Antinatriuretic Kidney Response to Weightlessness

Abstract

We have tested the effects of weightlessness on renal function in one subject who flew on the recent week-long Russian-German MIR'92 space mission. Urine flow, renal sodium excretion, and the excretion of urodilatin were measured during the first and last days of the flight. Our results demonstrated, in contrast to expectations,that urine flow and sodium excretion during weightlessness were actually lower than the values obtained during preflight measurementsThese results therefore areinconsistent with the commonly held hypothesis that weightlessness induces a diuresis and natriuresis in human subjects. It would seem that further studies are necessaryto resolve this issue and to determine whether currently used ground- based models of weightlessness correctly predict physiological adaptations that occur during space flight.