Intrinsic sympathomimetic activity of cardioselective beta-adrenoceptor blockers and effects on renal function

The effects of a 21 infusion of isotonic sodium chloride on renal haemodynamics and sodium excretion were measured in nine normotensive volunteers. Changes in these responses to volume expansion induced by cardioselective beta-adrenoceptor blockade by drugs with (epanolol) and without intrinsic sympathomimetic activity (atenolol) were examined. Renal plasma flow was significantly lower before, during and after sodium chloride infusion whilst on treatment with atenolol compared with epanolol. Urinary sodium excretion was lower on atenolol than epanolol. Glomerular filtration rate was unchanged by either drug. Basal urinary kallikrein excretion was diminished by atenolol and both epanolol and atenolol inhibited the rise in urinary kallikrein excretion after sodium chloride infusion. Although some of these findings may be due to a more potent hypotensive effect of atenolol, intrinsic sympathomimetic activity may contribute to the apparent protective effects of epanolol on renal function.