Effect of insulin-induced maternal hypoglycemia on glucose turnover in maternal and fetal sheep
Anand, R.S.; Ganguli, S.; Sperling, M.A.
American Journal of Physiology 238(6): E524-E532
1980
ISSN/ISBN: 0002-9513 PMID: 6992595 Document Number: 163590
The effect of insulin.cntdot.kg-1 per h) to M for 2 h raised M I levels from 15 .+-. 2 .mu.U/ml (mean .+-. SE) to a peak of 175 .+-. 10 .mu.U/ml. Maternal glucose fell from 61 .+-. 2.0 to 29 .+-. 2.0 mg/dl. Simultaneously, F glucose concentration fell from 21.7 .+-. 1.3 to 11.4 .+-. 0.7 mg/dl, whereas I remained constant at 8 .+-. 2 .mu.U/ml. When M was infused with labeled glucose, the ratio of M-to-F glucose specific activity (SA) was statistically 1.0 both before and during I infusion. F glucose flux apparently was derived entirely from the M and there was no significant glucose production by F. At steady state, M glucose production (Ra) and utilization (Rd) were 148 .+-. 14 mg/min. After the start of I infusion, Ra fell to 114 .+-. 12 mg/min, whereas Rd rose to 196 .+-. 14 mg/min at 30 min (P < 0.05 for each). Thereafter, both Ra and Rd gradually returned to the basal level, reaching preinsulin values by 90 min and remaining unchanged despite ongoing I infusion and persistent hypoglycemia. In contrast, in F both Ra and Rd declined continuously and in parallel from 33.2 .+-. 3.5 to 19.1 .+-. 2.3 mg/min as maternal glucose fell, indicating a decrease of over 40% in the placental transfer of glucose from M to F. When the F was infused with labeled glucose, significant amounts of labeled glucose appeared in the M plasma. The ratio of M-to-F glucose SA indicated that 12 .+-. 2% (16 .+-. 3 mg/min) of M glucose turnover was derived from the F to the M transfer; this constituted 44 .+-. 5% of F glucose turnover. During the I infusion to M, despite significant F hypoglycemia, the fractional transfer to glucose from F to M remained constant, although in absolute amounts it decreased to 9 .+-. 2 mg/min. In sheep the F glucose apparently is completely dependent on M supply during M euglycemia or during 2 h of I-induced M hypoglycemia, with no evidence of compensatory glucose production by F. Glucose transfer across the placenta is bidirectional; although net flux is from M to F, there is substantial transfer from F to M that continues during F hypoglycemia. Continuous I infusion exerts only transient effects on Ra and Rd in M in the presence of sustained low blood glucose.