The effect of maternal fluid intake on the volume and composition of fetal urine.
The effects on fetal renal function of restricting maternal water intake to 1 l/day for 6 days was investigated in 7 chronically-catheterized fetuses (gestation age 118-131 days). Restriction of water intake caused a significant decrease in maternal urine flow rate and significant increases in maternal plasma and urinary osmolality. Fetal renal function was investigated on the third and sixth days of the period of restricted maternal intake of water. Urine flow rate from the fetus was depressed significantly, and urinary osmolality increased significantly. The glomerular filtration rate remained unchanged, and free water clearance was decreased. These changes indicate increased water reabsorption in the distal parts of the nephron, probably consequent upon increased circulating levels of antidiuretic hormone. In 3 fetuses whose mothers subsequently had free access to water, these changes in urine flow rate and free water clearance that occurred during water restriction were reversed. There was an inverse correlation between maternal plasma osmolality and fetal free water clearance corrected for glomerular filtration rate. It is concluded that when water intake by a pregnant animal is restricted, the availability of water to the fetus is reduced and fetal sheep respond by producing a concentrated urine.
D000818:Animals; D001769:Blood / Q000378:metabolism; D004326:Drinking; D005260:Female; D005333:Fetus / Q000378:metabolism*; D007668:Kidney / Q000196:embryology / Q000502:physiology; D009318:Natriuresis; D009994:Osmolar Concentration; D011247:Pregnancy; D012756:Sheep / Q000196:embryology; D014556:Urine / Q000032:analysis*; D014868:Water Deprivation