Effect of various states of hydration on plasma ADH and renin in man

To investigate the interaction between antidiuretic hormone (ADH) and renin-angiotensin system, plasma ADH and plasma renin activity (PRA) were determined in normal subjects (n = 10) under various hydrated states. Four experimental conditions, i.e., water loading, infusion of hypertonic saline, acute dehydration induced by furosemide and postural changes, were chosen. 1. Upright posture decreased plasma volume by 9.5 +/- 0.9% without significant changes in plasma osmolality. PRA increased from 5.2 +/- 0.7 to 8.3 +/- 0.8 ng/ml. However, plasma ADH did not change significantly (1.9 +/- 0.3 to 1.8 +/- 0.2 muU/ml). 2. When furosemide was administered intravenously under this condition, both plasma ADH and PRA increased to 3.1 +/- 0.5 muU/ml and 15.5 +/- 1.6 ng/ml with 11.2 +/- 1.1% decrease in plasma volume. Plasma osmolality did not change significantly. 3.Water load resulted in a decrease in plasma osmolality from 282.6 +/- 0.9 to 278.6 +/- 1.2 mOsm/kg without significant change in plasma volume. Significant decrease in plasma ADH level from 2.6 "/- 0.4 to 0.6 "/- 0.1 muU/ml was found, but PRA (7.8 +/- 1.1 ng/ml) did not change (6.3 +/- 1.0 ng/ml). 4. Hypertonic saline infusion brought about an increase in plasma osmolality to 290.1 +/- 0.8 mOsm/kg with simultaneous increase in plasma volume by 6.7 +/- 1.3%. Plasma ADH level also increased to 2.4 +/- 0.3 muU/ml, while PRA decreased to 4.2 +/- 0.3 mg/nl. Accordingly, significant correlation between changes in PRA and plasma ADH level, was not observed. We suggest that plasma osmolality is the dominant variable in regulating plasma ADH level, but in the presence of a sufficient degree of hypovolemia, the osmotic domination was overcome. On the other hand, PRA was strongly influenced by changes in effective blood volume other than changes in plasma osmolality.