and has been suggested to play an important role in the maintenance of cardiovascular function. Herein, it is shown that injections of a synthetic replicate the peptide causes an increase in blood pressure, heart rate, and cardiac output accompanied by bradycardia. It also caused vasoconstriction of efferent branchial arteries.

A study on tachykinins, a family of polypeptides, taken from the stomach of bowfin Amia calva shows that they have new structural features. Vascular resistance, arterial blood pressure and cardiac output are affected by these peptides. One peptide has substance P-like immunoreactivity, with amino acid sequences containing COOH-terminal. Another tachykinin has neurokinin A-like immunoreactivity with 23 amino acid residues. There is a partial structural similarity to mammalian peptides.

Angiotensin II (ANG-II) relaxation is an endothelium-dependent mechanism, which is initiated by the release of prostanoids. ANG-II relaxation is vessel-specific and in vivo. It possesses pressor activity and prevents hypotension. This relaxation is a significant feature of trout conductance and capacitance vessels.

The gut of the elasmobranch fish, Scyliorhinus canicula, reveals tachykinins, scyliorhinin I and II, which are observed between the peptides and the amphibian tachykinins physalaemin and (Glu2,Pro5)kassinin. Association is also noted between mammalian tachykinins and tachykinins separated from the brains of teleost fish. Trout intestine shows substance P and neurokinin A (NKA) associated peptides which vary from mammalian peptides by three and two amino acids, respectively. They are duplicates of tachykinins in trout brain.

A single transit through the gill vasculature of an unanesthetized trout is used in the qualification of atrial natriuretic peptide (I 125-ANP) extraction from plasma. The Co-80 EDTA is measured after 1 hour of I 125-ANP along with the determination of the tissue distribution. The measurements insdicated the existence of I 125 bolus injected into the trout is depleted from th blood circulation before 2 minutes. These indicate that the gills are the one of the main places where the ANP is removed from the ciruclation.

Hypoxic vasoconstriction of cyclostome systemic vessels: the antecedent of hypoxic pulmonary vasoconstriction? Am J Physiol Regulatory Integrative Comp Physiol 280: R198-R206, 2001.--Hypoxic vasoconstriction (HV) is an intrinsic response of mammalian pulmonary vascular smooth muscle (VSM). In the present study, HV was examined by myography of vessel rings from three primitive vertebrates: New Zealand hagfish (NZH), Pacific hagfish (PH), and sea lamprey (SL). Hypoxia dilated pre-gill arteries (ventral aorta, afferent branchial) from all species, whereas it contracted systemic arteries [dorsal aorta (DA), efferent branchial, celiacomesenteric]. DA HV was reproducible over several days, and it could be sustained in NZH for 8 h without adverse effects. Tension was proportional to [PO.sub.2], and half-maximal HV was obtained at [PO.sub.2] (mmHg) of 4.7 [+ or -] 0.2 (NZH), 0.8 [+ or -] 0.1 (PH), and 10.7 [+ or -] 1.9 (SL). HV did not require preconditioning (preexisting contractile stimulus) and was unaffected by elevated extracellular potassium (200 mM NZH; 80 mM SL); removal of the endothelium (NZH); or inhibitors of cyclooxygenase, lipoxygenase, cytochrome P-450 or antagonists of [Alpha]-adrenergic, muscarinic, nicotinic, purinergic, or serotoninergic receptors. These results show that HV is an intrinsic feature of systemic VSM in cyclostomes and suggest that HV has been in the repertoire of VSM responses, since the origin of vertebrates. The exceptionally hardy HV in cyclostome DA may provide a useful model with which to examine both the phylogeny and mechanisms of this response. vascular smooth muscle; hagfish; lamprey

Hoagland, Todd M., Leroy Weaver, Jr., J. Michael Conlon, Yugi Wang, and Kenneth R. Olson. Effects of endothelin-1 and homologous trout endothelin on cardiovascular function in rainbow trout. Am. J. Physiol. Regulatory Integrative Comp. Physiol. 278: R460-R468, 2000.--The cardiovascular effects of endothelin (ET)-1 and the recently sequenced homologous trout ET were examined in unanesthetized trout, and vascular capacitance curves were constructed to evaluate the responsiveness of the venous system to ET-1. A bolus dose of 667 pmol/kg ET-1 doubled ventral aortic pressure; produced a triphasic pressor-depressor-pressor response in dorsal aortic pressure ([P.sub.DA]); increased central venous pressure, gill resistance, and systemic resistance; and decreased cardiac output, heart rate, and stroke volume. These responses were dose dependent. Bolus injection of trout ET (333 or 1,000 pmol/kg) produced essentially identical, dose-dependent cardiovascular responses as ET-1. Dorsal aortic infusion of 1 and 3 pmol [multiplied by] [kg.sup.-1] [multiplied by] [min.sup.-1] ET-1 and central venous infusion into the ductus Cuvier of 0.3 and 1 pmol [multiplied by] [kg.sup.-1] [multiplied by] [min.sup.-1] produced similar dose-dependent cardiovascular responses, although the increase in [P.sub.DA] became monophasic. The heightened sensitivity to central venous infusion was presumably due to the more immediate exposure of the branchial vasculature to the peptide. Infusion of 1 pmol [multiplied by] [kg.sup.-1] [multiplied by] [min.sup.-1] ET-1 decreased vascular compliance but had no effect on unstressed blood volume. These results show that ETs affect a variety of cardiovascular functions in trout and that branchial vascular resistance and venous compliance are especially sensitive. The multiplicity of effectors stimulated by ET suggests that this peptide was extensively integrated into cardiovascular function early on in vertebrate phylogeny. fish; vascular capacitance; unstressed blood volume; mean circulatory filling pressure

Wang, Yuqi, Kenneth R. Olson, Michael P. Smith, Michael J. Russell, and J. Michael Conlon. Purification, structural characterization, and myotropic activity of endothelin from trout, Oncorhynchus mykiss. Am. J. Physiol. 277 (Regulatory Integrative Comp. Physiol. 46): R1605-R1611, 1999.--Endothelin (ET) from a nontetrapod species has never been characterized, either structurally or biologically. A single molecular form of trout ET with 21-amino-acid residues was isolated in pure form from an extract of the kidney of the steelhead trout, Oncorhynchus mykiss and its primary structure established as Cys-Ser-Cys-Ala-Thr-Phe-Leu-Asp-Lys -[Glu.sup.10]-Cys-Val-Tyr-Phe-Cys-His-Leu-Asp-Ile-[Ile.sup.20]-Trp. This ammo acid sequence shows only three substitutions ([Ala.sup.4] [right arrow] Ser, [Thr.sup.5] [right arrow] Ser, and [Phe.sup.6] [right arrow] Trp) compared with human ET-2, demonstrating that the structure of the peptide has been well conserved during evolution and that the pathway of posttranslational processing of preproendothelin in the trout is probably similar to that in mammals. Synthetic trout ET produced concentration-dependent constrictions of isolated rings of vascular tissue from trout efferent branchial artery (EBA; [pD.sub.2] = 7.90 [+ or -] 0.06, n = 5), caeliacomesenteric artery ([pD.sub.2] = 8.03 [+ or -] 0.04, n = 4), anterior cardinal vein (ACV; [pD.sub.2] = 8.57 [+ or -] 0.25, n = 4), and rat abdominal aorta (AO; [pD.sub.2] = 8.86 [+ or -] 0.08, n = 7). Trout and rat vessels were more sensitive to mammalian ET-1 than to trout ET ([pD.sub.2] for human ET-1 in: EBA = 9.12 [+ or -] 0.14; ACV = 9.90 [+ or -] 0.15; AO = 8.86 [+ or -] 0.08), but there was no significant difference in the maximum tension produced by either peptide in these vessels. teleost; rat; vasoconstrictor; peptide synthesis

Intracellular and extracellular calcium utilization during hypoxic vasoconstriction of cyclostome aortas. Am J Physiol Regulatory Integrative Comp Physiol 281: R1506-R1513, 2001.--Hypoxic vasoconstriction (HV) is an intrinsic response of mammalian pulmonary and cyclostome aortic vascular smooth muscle. The present study examined the utilization of calcium during HV in dorsal aortas (DA) from sea lamprey and New Zealand hagfish. HV was temporally correlated with increased free cytosolic calcium ([Ca.sup.2+.sub.c]) in lamprey DA. Extracellular calcium ([Ca.sup.2+.sub.o]) did not contribute significantly to HV in lamprey DA, but it accounted for 38.1 [+ or -] 5.3% of HV in hagfish DA. Treatment of lamprey DA with ionomycin, ryanodine, or caffeine added to thapsigarginreduced HV, whereas HV was augmented by BAY K 8644. Methoxyverapamil (D600) in zero [Ca.sup.2+.sub.o] did not affect HV in lamprey DA, nor did it prevent further constriction when [Ca.sup.2+.sub.o] was restored during hypoxia in hagfish DA. Removal of extracellular sodium ([Na.sup.+.sub.o]) caused a constriction in both species. Lamprey DA relaxed to prehypoxic tension following return to normoxia in zero [Na.sup.+.sub.o], whereas relaxation was inhibited in hagfish DA. Relaxation following HV was inhibited in lamprey DA when [Na.sup.+.sub.o] and [Ca.sup.2+.sub.o] were removed. These results show that HV is correlated with [Ca.sup.2+.sub.c] in lamprey DA and that [Na.sup.+]/[Ca.sup.2+] exchange is used during HV in hagfish but not lamprey DA. Multiple receptor types appear to mediate stored intracellular calcium release in lamprey DA, and L-type calcium channels do not contribute significantly to constriction in either cyclostome. vascular smooth muscle; hagfish; lamprey