phosphoramidon and Hypoxia

Previously, we showed that carotid bodies express neutral endopeptidase (NEP)-like enzyme activity and that phosphoramidon, a potent inhibitor of NEP, potentiates the chemosensory response of the carotid body to hypoxia in vivo. NEP has been shown to hydrolyze methionine enkephalin (Met-Enk) and substance P (SP) in neuronal tissues. The purpose of the present study is to determine whether NEP hydrolyzes Met-Enk and SP in the carotid body and if so whether these peptides contribute to phosphoramidon-induced potentiation of the sensory response to hypoxia. Experiments were performed on carotid bodies excised from anesthetized adult cats (n = 72 carotid bodies). The hydrolysis of Met-Enk and SP was analyzed by HPLC. The results showed that both SP and Met-Enk were hydrolyzed by the carotid body, but the rate of Met-Enk hydrolysis was approximately fourfold higher than that of SP. Phosphoramidon (400 microM) markedly inhibited SP hydrolysis ( approximately 90%) but had only a marginal effect on Met-Enk hydrolysis ( approximately 15% inhibition). Hypoxia (PO(2), 68 +/- 6 Torr) as well as exogenous administration of SP (10 and 20 nmol) increased the sensory discharge of the carotid body in vitro. Sensory responses to hypoxia and SP (10 nmol) were potentiated by approximately 80 and approximately 275%, respectively (P < 0.01), in the presence of phosphoramidon. SP-receptor antagonists Spantide (peptidyl) and CP-96345 (nonpeptidyl) either abolished or markedly attenuated the phosphoramidon-induced potentiation of the sensory response of the carotid body to hypoxia as well as to SP. These results demonstrate that SP is a preferred substrate for NEP in the carotid body and that SP is involved in the potentiation of the hypoxic response of the carotid body by phosphoramidon.

Topics: Animals; Biphenyl Compounds; Carotid Body; Cats; Chromatography, High Pressure Liquid; Dose-Response Relationship, Drug; Enkephalin, Methionine; Female; Glycopeptides; Hydrolysis; Hypoxia; Kinetics; Male; Neprilysin; Neurokinin-1 Receptor Antagonists; Oxygen; Receptors, Neurokinin-1; Substance P

Carotid body expresses neutral endopeptidase (NEP)-like enzyme activity and phosphoramidon, an inhibitor of NEP augments sensory response of the carotid body to hypoxia (Kumar et al., 1990). NEP hydrolyzes substance P (SP) and methionine enkephalin (Met-ENK) in the nervous system. In the present study, we determined whether NEP hydrolyzes Met-ENK and SP in the carotid body and whether these peptides contribute to the phosphoramidon-induced potentiation of the sensory response to hypoxia. Experiments were performed on carotid bodies excised from anaesthetized adult cats. HPLC analysis showed that both SP and Met-ENK were hydrolyzed by the carotid body. Phosphoramidon (400 microM) markedly inhibited SP (approximately 90%) but had only marginal effect on Met-ENK hydrolysis (approximately 15%). Sensory responses of the carotid body in vitro to hypoxia (pO2, 68 +/- 6 mmHg) and SP (10 nmoles) were potentiated by phosphoramidon by approximately 80% and approximately 275% respectively (p < 0.01). SP-receptor antagonist abolished phosphoramidon-induced potentiation of the sensory response to hypoxia as well as to SP. These results demonstrate that SP is a preferred substrate for NEP in the carotid body and SP plays a major role in the potentiation of the hypoxic response of the carotid body by phosphoramidon.

Topics: Animals; Carotid Body; Cats; Enkephalin, Methionine; Female; Glycopeptides; Hydrolysis; Hypoxia; In Vitro Techniques; Male; Neprilysin; Neurokinin-1 Receptor Antagonists; Substance P

The aims of this study were to investigate whether angiotensin II and/or endothelin could contribute to the hypoxic contractile response of isolated rat pulmonary artery. Experiments were performed for 1 h on noradrenaline precontracted arterial rings in hypoxic conditions (95% N2 and 5% CO2). Nicardipine, lisinopril, losartan, phosphoramidon, FR139317 and bosentan were used to block Ca2+ channels, angiotensin I-converting enzyme, AT1 receptors, endothelin-converting enzyme, ETA receptors, and ETA/ETB receptors, respectively. The profile of the hypoxic contractile response was biphasic, displaying, after a short relaxation, a weak and transient contraction (from 2-4 min) and then, before complete relaxation, a slowly developed but sustained contraction (from 14-60 min). Endothelium removal abolished the transient contraction and reduced (-59%) the sustained contraction. Nicardipine did not modify the transient contraction, but concentration-dependently decreased (from -35% to -100%) the sustained contraction (P = 0.024). Lisinopril and losartan did not affect the response (P = 0.418 and P = 0.973, respectively). Bosentan did not modify the transient contraction, but concentration-dependently decreased (from -14% to -71%) the sustained contraction (P = 0.016), whereas phosphoramidon and FR139317 did not affect the response (P = 0.830 and P = 0.806, respectively).. In rat, (i) both phases of the hypoxic contractile response are endothelium-dependent and independent of angiotensin II; (ii) the transient contraction does not depend on endothelin; (iii) the sustained contraction, which involves calcium influx, appears partly dependent on mature endothelin released from storage granules by stimulating ETB receptors.

Topics: Angiotensin I; Angiotensin II; Angiotensin Receptor Antagonists; Angiotensin-Converting Enzyme Inhibitors; Animals; Azepines; Bosentan; Calcium; Calcium Channel Blockers; Endothelin Receptor Antagonists; Endothelins; Endothelium, Vascular; Extracellular Space; Glycopeptides; Hypoxia; In Vitro Techniques; Indoles; Lisinopril; Losartan; Male; Muscle Contraction; Muscle, Smooth, Vascular; Nicardipine; Pulmonary Artery; Rats; Rats, Wistar; Sulfonamides

Acute systemic hypoxia induces mesenteric venoconstriction in intact rabbits in part because of an increase in chemoreflex-mediated sympathetic efferent nerve activity. Inhaled anesthetics attenuate this reflex response. The direct effects of hypoxia on mesenteric veins are unknown. The purpose of the current study was to examine the effects of hypoxia on isolated rabbit mesenteric capacitance veins and to determine the effects of halothane, isoflurane, and enflurane on the responses to hypoxia.. Isometric tension was measured before, during, and after 10 min of hypoxia in the rings of either quiescent or norepinephrine contracted veins, with or without endothelium. Effects of various pharmacologic agents and volatile anesthetics on the responses to hypoxia were examined.. Hypoxia augmented contractions to norepinephrine and phenylephrine only in endothelium-intact veins. The hypoxic response was inhibited by phentolamine (alpha-adrenoceptor antagonist) and abolished in the absence of extracellular Ca2+. There were no effects of propranolol (beta-adrenoceptor antagonist), ryanodine (a sarcoplasmic reticulum Ca2+ depleter), indomethacin (cyclooxygenase inhibitor), or nordihydroguaiaretic acid (lipoxygenase inhibitor). L-NAME (an inhibitor of nitric oxide synthase) enhanced basal sensitivity of veins to norepinephrine but had no effect on the response to hypoxia. Nicardipine (a blocker of voltage-gated calcium channels) depressed the hypoxic contraction by 86 +/- 5%, phosphoramidon (an inhibitor of endothelin-converting enzyme) by 82 +/- 8%, and BQ-123 (a specific endothelin-1 receptor antagonist) by 47 +/- 10%. Volatile anesthetics (1.0 MAC) inhibited responses to hypoxia in the absence as well as presence of L-NAME.. These results suggest that in mesenteric capacitance veins of rabbits an intrinsic vascular mechanism contributes to endothelium-dependent hypoxic augmentation of contraction to alpha-adrenergic agonists that involve activation of endothelin-1, an endothelium-derived constricting factor. Inhibition of hypoxic contraction by volatile anesthetics is not mediated by endothelium relaxing factor.

Topics: Acetylcholine; Animals; Arginine; Endothelium, Vascular; Enflurane; Glycopeptides; Halothane; Hypoxia; In Vitro Techniques; Indomethacin; Isoflurane; Male; Masoprocol; NG-Nitroarginine Methyl Ester; Nicardipine; Norepinephrine; Peptides, Cyclic; Rabbits; Ryanodine; Vasoconstriction

The role of phosphoramidon-sensitive endothelin converting enzyme in the release of endogenous endothelin-1 was investigated in anesthetized rats. Intravenous infusion of phosphoramidon 0.3 mg/kg/min did not suppress the release of endothelin-1 stimulated by hemorrhage or cytokines. Elevation of endothelin-1 in rats subjected to hypoxia was not modified by phosphoramidon (0.1 or 0.3 mg/kg/min for 2 h). A high dose of phosphoramidon (10 mg/kg i.v. +0.1 mg/kg/min) significantly potentiated the hypoxia-induced increases in plasma endothelin-1 levels. Increases in endothelin-1 release caused by bilateral nephrectomy were further enhanced by hypoxia. It is concluded that the release of endogenous endothelin-1 release stimulated by hemorrhage, cytokines and hypoxia is resistant to inhibition by phosphoramidon, and at high doses, phosphoramidon potentiates hemorrhage- and hypoxia-induced increases in endothelin-1 levels, most likely by preventing its degradation.

Topics: Animals; Aspartic Acid Endopeptidases; Blood Pressure; Cytokines; Dose-Response Relationship, Drug; Endothelin-Converting Enzymes; Endothelins; Endotoxins; Glycopeptides; Hemorrhage; Hypoxia; Infusions, Intravenous; Interleukin-1; Male; Metalloendopeptidases; Nephrectomy; Rats; Tumor Necrosis Factor-alpha

1. Chronic hypoxic rats are always polycythaemic. It is possible that an increase in packed cell volume may enhance erythrocyte trapping with a consequent increase in renal damage after renal ischaemia. These experiments were designed to assess renal functional changes after renal arterial occlusion in chronic hypoxic rats. 2. Chronic hypoxic rats were prepared by exposure (15h/day) to an altitude chamber (5486m) for 4 weeks. 3. After 45 min of left renal arterial occlusion, there were significant decreases in the excretion of potassium, p-aminohippurate and inulin and in the p-aminohippurate extraction ratio in 12 sea level ischaemic insulted kidneys. In 12 chronic hypoxic rats, the same parameters were changed after left renal ischaemia but only the p-aminohippurate ratio was significantly altered. 4. Administrations of 1 or 5 mg/kg phosphoramidon did not cause any significant improvement in the measured renal parameters in both kidneys and in both groups of rats after ischaemia. 5. In the second experiment, the rats were challenged by rapid infusion of 10 ml of saline intravenously, and urine was collected for 90 min from each ureter. Four hours after left renal arterial occlusion, the insulted kidney showed increased water and sodium excretion in both sea level and chronic hypoxic rats. However, 24 h after left renal ischaemia, the responses of sea level and chronic hypoxic rats were different. Urinary excretion was significantly reduced in sea level rats, but was almost normal in chronic hypoxic rats. 6. This report suggests that some beneficial factors after chronic hypoxia might play important roles in reducing the damage after renal ischaemia.

Topics: Acute Kidney Injury; Animals; Body Weight; Chronic Disease; Glycopeptides; Hematocrit; Hypoxia; Insulin; Ischemia; Kidney; Male; p-Aminohippuric Acid; Potassium; Rats; Rats, Sprague-Dawley

Endothelin (ET)-1 is a potent vasoactive peptide elaborated by the vascular endothelial cells. In the present study we examined the effects of ischemia-hypoxia (I/H) on ET-1 release from isolated perfused guinea pig lungs and heart. Guinea pig lungs subjected to 15 min I/H followed by reperfusion and reventilation significantly (P less than .05) augmented ET-1 release from 14.1 +/- 2.7 to 30.4 +/- 5.6, 27.3 +/- 4.0 and 28.0 +/- 5.0 pg/g of dry weight of lung at 15, 30 and 45 min after I/H, respectively. Pretreatment of guinea pigs with phosphoramidon (10 mg/kg i.v.), an ET converting enzyme inhibitor, 10 min before the removal of lungs abrogated the I/H-induced increases in ET-1 release without affecting the base-line values of ET-1. Phosphoramidon also attenuated the elevations in pulmonary insufflation pressure (PIP) produced by I/H. Moreover, infusion of big ET-1 (BET-1; 30 micrograms/over 15 min) into isolated perfused guinea pig lungs enhanced PIP that was abolished by phosphoramidon. Isolated guinea pig hearts subjected to 15 or 30 min of global ischemia exhibited no disturbances in ET-1 release or mechanical activity. In addition, the increases in perfusion pressure elicited by BET-1 infusion (12 micrograms/over 30 min) into isolated guinea pig hearts was unaffected by phosphoramidon. In a separate study in anesthetized guinea pigs, phosphoramidon significantly attenuated the increases in blood pressure and PIP elicited by BET-1 (10 micrograms/kg i.v.); the pressor and PIP responses to ET-1 (4 micrograms/kg i.v.) were not affected.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Anti-Bacterial Agents; Blood Pressure; Endothelins; Glycopeptides; Guinea Pigs; Heart; Hypoxia; Ischemia; Lung; Male; Myocardium