Histamine H1- and H2-receptors in canine renal artery in vivo and in vitro.

The present work investigates (a) the modification by pretreatment with selective H1- and H2-receptor antagonists on the dose-response curves (DRC) to histamine for heart rate, blood pressure, renal arterial blood flow and renal vascular resistance in anesthetized dogs, and (b) the characteristics of the DRC to histamine in canine isolated renal artery. In vivo, pretreatment with metiamide (10 mg/kg i.v.) did not modify the DRC to histamine. In contrast, significant rightward shift of the DRC to histamine for all the hemodynamic parameters was observed after diphenhydramine (5 mg/kg i.v.). Combined pretreatment with metiamide and diphenhydramine resulted in further rightward displacement of the DRC to histamine. Analysis of the DRC to the relaxant effect of histamine in depolarized (K+ 67 mM) isolated canine renal artery yielded an ED50 of 3.3 x 10(-4) M and a Hill coefficient of 1.74. The results demonstrate the existence of the two types of histamine receptors, H1 and H2, in the renal artery of the dog, both mediating dilator responses, although the H1-receptor appears to predominate.