Significant relationship between renin suppression and atrial natriuretic peptide (alpha-hANP) during volume loading...

We have studied eight men with moderate hypertension to determine the atrial natriuretic peptide (alpha-hANP) response to acute volume expansion. Rapid infusion of 1,000 ml 0.9% saline (10-20 min) caused an increase in central venous pressure (4.7 +/- 1.6 cmH2O) while blood pressure and pulse pressure (arterial baroreceptor load) did not change. Stroke volume and heart rate were not affected by the volume load but plasma renin activity (PRA) was significantly suppressed (from 0.83 +/- 0.14 to 0.68 +/- 0.34 microgram AI I/ml-h; p less than 0.01). A significant hemodilution was also observed. Renal sodium excretion was significantly increased. Arterial alpha-hANP increased significantly from 21.1 +/- 6.1 to 30.5 +/- 4.0 pmol/l (p less than 0.02) during volume expansion. There was a significant correlation between corrected plasma volume increase (urine volume subtracted from the infused volume) and alpha-hANP plasma elevation (r = 0.78; p less than 0.05). There was also a significant negative correlation between changes alpha-hANP and PRA (r = -0.78, p less than 0.05). We conclude that only moderate volume loading in human hypertensives is a mechanism for increase in plasma alpha-hANP levels. The significant negative correlation between changes in alpha-hANP and PRA suggests that alpha-hANP may be the humoral factor at least partly responsible for suppression of renin in hypertensive man. Since increased fluid volume also affects sympathetic renal efferents as well as vasopressin secretion, our observed relationship between volume load and renin may well be related also to such mechanisms.