Enzymatic formation of angiotensins II and III in the hindlimb circulation of dogs

Experiments were performed in 14 anesthetized dogs to (1) to determine if the reductions in hindlimb blood flow produced by [des-Asp1] angiotensin I were due to its local enzymatic (kininase II) conversion to angiotensin III and (2) to quantitate the extent of conversion of angiotensin I to angiotensin II and of [des-Asp1] angiotensin I to angiotensin III in the hindlimb circulation. Graded doses of these peptides were administered as bolus injections directly into the left external iliac artery while measuring flow in this artery electromagnetically. Dose-response relationships were determined before and during the inhibition of kininase II activity with captopril or antagonism of angiotensin receptor sites with [Ile7] angiotensin III. Captopril inhibited the vasoconstrictor responses to angiotensin I and [des-Asp1] angiotensin I, but did not affect the responses to angiotensins II or III, or norepinephrine. [Ile7] angiotensin III inhibited the vasoconstrictor responses to all four angiotensin peptides but did not alter the responses to norepinephrine. These findings indicate that the hindlimb vasoconstrictor responses to [des-Asp1] angiotensin I were due to the local formation of angiotensin III. The extent of conversion of [des-Asp1] angiotensin I to angiotensin III that occurred in one transit through the hindlimb arterial circulation was estimated to be 36.7%, which was not different from the estimated 36.4% conversion of angiotensin I to angiotensin II. We conclude that angiotensin I and [des-Asp1] angiotensin I are converted to their respective vasoactive forms (angiotensins II and III) to a similar extent in the hindlimb circulation via the action of kininase II.     

Actions of angiotensin peptides on the rabbit pulmonary artery

The presence of the angiotensin AT1A-like receptor subtype in the pulmonary artery and AT1B-like receptor subtype in the pulmonary trunk of the rabbit has been reported in two earlier studies. The present study further investigated these receptor subtypes using five other angiotensins (namely angiotensin II, angiotensin III, angiotensin IV, angiotensin-(1-7) and angiotensin-(4-8)). The direct action of the angiotensins on the rabbit pulmonary arterial and trunk sections and the ability of each angiotensin to further contract or relax preconstricted sections of the pulmonary artery and trunk were studied using the organ bath set-up. The effects of angiotensin III on the 3H overflow from re-uptaken [3H]noradrenaline in the electrically-contracted rabbit pulmonary arterial and trunk sections were also studied. The contractile response of the arterial and trunk section had the following rank order potency: angiotensin II > angiotensin III > angiotensin IV. The contractile response to these angiotensins was greatly reduced or absent in the pulmonary trunk. Angiotensin II further contracted the preconstricted arterial and trunk sections. In contrast, angiotensin III further contracted the preconstricted arterial section but relaxed the preconstricted trunk section. Angiotensin IV similarly relaxed the preconstricted trunk section but had minimum effect on the preconstricted arterial section. Angiotensin-(1-7) and angiotensin-(4-8) had no effect on both sections. The actions of the three angiotensins were inhibited by losartan, an AT1-selective antagonist. Indomethacin, a cyclo-oxygenase inhibitor, inhibited the relaxation caused by angiotensin III and angiotensin IV in the trunk section. The effects of angiotensin III on the electrically preconstricted sections of the pulmonary trunk and artery were not accompanied by any significant changes in 3H overflow. The differential responses produced by angiotensin II and its immediate metabolites via two positionally located and functionally opposing receptor subtypes suggest that the pulmonary trunk and artery is not a passive conduit but an important regulator of blood flow from the heart to the lung.     

Central hypertensive actions of angiotensin I, II and III in conscious rats

The effects of intracerebroventricular administrations of three natural angiotensins, angiotensin I (ANG I 3.8 X 10-11-9.4 X10-10 mol/kg body weight), II (9.6 X 10-12-2.4 X 10-10 mol/kg body weight) and III (2.7 X 10-10 2.5 X 10-9 mol/kg body weight) on systemic blood pressure were investigated in conscious rats. Angiotensin II (ANG II), ANG I and angiotensin III (ANG III), increased blood pressure in a dose-related manner. The order of potency of angiotensins was ANG II greater than ANG I greater than ANG III. The intraventricular administration of a converting enzyme inhibitor (SQ 14225, 6.9 X10-8 mol/kg) abolished the central effect of ANG I, while an angiotensin II analogue ([Sar1-Ala8]ANG II, 1.1 X 10-8 mol/kg) administered intraventricularly inhibited the central pressor effects of these three angiotensins. These results suggest that ANG II is a main mediator of the renin-angiotensin system in the central nervous system.     

Angiotensin III and IV activation of the brain AT1 receptor subtype in cardiovascular function

The present investigation determined that native angiotensins II and III (ANG II and III) were equipotent as pressor agents when ICV infused in alert rats, whereas native angiotensin IV (ANG IV) was less potent. An analogue of each of these angiotensins was prepared with a hydroxyethylamine (HEA) amide bond replacement at the N-terminus, yielding additional resistance to degradation. These three angiotensin analogues, HEA-ANG II, HEA-ANG III, and HEA-ANG IV, were equivalent with respect to maximum elevation in pressor responses when ICV infused; and each evidenced significantly extended durations of effect compared with their respective native angiotensin. Comparing analogues, HEA-ANG II had a significantly longer effect compared with HEA-ANG III, and HEA-ANG IV, whereas the latter were equivalent. Pretreatment with the AT₁ receptor subtype antagonist, Losartan (DuP753), blocked subsequent pressor responses to each of these analogues, suggesting that these responses were mediated by the AT₁ receptor subtype. Pretreatment with the specific AT₄ receptor subtype antagonist, Divalinal (HED 1291), failed to influence pressor responses induced by the subsequent infusion of these analogues. These results suggest an important role for Ang III, and perhaps ANG IV, in brain angiotensin pressor responses mediated by the AT₁ receptor subtype.     

Comparative responses to alpha,beta-methylene-ATP in cat pulmonary, mesenteric, and hindquarter vascular beds.

Responses to the P2X-purinoceptor agonist alpha,beta-methylene-ATP (alpha,beta-MeATP) were investigated in the pulmonary, hindquarter, and mesenteric vascular beds in the cat. Under constant-flow conditions, injections of alpha,beta-MeATP caused dose-related increases in perfusion pressure in the pulmonary and hindquarter beds and a biphasic response in the mesenteric circulation. In the pulmonary vascular bed, the order of potency was alpha,beta-MeATP > U-46619 > angiotensin II, whereas, in the hindquarters, the order of potency was angiotensin II > U-46619 > alpha,beta-MeATP. The order of potency was similar in the hindquarter and mesenteric beds when the pressor component of the response to alpha,beta-MeATP was compared with responses to angiotensin II and U-46619. The P2X-receptor antagonist pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid attenuated the pressor response to alpha,beta-MeATP in the hindquarter circulation and the pressor component in the mesenteric vascular bed. Pressor responses to alpha,beta-MeATP were not altered by cyclooxygenase, alpha-adrenergic, or angiotensin AT(1) antagonists. These data show that alpha,beta-MeATP has potent pressor activity in the pulmonary circulation, where it was 100-fold more potent than angiotensin II. In contrast, alpha,beta-MeATP had modest pressor activity in the systemic bed, where it was 1,000-fold less potent than angiotensin II. These data suggest that responses to alpha,beta-MeATP are dependent on the vascular bed studied and may be dependent on the density of P2X receptors in the vascular bed.     

Tumor promoter 12-O-tetradecanoylphorbol 13-acetate inhibits mas/angiotensin receptor-stimulated inositol phosphate production and intracellular Ca2+ elevation in the 401L-C3 neuronal cell line

Stimulation of mas-oncogene transfected 401L-C3 cells by angiotensins leads to the production of inositol phosphates. This response shows dose dependence, and has an apparent rank order of potency angiotensin III greater than or equal to angiotensin II much greater than angiotensin I. Preincubation with 12-O-tetradecanoylphorbol 13-acetate, for 5 min, significantly diminishes both inositol phosphate and intracellular [Ca2+] responses to angiotensins, without affecting those stimulated by the endogenous bradykinin receptor. Incubation of 401L-C3 cells with either phorbol ester or angiotensins leads to elevation of intracellular pH, implying that mas/angiotensin receptor stimulation itself leads to protein kinase C activation. These results suggest the operation of a negative feedback loop specific for the mas/angiotensin receptor signalling pathway, and which may be essential in defining the final biological output response to this receptor stimulation.     

Steroids as potential modulators of angiotensin receptors in bovine adrenal glomerulosa and kidney

To test the hypothesis that there is feedback inhibition of adrenal angiotensin receptors by substances released in response to the peptides, we measured binding of labeled angiotensins in the presence of various steroids. Approximately half of the 70 steroids tested inhibited binding of labeled angiotensin II and III to intact and broken cells from bovine adrenal glomerulosa and kidney, but the concentrations required for inhibition were relatively high. The most potent inhibitors were 3 alpha, 5 beta tetrahydroaldosterone and tetrahydrodeoxycorticosterone (ID50 = 8 x 10-5 M). Kinetic analysis showed that inhibition was mostly competitive. among steroids whose reduced congeners were tested, potency increased in the sequence: parent steroid less than 5 alpha dihydroderivative less than 5 beta dihydro derivative less than 3 alpha, 5 beta tetrahydro-derivative. Tetrahydrodeoxycorticosterone inhibited aldosteronogenesis by intact cells at concentrations that inhibited angiotensin binding. Steroids differentially inhibited binding of labeled angiotensins in II and III, and discriminated between receptors in adrenal glomerulosa and kidney. The results provide additional evidence for heterogeneity of angiotensin receptors, and lead to the prediction that any normal or pathological inhibition of angiotensin receptors by steroids will be mediated by reduced derivatives.     

Heptapeptide analogues induce greater blockade of renal than femoral vascular responses to angiotensin

We characterized blockade induced by 2 octapeptide and 2 heptapeptide analogues of angiotensin in the vascular beds of the kidney and hindlimb. Bolus injections of angiotensin II and its 1-des Asp analogue (angiotensin III) at the dose which reduced blood flow by about 50 percent and graded infusions of the analogue-antagonists were made directly into each artery and flow responses were measured with an electromagnetic flowmeter in the anesthetized dog. With the dose of antagonist which produced 50 percent inhibition of the control angiotensin response (ID 50) as the index, inhibition was slightly greater in the kidney than in the hindlimb for both the potent octapeptide antagonist {1-Sar, 8-Ala angiotensin II: kidney ID 50 = 15.3±1.7 (SD) ng/kg/min; hindlimb ID 50 = 23.3±1.8 (SD) ng/kg/min} and the weak octapeptide antagonist {1-D-Asn, 8-Ala angiotensin II: kidney ID 50 = 178.7±2.0 (SD) ng/kg/min; hindlimb ID 50 = 266.7±1.9 (SD) ng/kg/min}. In contrast, both the potent and weak heptapeptide analogues were much more effective as antagonists in the renal than the femoral vascular bed {1-des Asp, 8-Ile AII: kidney ID 50 = 14.9±1.8 (SD) ng/kg/min; hindlimb ID 50 = 36.2±1.9 (SD) ng/kg/min}; {1-des Asp, 8-Ala angiotensin II: kidney ID 50 = 408.9±1.8 (SD) ng/kg/min; hindlimb ID 50 = 1270±2.8 (SD) ng/kg/min}. The difference in the influence of the analogues in the two vascular beds may reflect either a difference in their angiotensin receptors or in the rate at which heptapeptide analogues are degraded in their transit through the renal and femoral vasculature.     

Angiotensin II indirectly vasoconstricts the ovine uterine circulation

The uterine vasculature of women and sheep predominantly expresses type 2 ANG II receptors that do not mediate vasoconstriction. Although systemic ANG II infusions increase uterine vascular resistance (UVR), this could reflect indirect mechanisms. Thus we compared systemic and local intra-arterial ANG II infusions in six near-term pregnant and five ovariectomized nonpregnant ewes to determine how ANG II increases UVR. Systemic ANG II dose-dependently (P > 0.001) increased arterial pressure (MAP) and UVR and decreased uterine blood flow (UBF) in pregnant and nonpregnant ewes; however, nonpregnant responses exceeded pregnant (P < 0.001). In contrast, local ANG II infusions at rates designed to achieve concentrations in the uterine circulation comparable to those seen during systemic infusions did not significantly decrease UBF in either group, and changes in MAP and UVR were absent or markedly attenuated. When MAP rose during local ANG II, which only occurred with doses > or =2 ng/ml, increases in MAP were delayed more than twofold compared with responses during systemic ANG II infusions and always preceded decreases in UBF, resembling that observed during systemic ANG II infusions. These observations demonstrate attenuated uterine vascular responses to systemic ANG II during pregnancy and suggest that systemic ANG II may increase UVR through release of another potent vasoconstrictor(s) into the systemic circulation.     

Angiotensin III as well as angiotensin II regulates water flow through aquaporins in a clam worm

Angiotensin III has been reported to exist in various animals and tissues. The physiological role, however, is still unclear except that brain angiotensin III is a central regulator of vasopressin release. In this study, angiotensin III as well as angiotensin II enhanced an increase in body weight of clam worms of Perinereis sp. under a hypo-osmotic condition and suppressed a decrease in body weight under a hyper-osmotic condition. When clam worms were treated with tetrachloroaurate (III) after angiotensin-treatment, these enhancing and suppressive effects of the angiotensins under hypo- and hyper-osmotic conditions were inhibited. In contrast, when clam worms were pretreated with tetrachloroaurate (III) before angiotensin-treatment, these effects of angiotensins were not inhibited. Since tetrachloroaurate (III) is a representative blocker of aquaporins, these results indicate that angiotensin III as well as angiotensin II regulates water flow through aquaporins in clam worms.     

Differential effects of PACAP and VIP on the pulmonary and hindquarters vascular beds of the cat.

Responses to pituitary adenylate cyclase-activating polypeptide (PACAP), a novel peptide derived from ovine hypothalamus with 68% sequence homology with vasoactive intestinal polypeptide (VIP), were investigated in the pulmonary and hindquarters vascular beds of the anesthetized cat under conditions of controlled blood flow. Injection of the peptide into the perfused lung lobe under elevated tone conditions produced dose-dependent decreases in lobar arterial pressure that were accompanied by biphasic changes in systemic arterial pressure characterized by an initial decrease followed by a secondary increase in pressure. When compared with other vasodilator agents in the pulmonary vascular bed, the relative order of potency was isoproterenol greater than PACAP greater than acetylcholine greater than calcitonin gene-related peptide greater than VIP. In the hindquarters vascular bed, intra-arterial injections of PACAP produced biphasic changes in hindquarters perfusion pressure characterized by initial decreases followed by secondary increases, which were accompanied by biphasic changes in systemic arterial pressure. In terms of relative vasodilator activity in the hindlimb, the order of relative potency was isoproterenol greater than acetylcholine greater than calcitonin gene-related peptide greater than VIP greater than PACAP. PACAP was the only agent that caused a secondary vasoconstrictor response in the hindlimb and produced biphasic changes in systemic arterial pressure. D-Phe2-VIP, a VIP receptor antagonist, blocked the hindquarters vasodilation in response to VIP but had no effect on responses to PACAP. The present investigation shows that PACAP produces pulmonary vasodilation, as well as dilation, and vasoconstriction in the systemic (hindlimb) vascular bed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Differential effects of losartan and candesartan on vasoconstrictor responses in the rat

Losartan has been reported to have inhibitory effects on thromboxane (TP) receptor-mediated responses. In the present study, the effects of 2 nonpeptide angiotensin II (AT1) receptor antagonists, losartan and candesartan, on responses to angiotensin II, the thromboxane A2 mimic, U46619, and norepinephrine were investigated and compared in the pulmonary and systemic vascular beds of the intact-chest rat. In this study, intravenous injections of angiotensin II, U46619, and norepinephrine produced dose-related increases in pulmonary and systemic arterial pressure. Losartan and candesartan, in the doses studied, decreased or abolished responses to angiotensin II. Losartan, but not candesartan, and only in a higher dose, produced small, but statistically significant, reductions in pressor responses to U46619 and to norepinephrine in the pulmonary and systemic vascular beds. Furthermore, losartan significantly reduced arachidonic acid-induced platelet aggregation, whereas candesartan had no effect. Pressor responses to angiotensin II were not changed by thromboxane and alpha-adrenergic receptor antagonists, or by cyclooxygenase and NO synthase inhibitors. These results show that losartan and candesartan are potent selective AT1 receptor antagonists in the pulmonary and systemic vascular beds and that losartan can attenuate thromboxane and alpha-adrenergic responses when administered at a high dose, whereas candesartan in the highest dose studied had no effect on responses to U46619 or to norepinephrine. The present data show that the effects of losartan and candesartan on vasoconstrictor responses are different and that pulmonary and systemic pressor responses to angiotensin II are not modulated or mediated by the release of cyclooxygenase products, activation of TP receptors, or the release of NO in the anesthetized rat.     

Effects of angiotensins on cellular hypertrophy and c-fos expression in cultured arterial smooth muscle cells.

An increase in cell size and protein content was observed when quiescent arterial smooth muscle cells in culture were incubated with either angiotensin II or III. These effects were inhibited by the specific angiotensin type-1 receptor antagonist losartan (DuP753) but not by CGP42112A. In parallel, a transient and dose-dependent induction of c-fos was demonstrated not only with angiotensins II and III but also with angiotensin I. Both angiotensins II and III exerted their maximal effect at 1 microM, while angiotensin I needed a tenfold-higher concentration to exert an identical effect. As for hypertrophy, losartan also inhibits angiotensin-induced c-fos expression, suggesting that this gene may be involved into the hypertrophic process. Angiotensin-I-mediated c-fos induction is partially inhibited by the angiotensin-converting enzyme inhibitors captopril and trandolaprilate; given that an angiotensin-converting enzyme activity was detected in these smooth muscle cell cultures, these results suggest that angiotensin-I-induced c-fos expression is mediated in part via angiotensin-I conversion to angiotensin II, but also by other unidentified pathway(s). Angiotensin I could essentially induce smooth muscle cell hypertrophy by indirect mechanisms, while angiotensins II and III act directly on smooth muscle cells.     

Monophasic and biphasic effects of angiotensin II and III on norepinephrine uptake and release in rat adrenal medulla.

Angiotensin II and III have hypertensive effects. They induce vascular smooth muscle constriction, increase sodium reabsorption by renal tubules, stimulate the anteroventral third ventricle area, increase vasopressin and aldosterone secretions, and modify catecholamine metabolism. In this work, angiotensin II and III effects on norepinephrine uptake and release in rat adrenal medulla were investigated. Both angiotensins decreased total and neuronal norepinephrine uptake. Angiotensin II showed a biphasic effect only on evoked neuronal norepinephrine release (an earlier decrease followed by a later increase), while increasing the spontaneous norepinephrine release only after 12 min. On the other hand, angiotensin III showed a biphasic effect on evoked and spontaneous neuronal norepinephrine release. Both angiotensins altered norepinephrine distribution into intracellular stores, concentrating the amine into the granular pool and decreasing the cytosolic store. The results suggest a physiological biphasic effect of angiotensin II as well as angiotensin III that may be involved in the modulation of sympathetic activity in the rat adrenal medulla.     

Formation of angiotensin III by angiotensin-converting enzyme.

Angiotensin III is formed from des-Asp1 -angiotensin I by angiotensin-converting enzyme. The Km (11 muM) of the reaction is one-third of that for the conversion of angiotensin I into angiotensin II. As suggested by the Km values, bradykinin, peptide BPP9a and angiotensins II and III are better inhibitors of the formation of angiotensin II than of the formation of angiotensin III.     

Estrogen modulation of angiotensin-stimulated phosphoinositide hydrolysis in slices of rat anterior pituitary

In this study, slices of rat anterior pituitary were prelabeled with [³H]myo-inositol and the ability of angiotensins II and III to stimulate [³H]phosphoinositide hydrolysis was characterized. When using tissue derived from ovariectomized rats, dose-response experiments revealed that angiotensin II significantly increases [³H]inositol monophosphate formation (in the presence of 10 mM LiCI) at concentrations of 10 nM and above. Maximal stimulation by angiotensin II was observed at 1 μM (228% of basal) and 50% maximal stimulation was at 10.8 ± 2.7 nM. Angiotensin III was less potent when compared to angiotensin II (maximal stimulation at 10 μM; 220% of basal: 50% maximal stimulation, 475 ± 159 nM). When using normal female rats, significant stimulation by angiotensin II was not observed until 1 μM angiotensin II. When ovariectomized rats were treated for 7 days with 17β-estradiol, increases in [³H]inositol monophosphate induced by 1 μM angiotensin II were significantly reduced when compared to sesame oil vehicle controls.This study shows that estrogen down-regulates angiotensin receptor coupling in the anterior pituitary. Moreover, it illustrates the influence of the hormonal state of the animal on the regulation of the effects of angiotensins in this tissue.     

The adrenal and vascular effects of angiotensin II and III in sodium depleted rats

The effects of angiotensin II and angiotensin III on mean arterial pressure, serum aldosterone, and serum corticosterone were studied in normal and sodium depleted, conscious rats. In normal rats, angiotensin III was 76% (p > 0.10) as potent as angiotensin II on aldosterone release but only 31% (p < 0.001) as potent on blood pressure. Following sodium depletion, the pressor responses to both angiotensin II and III were reduced (p < 0.001) (65% and 86% respectively). In addition, the release of aldosterone by both peptides was potentiated by sodium depletion as indicated by an increase in the slope of the dose-response curves. However, in the sodium depleted rats, angiotensin III was only 20% (p < 0.001) as potent as angiotensin II in stimulating aldosterone release. Small changes in serum corticosterone were noted following infusions of both peptides, but unlike the case with aldosterone, sodium depletion did not alter the serum corticosterone responses to the peptides. These $\text{in}$$\text{vivo}$ experiments taken with $\text{in}$$\text{vitro}$ studies support the interpretation that angiotensin III could function to control aldosterone release in altered sodium states either as a circulating hormone if present in concentrations far in excess of those of angiotensin II or as a local hormone formed in the adrenal from angiotensin II.     

Vasopressin and angiotensin II stimulate oxygen uptake in the perfused rat hindlimb

Vasopressin and angiotensin II markedly stimulated oxygen uptake in the perfused rat hindlimb. The increase due to each agent approached 70% of the basal rate, and was greater than that produced by a maximal concentration of norepinephrine. Half-maximal stimulation occurred at 60 pM vasopressin, 0.5 nM angiotensin II and 10 nM norepinephrine. Angiotensins I and III were less potent than angiotensin II. For each agent, the dose-dependent increase in oxygen uptake coincided with a dose-dependent increase in perfusion pressure. The effects of both vasopressin and angiotensin to increase oxygen uptake and pressure were not inhibited by either phentolamine, propranolol or a combination of the two, but were completely inhibited by the vasodilator, nitroprusside. Nitroprusside also inhibited flow-induced increases in hindlimb oxygen uptake and perfusion pressure. The findings indicate a key role for the vascular system in the control of hindlimb oxygen uptake.     

Effects of PKC isozyme inhibitors on constrictor responses in the feline pulmonary vascular bed

The effects of G?-6976, a Ca(2+)-dependent protein kinase C (PKC) isozyme inhibitor, and rottlerin, a PKC-delta isozyme/calmodulin (CaM)-dependent kinase III inhibitor, on responses to vasopressor agents were investigated in the feline pulmonary vascular bed. Injections of angiotensin II, norepinephrine (NE), serotonin, BAY K 8644, and U-46619 into the lobar arterial constant blood flow perfusion circuit caused increases in pressure. G?-6976 reduced responses to angiotensin II; however, it did not alter responses to serotonin, NE, or U-46619, whereas G?-6976 enhanced BAY K 8644 responses. Rottlerin reduced responses to angiotensin II and NE, did not alter responses to serotonin or U-46619, and enhanced responses to BAY K 8644. Immunohistochemistry of feline pulmonary arterial smooth muscle cells demonstrated localization of PKC-alpha and -delta isozymes in response to phorbol 12-myristate 13-acetate and angiotensin II. Localization of PKC-alpha and -delta isozymes decreased with administration of G?-6976 and rottlerin, respectively. These data suggest that activation of Ca(2+)-dependent PKC isozymes and Ca(2+)-independent PKC-delta isozyme/CaM-dependent kinase III mediate angiotensin II responses. These data further suggest that Ca(2+)-independent PKC-delta isozyme/CaM-dependent kinase III mediate responses to NE. A rottlerin- or G?-6976-sensitive mechanism is not involved in mediating responses to serotonin and U-46619, but these PKC isozyme inhibitors enhanced BAY K 8644 responses in the feline pulmonary vascular bed.     

Potent cardiovascular effects of homologous urotensin II (UII)-related peptide and UII in unanesthetized eels after peripheral and central injections

We cloned cDNAs encoding urotensin II (UII)-related peptide (URP) and UII in Japanese eel, Anguilla japonica, the former being the first such cloning in teleost fishes. Unlike the exclusive expression of UII in the urophysis, the URP gene was expressed most abundantly in the brain (medulla oblongata) followed by the urophysis. Peripheral injections of URP into eels increased blood pressure by 16.1 ± 0.8 mmHg at 0.1 nmol/kg in ventral aortic blood pressure (P(VA)) and with similar potency and efficacy to that of UII (relative potency of URP to UII = 0.83). URP/UII and ANG II preferentially acted on the branchial and systemic circulations, respectively, and the duration of effect was distinct among the three peptides in the order of UII (60 min) >URP (30 min) >ANG II (14 min) in P(VA). Urantide, a mammalian UII receptor antagonist, inhibited the URP effect (-63.6 ± 5.2%) to a greater extent than for UII (-39.9 ± 5.0%). URP and UII constricted isolated eel branchial and systemic arteries, showing their direct actions on the vascular smooth muscle. Central injection of URP increased blood pressure by 12.3 ± 0.8 mmHg at 50 pmol/eel in P(VA) and with similar efficacy but less potency (relative potency = 0.47) and shorter duration compared with UII. The central actions of URP/UII were more potent on the branchial circulation than on the systemic circulation, again opposite the effects of ANG II. The similar responses to peripheral and central injections suggest that peripheral hormones may act on the brain. Taken together, in eels, URP and UII are potent cardiovascular hormones like ANG II, acting directly on the peripheral vasculature, as well as a central vasomotor site, and their actions are mediated to different degrees by the UII receptor.