Vascular studies with histamine in vitro.

In vitro studies to analyse the pharmacology of histamine-induced dilatation of resistance vessels in rat hindquarters have been made. Histamine caused dose-dependent dilatation of resistance vessels over the concentration range 10(-9) to 10)-6) mol. Responses to histamine were antagonized by cimetidine but not my mepyramine. Dimaprit also caused vasodilatation. Responses to dimaprit were inhibited by cimetidine 10(-6) to 10(-5) M. A pA2 of 6.43 (6.11 - 6.75, 95% confidence limits) was calculated for cimetidine in the resistance vessels of the hindquarters.