[Effects of phenylephrine on atrial natriuretic factor and the renin-aldosterone axis in normal patients and essential hypertensive patients].

Phenylephrine infusions enhance diuresis and natriuresis both in normal subjects and patients with essential hypertension, whereas they have an opposite effect on urinary aldosterone excretion, decreasing it in normal subjects and enhancing it in hypertensive patients. With the new knowledge concerning the atrial natriuretic factor (ANF), it seemed a strong possibility that in normal subjects phenylephrine infusions should exert its effect through the increased release of ANF, as suggested by in vitro studies. Phenylephrine infusions at high pressor dose (to increase diastolic pressure by 25 mmHg) in six healthy volunteers increased plasma ANF and cGMP and decreased plasma renin activity and aldosterone concentrations. Urinary volume, sodium, and cGMP excretion were also increased. Phenylephrine infusions at low pressor dose (to increase diastolic pressure by 12-15 mmHg), in healthy subjects and in five patients with mild essential hypertension, significantly increased plasma ANF concentrations and decreased plasma renin activity to the same degree in both groups. But, whereas in normal subjects plasma aldosterone decreased significantly, it increased in patients with mild essential hypertension despite the simultaneous rise in plasma ANF concentration.