Sams, W. Mitchell

Vasodilating agents were tested on smooth-muscle strips of small arterial blood vessels of dog and rabbit skin and mesentery, and two patterns of reaction were demonstrated. The type 1 Vasodilating agents, for example nicotinate, caused relaxation of contracted strips or blocked their contraction. The type 2 Vasodilating compounds, histamine, choline esters, and bradykinin, either caused contraction or had no effect on the vascular smooth-muscle preparation. Responses that were species specific and region specific characterize the action of type 2 vasodilators and must be accounted for in any in-vitro testing procedure for vasodilator drugs.