Hormonal responses to change in posture in hypertensive man. Evaluation by measurements of prostaglandin E2, renin activity, angiotensin II, and norepinephrine in renal venous blood.

The hormonal responses to the stimulus of changing from resting supine to sitting upright for 15 minutes were assessed in 20 patients with hypertension, divided into 2 groups. 8 patients had essential hypertension (EH) and 12 unilateral renal artery stenosis (URS). The prostaglandin E2 (PGE2) concentration, plasma renin activity (PRA), angiotensin II (A-II) concentration, and norepinephrine (NE) concentration were measured in renal vein blood using specific methods. The PGE2 concentration increased after sitting for 15 minutes in all patients (p less than 0.001), but the increment was significant only in those with URS. The PRA was lower both at rest and after sitting up in the EH group than in the URS group. After sitting up the A-II concentration increased more in patients with URS than in those with EH (p less than 0.05). NE levels rose significantly when all patients were included (p less than 0.01), mainly owing to changes in the EH group. Supine and sitting PRA and A-II were correlated (r=0.47 and r=0.52; both p less than 0.05), and also sitting PGE2 and A-II (r=0.46, p less than 0.05). The inverse relation between PGE2 and NE for the difference in hormone concentrations between supine and sitting (r=-0.44, p less than 0.05) may be explained by an inhibitory effect of PGE2 on renal NE release, earlier observed in experiments in vitro. Similar changes in PGE2 and the measured components of the renin-angiotensin system in response to change in posture may indicate these factors are interrelated.