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

ABSTRACT

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. The blood pressure effect of urapidil and prazosin resembled more the pattern seen with typical venous dilators (molsidomine and nitrates) and was not accompanied by significant increases in heart rate and in PRA. Hence, the magnitude of diastolic blood pressure reduction seems to be an essential determinant of reflex counterregulation. The results prove that some few parameters can give information about the overall pattern of hemodynamic effects of vasodilators.