Effects of maternal hyperglycemia on fetal renal function in sheep

The effects of maternal hyperglycemia on fetal renal function were investigated in 10 chronically catheterized fetal sheep after the infusion of 100 g of glucose into the ewe over 30 min. Fetal blood glucose levels rose (P less than 0.001) within 15 min of completing the glucose infusion from 15.75 +/- 2.8 to 195.4 +/- 18 (SE) mg/dl (n = 10). There was a significant increase in fetal glomerular filtration rate (P less than 0.05) from 2.73 +/- 0.41 to 3.65 +/- 0.40 (SE) ml/min (n = 10) within 1.5 h of the infusion of glucose into the ewe. Urine flow rate increased from 0.38 +/- 0.06 to 0.63 +/- 0.12 (SE) ml/min (n = 10, P less than 0.001), and sodium excretion increased from 18.42 +/- 7.21 to 38.4 +/- 13.7 (SE) mumol/min (n = 10, P less than 0.002) within 2.5 h of the infusion of glucose into the ewe. The fraction of the filtered load that was excreted (urine flow rate divided by glomerular filtration rate) also increased (P less than 0.01) as did the fraction of the osmolar load (P less than 0.002). Glycosuria occurred in all fetuses within 30 min of the infusion of glucose into the ewe, and glucose excretion reached 26.16 +/- 12.36 (SE) micrograms/min (n = 8) after 1.5 h. These findings of diuresis, natriuresis, and glycosuria in response to hyperglycemia are evidence that an increased delivery of fluid into the amniotic cavity might occur after a rise in fetal plasma glucose levels.