Peripheral effects of guanfacine compared to those of clonidine in the dog.

Comparative studies of the antihypertensive agents, guanfacine and clonidine, on their peripheral effects were performed using normotensive canine preparations. On the peripheral vascular beds, both drugs constricted cerebral renal and femoral vasculatures, but there were no decreases in the renal blood flow. This vasoconstriction was blocked by phentolamine, and guanfacine was about 3 times less potent than clonidine. Both drugs contracted the canine nictitating membrane, and had no effect on the ganglionic transmission in the cervical sympathetic ganglion. Qualitatively different effects were observed in their effects on renal function. Guanfacine slightly increased the urinary volume and Na excretion, while clonidine increased the urinary volume and K excretion. All these peripheral effects do not seem to be responsible for their hypotensive effect.