Vasopressin, angiotensin II and renal responses during water immersion in hydrated humans

Abstract

1. The hypothesis was tested that in hydrated humans the release of arginine vasopressin and angiotensin II is suppressed by water immersion (WI) and that this is a mechanism of the immersion-induced diuresis and natriuresis. Seven male subjects on controlled sodium (65-75 mmol per 24 h for 4 days) and water intake were studied. 2. Plasma vasopressin was promptly suppressed by WI, declining from 0. 76 +/- 0.13 to 0.23 +/- 0.08 pg ml-1 (P < 0.05), with a concomitant increase in renal water output (CH2O) from -0.4 +/- 0.2 to 4.4 +/- 0.7 ml min-1 (P < 0.05). Subsequently, CH2O returned to the level of control, whereas plasma vasopressin remained suppressed. Plasma osmolality gradually increased from 285 +/- 1 to 289 +/- 1 mosmol kg-1 (P < 0.05). WI caused a 9-fold increase in renal sodium excretion. Plasma angiotensin II decreased from 27.1 +/- 5.3 to 4.3 +/- 0.7 pg ml-1 (P < 0.05), and the intraindividual correlation coefficients between sodium excretion rates and angiotensin II concentrations varied between 0.73 and 0.96 (P < 0.002). 3. The data demonstrate that plasma vasopressin and angiotensin II concentrations decrease during WI in hydrated humans, concomitantly with initial increases in CH2O and sodium excretion. Therefore, vasopressin could constitute a mediator of CH2O and angiotensin II of the natriuresis of WI. The subsequent return of CH2O to the level of control is, however, also caused by other factors.

Figure 1. Plasma osmolality, plasma vasopressin and solute free water clearance before, during and after 6 h of WI to the neck (○) or during a seated control (•)

Values are means ±s.e.m.; n = 7. †P < 0.05 compared with the mean pre-immersion value; *P < 0.05 compared with the corresponding control value.

Figure 2. Renal sodium excretion and plasma concentration of angiotensin II before, during and after 6 h of WI to the neck (○) or during a seated control (•)

Values are means ±s.e.m.; n = 7. †P < 0.05 compared with pre-immersion values; *P < 0.05 compared with the corresponding control value. The dotted curve indicates the mathematical approximation of sodium excretion: The asymptote y= 258 (dashed line) indicates the calculated steady-state sodium excretion during prolonged water immersion of subjects on a daily sodium intake of 65-75 mmol.

Figure 3. Intraindividual exponential correlations between renal sodium excretion and plasma concentration of angiotensin II during WI

n = 7; r, 0.73-0.96; P < 0.002 for all.