Contribution of vagal pathways to the renal responses to head out immersion in the nonhuman primate

Studies were carried out to determine the contribution of cardiopulmonary receptors to the renal responses to head-out water immersion in the nonhuman primate. Immersion to the suprasternal notch was associated with significant increases in central venous pressure, urine flow, and sodium excretion. The increased sodium excretion was due primarily to a significant increase in the percent of the filtered sodium excreted. Deoxycorticosterone acetate (DOCA) and antidiuretic hormone (ADH) had no substantial effects on these responses. The finding of a vasopressin-resistant hyposthenuria is consistent with the natriuresis of immersion being due, at least in part, to a decrease in sodium reabsorption proximal to the diluting segment, possibly the proximal tubule. Bilateral cervical vagotomy had no substantial influence on the renal responses to immersion, demonstrating that cardiopulmonary receptors whose axons traverse the vagus nerves are not necessary for the homeostatic adjustments to central hypervolemia in the primate. Since the renal and cardiovascular responses of the primate to immersion are essentially the same as those seen in man, it is probable that vagal pathways also are not necessary in man. However, it is possible that sympathetic afferents are involved in the natriuresis observed in the primate during immersion.