title: Mechanism of alpha 2-adrenoceptor agonist-induced diuresis.
abstract: In vivo and in vitro studies were performed to assess the mechanism of the diuretic effect of B-HT 933, a selective alpha 2-adrenoceptor agonist. In conscious Sprague-Dawley rats whose plasma vasopressin (AVP) levels were increased by infusion of hypertonic NaCl, B-HT 933 had no effect on AVP secretion. In Brattleboro homozygous (DI) rats, the antidiuretic dose response to AVP was shifted to the right by B-HT 933. In addition, a sustained antidiuresis induced in rats by infusion of 10 pg/min AVP was attenuated by B-HT 933 in a concentration-dependent manner. Pretreatment of DI rats with pertussis toxin (2 micrograms/kg iv) 4-5 days before testing abolished the inhibitory effect of B-HT 933 on AVP-induced antidiuresis. In outer medullary collecting ducts of DI rats, norepinephrine and B-HT 933 produced significant inhibition of AVP-stimulated adenosine 3',5'-cyclic monophosphate (cAMP) accumulation. In contrast, the selective alpha 1-adrenoceptor agonist cirazoline had no effect on AVP-induced cAMP formation. The inhibitory effect of norepinephrine was antagonized by the selective alpha 2-adrenoceptor antagonist rauwolscine but not by prazosin, a selective alpha 1-antagonist. In outer medullary collecting ducts dissected from the pertussis toxin-treated DI rats used in the in vivo studies, the inhibitory effect of norepinephrine and B-HT 933 on AVP-stimulated cAMP accumulation was abolished. The results indicate that the hydrosmotic action of AVP is inhibited by alpha 2-agonists via a pertussis toxin-sensitive mechanism.
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D001127:Arginine Vasopressin / Q000008:administration & dosage / Q000494:pharmacology; D001381:Azepines / Q000008:administration & dosage / Q000494:pharmacology*; D000242:Cyclic AMP / Q000378:metabolism; D004231:Diuresis / Q000187:drug effects*; D007262:Infusions, Intravenous; D007684:Kidney Tubules / Q000187:drug effects / Q000502:physiology*; D007685:Kidney Tubules, Collecting / Q000187:drug effects / Q000502:physiology*; D008297:Male; D051381:Rats; D011910:Rats, Brattleboro; D011919:Rats, Inbred Strains; D012016:Reference Values; D013045:Species Specificity
chemical_list: D000316:Adrenergic alpha-Agonists; D001381:Azepines; D001127:Arginine Vasopressin; C015603:azepexole; D000242:Cyclic AMP