Contrasting renal haemodynamic responses to the angiotensin converting enzyme inhibitor enalapril and the beta-adrenergic antagonist metoprolol in essential hypertension.
The individual target organ response to blood pressure reduction is an important criterion in the selection of appropriate antihypertensive therapy. We assessed both the renal and the systemic haemodynamic responses to antihypertensive monotherapy (five to seven weeks) with the angiotensin converting enzyme (ACE) inhibitor enalapril (n = 12), in contrast to the cardioselective beta-adrenergic blocker metoprolol (n = 11) in subjects with essential hypertension. Enalapril lowered systolic and diastolic blood pressure, and the fall in blood pressure was mediated haemodynamically by a 34% fall in systemic vascular resistance. In the kidney, glomerular filtration rate, renal plasma flow and renal blood flow were maintained by a 23% fall in renal vascular resistance. The disproportionate fall in systemic resistance versus renal resistance actually reduced the renal fraction of cardiac output. By contrast, metoprolol lowered predominantly diastolic blood pressure, with an associated 25% fall in cardiac output, without significant changes in overall systemic vascular resistance. In the renal circulation, renal perfusion was well maintained by a 20% fall in renal vascular resistance, perhaps at the efferent arteriole, without change in the renal fraction of cardiac output. Neither drug altered weight, plasma volume or total blood volume. Thus, each drug represents effective antihypertensive monotherapy, with a generally favourable, though different, renal haemodynamic profile, characterized by effective autoregulation of renal perfusion even in the face of a fall in perfusion pressure.