Characterization of histamine receptors in the ureter of the dog

Abstract

We investigated the effects of histamine on the motility of isolated segments from canine ureters and characterized pharmacologically the histamine receptors involved. We also evaluated the effects of various autacoids (5-HT, carbachol, noradrenaline, thromboxane, prostaglandin F 2α) on the motility of canine ureters. Histamine as well as the H 1 receptor agonist 2-(2-pyridyl)ethylamine elicited a concentration-dependent contraction. This contractile response was antagonized by dimethindene, causing a rightward shift (pA 2 8.30) and a reduction of the slope and the maximal effect (pD′ 2 6.01) of the concentration-response curve. The histamine H 2 receptor antagonist cimetidine in a concentration of 10 −5 mol/l was ineffective concerning the concentration-response curve for histamine. After precontraction of the ureter segments (5-HT, carbachol, prostaglandin F 2α), a concentration-dependent relaxant effect was evaluated in the presence of histamine or the histamine H 2 receptor agonist impromidine. The histamine H 2 receptor antagonist cimetidine attenuated the relaxant response, causing a rightward shift of the concentration-response curve. All autacoids except thromboxane were capable of increasing contractility in canine ureters. Comparing the absolute contractile force in the presence of prostaglandin F 2α. 5-HT, carbachol, noradrenaline and potassium, we found that histamine exhibits the most marked effect on this parameter in the canine ureter. It is concluded that there are two types of histamine receptors modulating contractile activity in the canine ureter: histamine H 1 receptors, which mediate contraction, and histamine H 2 receptors, which mediate relaxation (in the precontracted tissue).