Urinary ANP, ADH, and electrolyte excretion during saturation-excursion diving to pressures equivalent to 250 and 300 m.

Four male divers were exposed to an environment of 26 and 31 atm abs He-O2 for 2 days. Urine was collected during the day (0700-1900 h) and at night (1900-0700 h) before (predive 1 atm abs air), during, and after (decompression and postdive 1 atm abs air) the exposure. Urine flow increased markedly and was mostly attributable to the urine flow during 1900-0700 h. The secretion of atrial natriuretic polypeptide (ANP) increased only at night during hyperbaria. On the other hand, the secretion of antidiuretic hormone (ADH) was suppressed, but increased during compression and the early phase of hyperbaric exposure before it decreased. Linear regression analysis showed that urinary excretion of ANP was correlated significantly with urine flow (r = 0.88, P less than 0.01) and that excretion of ADH negatively correlated with urine flow (r = -0.61, P less than 0.01). Urinary excretion of Na, Cl, Ca, and Mg increased significantly at night during hyperbaria, whereas there was no consistent change in the excretion of K and P. These results suggest that both stimulated ANP secretion and suppressed ADH secretion correlate with the increase of urine and that nocturia is mostly attributable to stimulated ANP secretion. We observed that urinary excretion of ANP increased significantly as early as during the compression phase, which suggested that ANP plays a decisive role in the early diuresis.