Dose-related effects of fenoterol and ritodrine in 10 peripheral vascular beds of the anesthetized dog.

Dose-response curves of the uterine relaxants fenoterol and ritodrine were established for vascular conductance in 10 peripheral arterial beds in anesthetized dogs. Vascular sensitivity was expressed as (E)D50 of conductance response. Fenoterol induced strong vasodilation in all arterial beds except in the kidneys. The gastrointestinal vessels are significantly more sensitive to fenoterol than are muscle and brain vessels. Ritodrine induced strong vasodilation in all arterial beds except in the kidneys and the liver. The vascular sensitivity spectrum of ritodrine differs from that of fenoterol. On a molecular basis fenoterol was 66 times as potent as ritodrine if arterial pressure reduction was used as criterion. When (E)D50 values of vascular conductances of both drugs were plotted against arterial pressure reduction as reference, the gastrointestinal vessels (left gastric, splenic, gastroduodenal, proper hepatic, and superior mesenteric arteries) appeared to be significantly more sensitive to fenoterol than to ritodrine. In contrast, vascular sensitivity in the myocardium, striated muscles, and brain (left coronary, common carotid, femoral, and vertebral arteries) was not statistically different for the two drugs.