title: Effects of naloxone on vasopressin secretion in conscious rats: evidence for inhibitory role of endogenous opioid peptides in vasopressin secretion.
abstract: The effects of naloxone, an opioid antagonist, on arginine vasopressin (AVP) secretion were examined in conscious unrestrained rats under both basal and stimulated conditions. Intravenous injection of naloxone in a dose of 0.1 mg/kg did not significantly affect the basal plasma AVP level. However, 0.5 or 2.5 mg/kg naloxone significantly raised the basal AVP level in euhydrated rats. Naloxone (0.5 mg/kg) significantly enhanced AVP secretion after 72-h water deprivation. However, the enhancement was more prominent in euhydrated rats than in dehydrated rats. Pretreatment with naloxone (0.5 mg/kg) also significantly prolonged AVP secretion induced by intracerebroventricular injection of angiotensin-II (100 ng). Moreover, naloxone (0.5 mg/kg) significantly increased AVP secretion induced by intracerebroventricular injection of carbachol (10 ng). Naloxone (0.5 mg/kg) altered neither basal blood pressure nor the angiotensin-II-induced pressor response, but augmented the carbachol-induced pressor response. This suggests that facilitation of AVP secretion by naloxone is not due to a reflex mechanism resulting from decreased blood pressure. These results indicate that endogenous opioid peptides exert a tonic inhibitory control on AVP secretion in rats.
authors.affiliation: Department of Medicine, Kyoto University School of Medicine, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Yamada
authors.forename: K
authors.initials: K
authors.lastname: Nakao
authors.forename: H
authors.initials: H
authors.lastname: Itoh
authors.forename: G
authors.initials: G
authors.lastname: Shirakami
authors.forename: A
authors.initials: A
authors.lastname: Sugawara
authors.forename: Y
authors.initials: Y
authors.lastname: Saito
authors.forename: M
authors.initials: M
authors.lastname: Mukoyama
authors.forename: H
authors.initials: H
authors.lastname: Arai
authors.forename: K
authors.initials: K
authors.lastname: Hosoda
authors.forename: S
authors.initials: S
authors.lastname: Shiono
mesh_terms: D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002217:Carbachol / Q000494:pharmacology; D003243:Consciousness / Q000502:physiology; D003681:Dehydration / Q000503:physiopathology; D004723:Endorphins / Q000494:pharmacology / Q000502:physiology; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D009292:Narcotic Antagonists; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000187:drug effects / Q000378:metabolism; D014667:Vasopressins / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D004723:Endorphins; D009292:Narcotic Antagonists; D011957:Receptors, Opioid; D014667:Vasopressins; D000804:Angiotensin II; D009270:Naloxone; D002217:Carbachol