Does gender influence human cardiovascular and renal responses to water immersion?

We hypothesized that women and men exhibit similar cardiovascular and renal responses to thermoneutral water immersion (WI) to the neck. Ten women and nine men underwent two sessions in random order: 1) seated nonimmersed for 5.5 h (control) and 2) WI for 3 h, with subjects seated nonimmersed for 1. 5 h pre- and 1 h postimmersion. We measured left atrial diameter, heart rat e, arterial pressure, urine volume and osmolality, and urinary endothelin, urodilatin, sodium, and potassium excretion. No significant difference exis ted between groups in cardiovascular responses. The groups also exhibited m ostly similar renal responses to immersion after adjustment for body mass. However, female urodilatin excretion per kilogram during immersion was over twofold that of men, and the female kaliuretic response to immersion was d elayed and less pronounced relative to that in men. Men may excrete more po tassium than women during immersion because men possess greater lean body m ass (potassium per kilogram). Results obtained in men during WI may be caut iously extrapolated to women, yet urodilatin and potassium responses exhibi t gender differences.