Effect of propranolol and labetalol on renal haemodynamics at rest and during exercise in essential hypertension.

The effect of exercise on renal haemodynamics was studied in young patients with mild essential hypertension. Four groups of subjects were studied: thirteen normotensive, healthy control subjects, fifteen untreated, eleven propranolol-treated, and six labetalol-treated patients. Renal plasma flow (RPF) and glomerular filtration rate (GFR) were measured during four consecutive periods, a pre-exercise control period, two exercise periods with loads of 450 kpm/min and 600 kpm/min, respectively, and a postexercise control period. In the untreated patients RPF and GFR were lower during exercise than in the normotensive control subjects, whereas no significant differences were found at rest. In the propranolol-treated patients the reduction in RPF and GFR during exercise were more pronounced than in the untreated hypertensives. In the labetalol-treated patients however, RPF and GFR were reduced only to the same degree as in the untreated hypertensive patients. The reduced renal blood flow in propranolol-treated patients could be attributed to a compensatory increased sympathetic activity caused by an impaired cardiac response to exercise. The lack of reduction in renal blood flow during labetalol therapy could partly be related to alpha-adrenoceptor blockade in the renal vascular bed induced by labetalol, and partly to a lesser degree of reduction in cardiac output during labetalol than propranolol therapy.