Characterization of vasodilators by comparison of their effects on blood pressure, counterregulation and myocardial oxygen demand in conscious normotensive dogs.

Vasodilators were characterized on the basis of their first-dose effect on systolic and diastolic blood pressure, heart rate, on the product of heart rate and systolic blood pressure and on plasma renin activity (PRA) in conscious normotensive dogs. The compounds were given orally to the animals and the effects were studied over a period of 4 h. The arterial vasodilators (propyldazine, dihydralazine and labetalol) caused a marked reduction of systolic and diastolic blood pressure with excessive stimulation of the sympathetic nervous system, leading to an increase in myocardial oxygen demand.