ALTERATION OF RENAL-FUNCTION OF RATS FOLLOWING SPACEFLIGHT

Following spaceflight, changes in renal function of humans have been s uggested. To assess the effects of readaptation on renal function, uri ne was collected from male rats (similar to 245 g) over a 2-wk period following a 14-day spaceflight. Rats were assigned to three groups: fl ight animals (n = 6), flight controls (n = 6) housed in the flight cag es on the ground, and vivarium controls (n = 5) housed in standard sho e box cages. Animals were placed into individual metabolic cages for u rine collection. Urine output was significantly increased for 3 days f ollowing flight. Excretion rates of Na+ and K+ were increased, resulti ng in an increased osmotic excretion rate. Creatinine excretion rate i ncreased over the first two postflight days. Glomerular filtration rat e increased immediately following spaceflight without changes in plasm a creatinine, Na+, K+, or osmolality. Increased excretion of solute wa s thus the result of increased delivery and a decreased percent reabso rption of the filtered load. Osmolal clearance was increased immediate ly postflight while free water clearance was decreased. In growing rat s, the diuresis after short-duration spaceflight is the result of an i ncrease in solute excretion with an accompanying reduction in free wat er clearance.