Effect of sodium loading and exercise on renal haemodynamics and urinary sodium excretion in young patients with essential hypertension before and during propranolol treatment.

The effects on renal plasma flow (RPF) and glomerular filtration rate (GFR) of an i.v. sodium load and exercise have been measured in 14 young patients with essential hypertension before and after 3-4 months' treatment with propranolol as well as in 10 normotensive control subjects. In the untreated hypertensive patients, RPF and GFR were significantly reduced during sodium loading and exercise. After propranolol treatment, RPF and GFR were unaffected by sodium loading but decreased during exercise. In the normotensive control group, GFR and RPF were unchanged during sodium loading; RPF decreased during exercise, wherease GFR was not significantly reduced. RPF was significantly lower in the untreated hypertensive patients than in the normotensive control subjects during sodium loading and exercise. Propranolol treatment induced a significant reduction of BP and heart rate. RPF and GFR were not altered by propranolol treatment during sodium loading. During exercise, however, RPF was significantly lower after treatment than before. Urinary sodium excretion during sodium loading was significantly higher in the hypertensive patients than in the control subjects and decreased significantly during propranolol treatment. The reason for the abnormal reduction in renal haemodynamics during sodium loading in patients with essential hypertension is not clarified, but may possibly be related to functional or structural alterations in the renal vascular bed. The lower RPF during exercise after treatment with propranolol is most likely caused by an inhibition of the cardiac output induced by beta-adrenergic blockade. It is conceivable that the reduced urinary sodium excretion during propranolol treatment is attributable to the reduction of BP.