INSULIN-RECEPTOR BINDING AND TYROSINE KINASE-ACTIVITY IN SKELETAL-MUSCLE FROM NORMAL PREGNANT-WOMEN AND WOMEN WITH GESTATIONAL DIABETES

Objective: To ascertain whether the decreased glucose tolerance and in sulin resistance found in normal and gestational diabetic pregnancy mi ght be associated with changes in insulin receptor function. Methods: Eight nonpregnant healthy women (nonpregnant controls), eight healthy pregnant women (pregnant controls), and eight women with gestational d iabetes were investigated. All were non-obese. Muscle biopsies were ob tained from the vastus lateralis muscle, and insulin binding and tyros ine kinase activities in partially purified skeletal muscle insulin re ceptors were studied. The pregnant controls were investigated in late pregnancy, and the women with gestational diabetes were investigated a t the time of diagnosis of gestational diabetes. A further examination was carried out 2 months after delivery. Results: Insulin binding at tracer insulin concentration (60 pmol/L) was diminished in women with gestational diabetes compared to nonpregnant controls (P < .05), where as normal pregnant women did not differ from the other two groups. Pos tpartum, no differences in insulin binding were found between the grou ps. Basal and maximal tyrosine kinase activities toward the exogenous substrate poly(Glu4Tyr1) were the same in nonpregnant controls, pregna nt controls, and women with gestational diabetes. Postpartum, no diffe rences in tyrosine kinase activity were found among the groups. Moreov er, no significant differences in insulin binding or tyrosine kinase a ctivity were found comparing pregnancy and postpartum values within th e groups. Conclusion: The insulin resistance found in normal and gesta tional diabetic pregnancy is not likely to be caused by a defective in sulin receptor tyrosine kinase, whereas decreased insulin receptor bin ding might have some pathogenic importance in gestational diabetes.