On a normal diet, hydralazine hydrochloride (20 mg) given intravenously
caused significant increase in plasma
renin activity in five of seven normotensive subjects and ten of 20 patients
with essential hypertension. Seven patients with renovascular hypertension
responded to hydralazine with much
greater increase; the overlap in predrug renin activity between patients
with essential and renovascular hypertension diminished after hydralazine.
Three-day sodium restriction enhanced
the effect of hydralazine in a majority
of patients with essential hypertension;
the postdrug renin activity exceeded
8 mμg/ml in 11 of the 12 patients.
In all four patients with primary
aldosteronism renin activity remained
undetectably low even after hydralazine
combined with sodium restriction. The
findings suggest that the hydralazine
test might be useful in the differential
diagnosis of hypertension. However, the
drug should be used carefully because
of untoward side effects.