Hemodynamic actions of diuretic agents.

The blood pressure lowering effect of diuretics in hypertensive disease is well documented. The hemodynamic actions underlying this antihypertensive effect differ in the early phase from the effects observed during long-term treatment. This article first describes new experiments on the hemodynamic effects of three diuretics, viz. hydrochlorothiazide, chlorthalidon and furosemide in conscious, chronically instrumented spontaneously hypertensive rats. This animal model was chosen in view of its good applicability for the study of the hemodynamics of antihypertensive drug action. Results show a marked early fall in stroke volume and cardiac index with all three diuretics. Mean arterial blood pressure was decreased only after a delay of several hours, because of an early large increase in total peripheral resistance. This article furthermore discusses possible mechanisms involved in the long-term return of peripheral resistance close to or below pre-treatment values. On the basis of data in the literature it is concluded that adaptation of baroreceptor reflexes, auto-regulatory responses of the peripheral vascular resistance and enhanced production of endogeneous vasodilator substances play an increasingly important role during the long-term hemodynamic actions of diuretic agents.