Hemodynamic and vascular responses to antihypertensive treatment with adrenergic blocking agents: a review.

P atients with established, uncomplicated arterial hypertension are characterized by a normal resting cardiac output and an increased systemic vascular resistance affecting the renal vascular bed most prominently.l-3 The elevated blood pressure can, generally speaking, be lowered by reducing the cardiac output, fower-ing the systemic vascular resistance, or through a combination of both. An ideal antihypertensive agent should lower the blood pressure by reducing both the sys-temic and particularly the renal vascular resistance both at rest and during stress situations of various kinds. As this field is reviewed it becomes apparent that the available information on antihypertensive drugs is based mainly on acute animal experiments and parenteral administration to human subjects. Our knowledge on possible changes induced by long-term treatment is poor. This discussion , therefore, considers three widely used hypotensive agents with adrenergic blocking properties-Rauwolfia preparations, guanethidine, and methyldopa-and separately deals with: (1) acute effects, (2) effects of short-term treatment (less than 4 weeks), and (3) effects of long-term treatment. Rauwolfia preparations AC& e$ects. Only two studies of the acute effects on cardiac hemodynamics are available.4,5 In one of them, the effect of 2.5 mg. of reserpine given intramuscularly was observed 4 hours after administration.4 The blood pressure dropped in all cases. In patients with borderline hypertension and elevated cardiac output, the cardiac output decreased, while in those with normal cardiac output but elevated systemic vascular resistance, the latter decreased. The heart rate did not change. During head-up tilting, five of eleven reserpine-treated patients fainted, indicating an orthostatic action which is not generally seen with this agent. In the other study on only four subjects, both cardiac output and systemic resistance fell after intravenous administration of 1.0 to 5.0 mg.5 After intravenous administration of reser-pine, a slight reduction in glomerular filtration rate was noted, and the excretion of water and electrolytes decreased.6 Parenteral reserpine increased digital blood flow significantly in both normoten-sive and hypertensive subjects.' The mean blood pressure and systemic resistance fell without consistent changes in heart rate.