Progressive gross changes in renal medullary composition in pregnant rats.

The biochemical composition of the renal medulla and the blood pressures of pregnant rats and nonpregnant controls were compared on days 15, 18, 20, and 22 of pregnancy. Deoxyribonucleic acid and protein content of the renal medulla changed together with the tissue weight (wet weight) during gestation except on day 20 when a slight increase in protein was observed. However, the glycerophospholipids (phosphatidyl ethanolamine, phosphatidyl choline, and phosphatidyl serine) and sphingomyelin showed significant increases throughout the latter stages of pregnancy with the maxima in most cases occurring on day 20 of the gestation period. Medullary hypertrophy and increased lipid content per cell coexist with the decrease in blood pressure and may indicate peak activity in production of antihypertensive renal lipids.