title: Inhibition of vasopressin-stimulated cyclic AMP accumulation by alpha-2 adrenoceptor agonists in isolated papillary collecting ducts.
abstract: The effects of selective alpha adrenoceptor agonists and antagonists on vasopressin (VP)-sensitive cyclic AMP (cAMP) formation in microdissected rat papillary collecting ducts were examined. In the presence of 10(-10) M VP, norepinephrine and the selective alpha-2 adrenoceptor agonist, B-HT 933, produced almost total inhibition of VP-stimulated cAMP accumulation. Half-maximal inhibition occurred at 1 x 10(-8) M and 6 x 10(-7) M for norepinephrine and B-HT 933, respectively. Cirazoline, a selective alpha-1 adrenoceptor agonist, had no significant effect on VP-stimulated cAMP accumulation. The inhibitory effects of norepinephrine and B-HT 933 were antagonized by rauwolscine but not by prazosin. The antagonism of B-HT 933-induced inhibition of VP-stimulated cAMP accumulation was competitive with an antagonist dissociation constant (KB) of 10.9 x 10(-9) M. Preincubation of papillary collecting ducts with pertussis toxin (1 microgram/ml for 1 hr at 37 degrees C) attenuated, by 65%, the inhibitory effect of B-HT 933 on VP-stimulated cAMP levels. These results demonstrate that alpha-2 adrenoceptors capable of inhibiting VP action are present on the papillary collecting duct. Furthermore, the alpha-2 adrenoceptor-induced inhibition of VP-stimulated cAMP accumulation is pertussis-toxin sensitive. This suggests that alpha-2 adrenoceptors are coupled negatively to adenylate cyclase, via the guanine nucleotide binding protein, in the collecting tubule.
mesh_terms: D037361:Adenylate Cyclase Toxin; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D001381:Azepines / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D007684:Kidney Tubules / Q000187:drug effects*; D007685:Kidney Tubules, Collecting / Q000187:drug effects*; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology; D037342:Pertussis Toxin; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects; D014667:Vasopressins / Q000037:antagonists & inhibitors*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D037361:Adenylate Cyclase Toxin; D000316:Adrenergic alpha-Agonists; D001381:Azepines; D011942:Receptors, Adrenergic, alpha; D010566:Virulence Factors, Bordetella; D014667:Vasopressins; C015603:azepexole; D000242:Cyclic AMP; D037342:Pertussis Toxin; D009638:Norepinephrine