Enkephalin inhibition of angiotensin-stimulated release of oxytocin and vasopressin.
The effect of leucine5 -enkephalin on angiotensin II (AII)-stimulated release of oxytocin and vasopressin (VP) was investigated in the conscious male rat. Changes in the plasma concentration ([]) of both oxytocin and VP were measured in animals: (1) 60 s after intracerebroventricular (i.v.t.) administration of either artificial cerebrospinal fluid (CSF) or CSF with AII (10, 50, 100 ng/5 microliter); (2) 30, 60, 90 and 300 s after single injection of AII (50 ng/5 microliter; i.v.t.) or CSF and (3) 60 s after AII (50 ng/5 microliter) or CSF in animals pretreated with leucine5 -enkephalin (100 ng/5 microliter; i.v.t.) or CSF (5 microliter). Oxytocin and VP were quantified by radioimmunoassay and values corrected for 100% recovery. The development of a sensitive radioimmunoassay for oxytocin is described. The antiserum for oxytocin enabled detection of greater than or equal to 0.8 pg/ml oxytocin with cross-reactivity of 0.01% with arginine vasopressin and 0.10% with arginine vasotocin. The inter- and intra-assay coefficients of variation were 3-9% and 3.2%, respectively. The hypotheses being tested were that i.v.t. injection of AII stimulates release of both neurohypophysial hormones non-selectively and that leucine5 -enkephalin inhibits both AII-stimulated oxytocin and VP release. Angiotensin II at doses ranging from 10 to 100 ng/5 microliter, i.v.t. increased the plasma concentration of both oxytocin and VP. Plasma levels of both neurohypophysial hormones were elevated 30 s after AII administration i.v.t. and remained elevated 300 sec later.(ABSTRACT TRUNCATED AT 250 WORDS)
D000804:Angiotensin II / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D000818:Animals; D001127:Arginine Vasopressin / Q000097:blood*; D001921:Brain / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004743:Enkephalin, Leucine / Q000494:pharmacology*; D005260:Female; D007276:Injections, Intraventricular; D007774:Lactation / Q000187:drug effects; D008297:Male; D010121:Oxytocin / Q000097:blood*; D011247:Pregnancy; D051381:Rats; D011919:Rats, Inbred Strains; D014882:Water-Electrolyte Balance / Q000187:drug effects
D000804:Angiotensin II; D001127:Arginine Vasopressin; D010121:Oxytocin; D004743:Enkephalin, Leucine; C014622:angiotensin II, Ile(8)-