Effect of intrathecal administration of ET-1, ET-3 and ET(16–21) on blood pressure and micturition reflex in anesthetized rats

In urethane-anesthetized rats, intrathecal administration of endothelin-1 (ET-1), endothelin-3 (ET-3) (3–100 pmol/rat) or the C-terminal hexapeptide ET(16–21) (10–100 nmol/rat) dose-dependently increased mean blood pressure (MBP) and suppressed the supraspinal micturition reflex (SMR). ET(16–21), at 100 nmol, produced a pressor response comparable to that induced by ET-1 at 100 pmol.

Guanethidine and hexamethonium pretreatment significantly reduced the increase of MBP induced by ET-1 but was inactive in antagonizing inhibition of SMR. Neither naloxone nor adrenalectomy were effective in preventing the responses to ET-1.

The high degree of lethality (60–100%), observed with ET-1 (10–100 pmol), was not reduced by guanethidine, naloxone, adrenalectomy or by hexamethonium.

ET-3, at 100 pmol or 1 nmol, induced death in about 50% of cases. The symptoms before death were reduction of the respiratory rate followed by respiratory arrest.

These findings indicate that the pressor response to intrathecally-administered endothelins involves activation of sympathetic preganglionic elements; induction of secretion of catecholamines from adrenal glands was excluded.

Lethality and inhibition of SMR does not involve opioids, sympathetic activation or release of catecholamines from the adrenal glands.     

Phosphoramidon potentiates the endothelin-1-induced bronchopulmonary response in guinea-pigs

We investigated the effect of the endopeptidase-inhibitor, phosphoramidon, on the bronchopulmonary response induced by endothelin-1 in vivo or in isolated perfused lungs. In vivo aerosol administration of 1 or 3 μg/ml endothelin-1 for 2 min provoked no significant bronchopulmonary response. When awake animals were pretreated by an aerosol of phosphoramidon (0.1 mM, for 15 min), the bronchopulmonary response induced by 1 and 3 μg/ml endothelin-1 was markedly enhanced. In isolated guinea-pig lungs, aerosol administration of endothelin-1 (3 μg/ml, for 2 min) evoked a low increase in pulmonary inflation pressure. Treatment of awake animals with an aerosol of phosphoramidon before lung recollection led to a significant potentiation of the endothelin-1-induced increase in pulmonary inflation pressure. These results demonstrate that phosphoramidon potentiates the in vivo and in vitro bronchopulmonary response evoked by low doses of endothelin-1 and suggest that endopeptidase-like enzymes present in the airway tissue modulate the effect of the peptide.     

Cardiovascular effects of dynorphin A (1–13) in conscious rats and its modulation of morphine bradycardia over time

The short-term cardiovascular effects of dynorphin A (1–13), as well as its effects upon morphine bradycardia were investigated. In unanesthetized, unrestrained rats, intracerebroventricular (ICV) dynorphin A (1–13) injections (10–20 μg) produced a dose-related pressor effect, whereas intravenous (IV) dynorphin A (1–13) (1.0 mg/kg) produced a depressor effect; these responses persisted less than five min. Heart rate was not significantly altered by these doses or routes of administration. Dynorphin A (1–13) also produced behavioral effects in the unanesthetized animals, such as wet dog shakes in response to IV administration and wet dog shakes accompanied by barrel rolling in response to ICV administration. To evaluate the effects of dynorphin A (1–13) pretreatment on the bradycardic response to IV morphine, rats were pretreated with 10 μg dynorphin A (1–13) ICV four, six or eight hours prior to challenge with morphine sulfate (0.1 mg/kg IV). Four hour pretreatment with dynorphin A (1–13) (tested at 14:00 hr) resulted in a potention of morphine bradycardia, with six hours pretreatment (tested at 16:00 hr) no effect was observed, and eight hours following dynorphin A (1–13) pretreatment (tested at 18:00 hr) morphine bradycardia was attenuated. Additionally, the bradycardic response to IV morphine alone became more exaggerated as rats approached their nocturnal activity cycle. These data further establish that dynorphin A (1–13) exerts a potent, long lasting modulatory effect on morphine bradycardia and emphasize the importance of circadian variables in altering the magnitude of cardiovascular responses to opioid agonists.     

Pharmacological comparison of bPTH-(1–34) and other hypotensive peptides in the dog

The purpose of the present study was to compare the potency, effectiveness and duration of action of synthetic bPTH-(1–34) with those of other known hypotensive peptides in the anesthetized dog. Of sixteen peptides tested in the present study only 8 were demonstrated to possess hypotensive activity. While bPTH-(1–34) was one of the least potent of the hypotensive peptides, it was equal to or greater than the other peptides in terms of effectiveness and duration of action. Of all the peptides studied, substance P and eledoisin were the most potent in terms of their hypotensive action. It is suggested that perhaps substance P and eledoisin might act at a different site or through different mechanisms than do vasoactive intestinal peptide (V.I.P.), corticotropin inhibiting peptide (C.I.P.), neurotensin, xenopsin, bradykinin and bPTH-(1–34).     

Systemic site of action for pressor effect of angiotensin II injected into the fourth cerebral ventricle of rats?

Angiotensin II (ANG II) causes a systemic pressor effect when injected into the cerebral ventricles. In the rat fourth ventricle, the effective doses for the ANG II pressor effect are over 100 times larger than in the systemic circulation. Considering the discrepancy of doses, the possibility that ANG II may reach the systemic circulation and promote pressor effects, following injection into the fourth ventricle, was investigated. The effects on blood pressure of different vasoactive peptides that produce pressor responses when injected into the central nervous system were compared. Dose-response curves were obtained for intravenous or fourth cerebroventricular injections of ANG II, lysyl-vasopressin (LVP), bradykinin (BK), or endothelin-1 (ET-1). The ED50 ratios for intracerebroventricular/intraveneous injections were 110 for ANG II, 109 for LVP, 0.01 for BK, and approximately 0.4 for ET-1. In cross-circulation preparations, pressor responses occurred in the donor rat following injection into the fourth cerebral ventricle of the recipient animal, showing that effective doses of ANG II, administered to the fourth cerebral, reach the systemic circulation. The same results were obtained for the microinjection of 4 nmol of LVP into the fourth cerebral ventricle of recipient animals. High-performance reverse-phase liquid chromatography analyses of arterial blood showed that approximately 1% of the [125I]ANG II injected into the fourth cerebral ventricle may be recovered from the systemic circulation a few seconds after the microinjection. The systemic administration of the ANG II receptor antagonist losartan blocked the response to ANG II injected into the fourth ventricle whereas antagonist administration in the same ventricle did not. Angiotensin injections into the lateral ventricle produced pressor responses that were reduced by antagonist administration to the same ventricle but not by systemic administration of the antagonist. The data suggest that the pressor effect resulting from ANG II or LVP injections into the fourth cerebral ventricle may be due to the action of this peptide in the systemic circulation. On the other hand, the pressor effect due to ANG II microinjection into the lateral ventricle apparently results from the direct stimulation of central periventricular structures.     

Pressor responses to endothelin-1 in normotensive and spontaneously hypertensive rats

In freely moving rats, endothelin-1 (0.0135–4.5 nmol/kg) administered as an intravenous bolus injection, produced an immediate, short-lasting, dose-related fall in blood pressure followed by a long-lasting, dose-related increase in blood pressure. There was a higher sensitivity in the pressor responses to endothelin-1, in spontaneously hypertensive (SH) rats (ED₅₀ = 0.11 ± 0.02 and 0.28 ± 0.02 nmol/kg, in SH and normotensive rats, respectively), but no change in the maximal pressor effect of endothelin-1 in SH rats.

In rat isolated aorta, endothelin-1 induced a greater vasocontractile effect in SH rats than in normotensive rats. In both rat strains, removal of the endothelium did not change the concentration-effect curves obtained in endothelium-intact preparations. These data add further support to the hypothesis that endothelin-1 could play a role in genetic hypertension, at least in the maintenance of high blood pressure.     

Dynorphin(1–13) impairs memory formation for aversive and appetitive learning in chicks

The opioid peptide dynorphin(1–13) impairs memory formation in chicks (5). We examined whether this occurs for both aversively and appetitively motivated learning. Four-day-old chicks were injected with dynorphin(1–13) into the intermediate medial hyperstriatum ventrale and trained on either a peck avoidance (PA) or an appetitive discrimination (AD) task; 2-day-old chicks were trained on PA. In 2-day-old chicks, dynorphin was amnestic for PA at 0.01, 0.03, or 0.1 mM. In 4-day-old chicks, dynorphin impaired memory formation for PA at 0.1 mM, and for AD training at 0.03 mM. Thus, similar doses of dynorphin impair memory formation for both appetitive and aversive conditioning.     

The effect of 4-week streptozotocin-induced diabetes on responses to endothelin-1 in rat isolated atria

The effect of endothelin-1 has been examined on isolated spontaneously beating right atria and electrically driven left atria from diabetic rats and age-matched controls. Diabetes was induced by a single i.v. injection of streptozotocin (65 mg/kg) 4–5 weeks before the experiments. Endothelin-1 (0.01–100 nM) caused concentration-dependent increases in atrial rate and force; the increases were not different between atria from diabetic and control rats. The ability of endothelin-1 to reduce chronotropic and inotropic responses to noradrenaline was also not different between the two groups. Endothelin-1 (10 nM) decreased the chronotropic response to sympathetic nerve stimulation (2 Hz, 10 s) in atria from control rats by 68 ± 5% (n = 8), but this decrease was slightly smaller (45 ± 6%, N = 8) in atria from diabetic rats.

The results provide no evidence to suggest that the diabetic state markedly alters cardiac responses to endothelin-1.     

Vasoactive prostanoids are generated from arachidonic acid by COX-1 and COX-2 in the mouse

Generation of vasoactive prostanoids from arachidonic acid by cyclooxygenase (COX)-1 and COX-2 was investigated in anesthetized mice. Intravenous injections of the prostanoid precursor arachidonic acid increased pulmonary arterial pressure and decreased systemic arterial pressure. Pulmonary pressor and systemic depressor responses were attenuated by SC-560 and nimesulide, inhibitors of COX-1 and COX-2, in doses that did not alter responses to injected prostanoids. Pulmonary pressor responses to arachidonic acid were blocked and a depressor response was unmasked, whereas systemic depressor responses were not altered, by a thromboxane receptor antagonist. Pulmonary and systemic pressor responses to angiotensin II injections and systemic pressor responses to angiotensin II infusion were not modified by COX-1 or COX-2 inhibitors but were attenuated by losartan. Systemic depressor responses to arachidonic acid were smaller in COX-1 and COX-2 knockout mice, whereas responses to angiotensin II, norepinephrine, U-46619, endothelin-1, and PGE(1) were not different in COX-1 and COX-2 knockout and wild-type control mice. These results suggest that vasoactive prostanoids with pulmonary pressor and systemic vasodepressor activity are formed by COX-1 and COX-2 and are consistent with Western blot analysis and immunostaining showing the presence of COX-1 and COX-2. These data suggest that thromboxane A(2) (TxA(2)) is formed from the precursor by COX-1 and COX-2 in the lung and are in agreement with immunofluorescence studies showing thromboxane synthase. The present data suggest that COX-1- or COX-2-derived prostanoids do not modulate responses to angiotensin II or other vasoactive agents and that prostanoid responses are similar in CD-1 and C57BL/6 and in male and female mice.     

Comparative effects on blood pressure and heart rate of dynorphin A(1–13) in anterior hypothalamic area, posterior hypothalamic area, nucleus tractus solitarius, and lateral cerebral ventricle in the rat

The objective of this study was to explore the effects of the endogenous opioid peptide dynorphin A(1–13) on the CNS regulation of blood pressure and heart rate. Wistar rats, anesthetized with pentobarbital and halothane, received dynorphin A(1–13) microinjected into the anterior hypothalamus area (AHA), the posterior hypothalamic area (PHA), the nucleus tractus solitarius (NTS), or the lateral cerebral ventricle (ICV). Dynorphin A(1–13), 20 (12 nmol) or 30 μg ICV, produced significant (p < 0.05) reductions in blood pressure and heart rate. Naloxone, 50 μg/kg ICV, completely prevented the blood pressure response and significantly (p < 0.05) blunted the heart rate response to the highest dynorphin concentration, 30 μg ICV (18 nmol). Dynorphin A(1–13), 5 μg, in the NTS significantly (p < 0.05) decreased systolic and diastolic blood pressure and heart rate with the response being evident 10 min and persisting for 30 min after injection. In contrast, the same dose of dynorphin A(1–13) in the AHA produced an immediate, marked, and significant (p < 0.05) decrease in systolic and diastolic blood pressure and heart rate that attained its maximum 1–3 min and returned rapidly towards baseline levels. Dynorphin A(1–13), 5 or 10 μg in the posterior hypothalamic area, was not associated with any change in blood pressure or heart rate. Injection of the diluent at any site was not associated with any changes in blood pressure or heart rate. The maximum change in blood pressure with dynorphin was greater in the AHA than NTS, and the maximum change in heart rate was greater in the NTS than AHA. These data indicate a potential role for dynorphin as a modulator of the CNS regulation of blood pressure and cardiac rate, and this is mediated in part through different areas in the brain that maybe localized to the anterior hypothalamic area and nucleus tractus solitarius but not the posterior hypothalamic area.     

Inhibition of adrenal steroid metabolism by administration of 1-aminobenzotriazole to guinea pigs

Prior in vitro investigations demonstrated that the P450 suicide substrate, 1-aminobenzotriazole (ABT), was a potent inhibitor of xenobiotic metabolism but had no effect on steroidogenic enzymes in the guinea pig adrenal cortex. Studies were done to determine if ABT administration to guinea pigs in vivo also selectively inhibited adrenal xenobiotic metabolism. At single doses of 25 or 50 mg/kg, ABT effected rapid decreases in spectrally detectable adrenal P450 concentrations. The higher dose caused approx. 75% decreases in microsomal and mitochondrial P450 levels within 2 h. The decreases in P450 were sustained for 24 h but concentrations returned to control levels within 72 h. Accompanying the ABT-induced decreases in adrenal P450 content were proportionately similar decreases in P450-mediated xenobiotic and steroid metabolism. Microsomal benzo(a)pyrene hydroxylase, benzphetamine N-demethylase, 17-hydroxylase and 21-hydroxylase activities were decreased to 20–25% of control values by the higher dose of ABT. Mitochondrial 11β-hydroxylase and cholesterol sidechain cleavage activities were similarly diminished by ABT treatment. Adrenal 3β-hydroxysteroid dehydrogenase activity, by contrast, was not affected by ABT, indicating specificity for P450-catalyzed reactions. The results demonstrate that ABT in vivo is a non-selective inhibitor of adrenal steroid- and xenobiotic-metabolizing P450 isozymes. The absence of ABT effects on steroid metabolism in vitro suggests that an extra-adrenal metabolite may mediate the in vivo inhibition of steroidogenesis.     

Receptor binding affinity and biological activity of C-terminal elongated forms of endothelin-1

Endothelin-1 (21 amino acids; ET-21) is considered to be derived from a precursor, proendothelin (38 amino acids; ET-38). In order to make the physiological significance of this conversion clear, we synthesized various C-terminal elongated derivatives of ET-21, such as ET-22, ET-23, ET-25, ET-31, ET-36 and ET-38 (each number implies the number of amino acid residues), and measured their receptor binding affinities and biological activities. When inhibition of [¹²⁵I]ET-21 binding to cultured rat smooth muscle cells (A10 cells) was measured, ET-21 inhibited with the highest affinity (IC₅₀ = 1.6 × 10⁻¹⁰ M) and the affinity of ET-38 was 30-fold less than that of ET-21. The binding affinities of the C-terminal elongated peptides were reduced with increasing number of amino acid residues, except for ET-22 whose affinity was lower than those of other peptides (IC₅₀ = 1.6 × 10⁻⁸ M). When contractions of rat aortic segments induced by these peptides were measured, ET-21 was the most potent (EC₅₀ = 2.8 × 10⁻¹⁰ M). All C-terminal elongated peptides, including ET-38, were more than 100-fold less active. It is noteworthy that ET-22 was the least potent peptide (EC₅₀ = 1.2 × 10⁻⁷ M). When bolus doses of C-terminal elongated peptides were administered to chemically denervated rats, the time-dependent change in blood pressure induced by each peptide was different from that induced by ET-21. Although ET-21 elicited a three phase depressor/pressor blood pressure response (an initial rapid hypotension, then a rapid transient hypertension followed by a slowly developing long-lasting hypertensive effect), the C-terminal elongated peptides, including ET-38, did not cause the initial transient hypotensive response. Very interestingly, the ability of the peptides to induce the rapid phase of hypertension in vivo does not seem to be correlated with the affinity of each peptide for the smooth muscle cell receptor, since the peptides with lower affinities for the smooth muscle receptor, such as ET-22, ET-23 and ET-25, showed more potent hypertensive effects. On the other hand, the slow and long-lasting hypertensive effect is likely to be related to the affinity of the compounds. The maximal hypertensive effects of cumulatively administered ET-21 derivatives were similar to those of ET-21. These results suggest that ET-21 is the most potent vasoconstrictor among the peptides and that the conversion from ET-38 to ET-21 may be important as an activation process.     

Bronchopulmonary and pressor effects of big-endothelin-1 in the guinea-pig

Injection of 1 nmol/kg Big-endothelin-1 (ET-1) into anaesthetized and ventilated guinea-pigs did not evoke significant changes in pulmonary inflation pressure and mean arterial blood pressure. In contrast, injection of 1 nmol/kg ET-1 induced marked and rapid bronchoconstrictor and pressor responses. When administered at a dose of 10 nmol/kg, Big-ET-1 induced marked long-lasting changes in pulmonary inflation pressure and mean arterial blood pressure developing slowly as compared to those evoked by ET-1. Furthermore, these increases reached maximal values by 20 min for pulmonary inflation pressure and 45 min for mean arterial blood pressure after injection of the peptide. When Big-ET-1 was incubated with -chymotrypsin [45 min at 37°C, enzyme : substrate ratio (wt/wt) : 0.5%] and injected into guinea-pigs at a dose of 1 nmol/kg, marked bronchoconstrictor and pressor responses were observed, developing with the same kinetics as those evoked by ET-1. The extent of the pressor response was similar and the bronchoconstriction was slightly lower than those evoked upon injection of 1 nmol/kg ET-1 treated or not with -chymotrypsin. The present results indicate that Big-ET exhibits moderate, if any, direct bronchoconstrictor and pressor activities in the guinea-pig. The slow metabolism of Big-ET-1 in an active form probably explains its long-lasting effects at a dose of 10 nmol/kg. This is indirectly confirmed by the in vitro treatment of Big-ET-1 with -chymotrypsin which converts the peptide into an active form.     

Immunocytochemical localization of angiotensin-(1–7) in the rat forebrain

Recent findings by this group have led us to reconsider the view that amino (N−) terminal fragments of angiotensin (Ang) II are inactive degradation products of renin-angiotensin system. To further examine this possibility, an antibody to Ang-(1–7), the N-terminal heptapeptide, was produced to demonstrate the neuroanatomical distribution of the rat brain. Ang-(1–7)-immunoreactivity was found in paraventricular, supraoptic, and suprachiasmatic nuclei, bed nucleus of the stria terminalis, substantia innominata, median eminence, and neurohypophysis. This distribution of Ang-(1–7) in the rat forebrain, together with our previous demonstrations of vasopressin secretion in response to this peptide, suggest that Ang-(1–7) functions as a neuromodulator.     

A library of linear undecapeptides with bactericidal activity against phytopathogenic bacteria

A 125-member library of synthetic linear undecapeptides was prepared based on a previously described peptide H-K¹KLFKKILKF¹⁰L-NH₂ (BP76) that inhibited in vitro growth of the plant pathogenic bacteria Erwinia amylovora, Xanthomonas axonopodis pv. vesicatoria, and Pseudomonas syringae pv. syringae at low micromolar concentrations. Peptides were designed using a combinatorial chemistry approach by incorporating amino acids possessing various degrees of hydrophobicity and hydrophilicity at positions 1 and 10 and by varying the N-terminus. Library screening for in vitro growth inhibition identified 27, 40 and 113 sequences with MIC values below 7.5 μM against E. amylovora, P. syringae and X. axonopodis, respectively. Cytotoxicity, bactericidal activity and stability towards protease degradation of the most active peptides were also determined. Seven peptides with a good balance between antibacterial and hemolytic activities were identified. Several analogues displayed a bactericidal effect and low susceptibility to protease degradation. The most promising peptides were tested in vivo by evaluating their preventive effect of inhibition of E. amylovora infection in detached apple and pear flowers. The peptide H-KKLFKKILKYL-NH₂ (BP100) showed efficacies in flowers of 63–76% at 100 μM, being more potent than BP76 and only less effective than streptomycin, currently used for fire blight control.     

Large and prolonged in vivo response of pancreatic secretion to phenylethylamide and phenylethylester derivatives of Boc-[Nle-Nle]CCK(26–33) in the rat

Supramaximal doses of cholecystokinin (CCK) induce in vitro submaximal biological responses (i.e., smaller by 50% than the response to a maximal dose of CCK), desensitization and residual stimulation, and in vivo secretory inhibition and edematous pancreatitis. It has been reported previously that supramaximal doses of Boc-[Nle²⁸-Nle³¹]CCK(27–32)/-phenylethylester (JMV180) do not produce these effects. The aim of this study was to analyze the in vivo response of pancreatic secretion of the rat to a wide dose range of Boc-[Nle²⁸-Nle³¹]CCK(26–33) (JMV118), an analog of CCK8 with the same activity spectrum as CCK8, to JMV180 and to Boc-[Nle²⁸-Nle³¹]CCK(27–32)-phenylethylamide (JMV170). The three peptides were administered as intravenous infusions and as bolus intravenous injections. In the case of infusions, the same maximal effect was observed with all three peptides. It was obtained with 22.5 pmol/kg · min of JMV118; JMV180 and JMV170 were about 700 times less potent. In the case of bolus injections, the maximal response to JMV118 was observed with 450 pmol/kg, and the response peaked 10–15 min after the injection. Higher doses of JMV118 induced a secretory peak that was smaller and delayed relative to the moment of injection. JMV180 and JMV170 were about 500 times less potent: the maximal response was observed with 218700 pmol/kg and peaked 10–15 min after the injection. Larger doses of JMV180 and JMV170 produced neither supramaximal inhibition nor a delayed peak response, but induced a sustained stimulation of pancreatic secretion that could last more than 3 h after the injection. These data indicate that single large doses of JMV180 and JMV170 can produce a large and long-lasting stimulation of pancreatic secretion in vivo, a goal that cannot be reached with JMV118 or CCK8.     

ACTH(1–24) stimulates the migration of human monocytes in vitro

In view of the increasing evidence that a variety of stresses can influence immune responses, the direct effect of adrenocorticotropic hormone on the migration of human monocytes was studied in vitro. ACTH(1–24) significantly increased the number of migrating cells when placed in the same or the opposite compartment of the chemotaxis chamber, maximum activity being obtained at 10⁻¹⁴ and 10⁻⁸ M. The results indicate that ACTH(1–24) directly and potently stimulates the migration of human monocytes by means of a chemokinetic effect.     

Vascular effects, formation, clearance and release of endothelin peptides in the pig

The formation, release, clearance and vascular effects of endothelin (ET)-like immunoreactivity (-LI) was studied in the pig in vivo. Intravenous infusion of ET-1, 2 and 3 (20 pmol/kg/min for 20 min) increased vascular resistance in the kidney, spleen and skeletal muscle. The most pronounced effects were evoked by ET-1 which caused increases in renal, splenic and skeletal muscle vascular resistance of 554, 528 and 38%, respectively, and a threshold response was observed at 80 pmol/l ET-LI in arterial plasma. During the infusion a large portion of arterial plasma, ET-LI was cleared over the kidney, spleen and skeletal muscle, whereby the most pronounced clearance was observed for ET-1 (73–93%). The ET-1 precursor Big-ET (1–39) given in a similar dose produced only a slight increase in renal vascular resistance (by 20%) and was cleared only over the kidney and not over the spleen or skeletal muscle. Using an ET-1 specific antiserum it was found that plasma ET-1 levels increased 11-fold during the infusion of Big-ET, indicating formation of ET-1 from Big-ET. The half-lives of circulating ET-1, 2 and 3 were 1.3–2.1 min and of Big-ET 8.9 min. Induction of asphyxia for 2 min increased the overflow of ET-LI from the spleen, suggesting local release, and caused splenic vasoconstriction. During i.v. administration of endotoxin for 4 h, arterial plasma ET-LI increased 7-fold and renal and splenic vasoconstrictor responses developed that correlated significantly with the arterial plasma ET-LI. Furthermore, a local release of ET-LI in the spleen was observed during endotoxin administration. Chromatographic characterization of the ET-LI in plasma during endotoxin administration revealed presence of ET-1 and Big-ET. It is concluded that there exists specificity both concerning the vasoconstrictor effects and removal from the circulation of ET peptides, both mechanisms being most prominent for ET-1 in the kidney. Furthermore ET-1 seems to be formed from circulating Big-ET and release of ET-LI can be detected during situations like asphyxia and sepsis.     

Distinct modulation of the endothelin-1 pathway in iNOS-/- and eNOS-/- mice

We hypothesized that constitutive endothelial NO synthase (eNOS) and inducible NO synthase (iNOS) have opposite effects on the regulation of endothelin and its receptors. We therefore sought to determine whether deletions of iNOS or eNOS genes in mice modulate pressor responses to endothelin and the expression of ETA and ETB receptors in a similar fashion. Despite unchanged baseline hemodynamic parameters, anesthetized iNOS-/- mice displayed reduced pressor responses to endothelin-1, but not to that of IRL-1620, a selective ETB agonist. Protein content of cardiac ETA receptors was reduced in iNOS-/- mice compared with wild-type mice, but that of ETB receptors was unchanged. Anesthetized eNOS-/- mice presented a hypertensive state, accompanied by an enhanced pressor response to intravenous endothelin-1, whereas the pressor response to IRL-1620 was reduced. Protein levels were also found to be increased for ETA receptors, but reduced for ETB receptors, in cardiac tissues of eNOS-/- mice. In conscious animals, both strains responded equally to the hypotensive effect of an ETA antagonist, ABT-627, whereas orally administered A-192621, an ETB antagonist, increased MAP to a greater extent in eNOS-/- than in wild-type mice. Furthermore, significant levels of immunoreactive endothelin were found in mesenteric arteries in eNOS-/- but not in iNOS-/- or wild-type congeners. Our study shows that repression of iNOS or eNOS has differential effects on endothelin-1 and its receptors. We have also shown that the heart is the main organ in which iNOS or eNOS repression induces important alterations in protein content of endothelin receptors in adult mice.