Effect of insulin on fat metabolism during and after normal pregnancy

Whereas development of resistance to the action of insulin on glucose metab olism during gestation has been recognized, it is presently not known wheth er there is also resistance to the action of insulin on lipid metabolism. W e have, therefore, examined the effect of physiological hyperinsulinemia (d uring euglycemic-hyperinsulinemic clamping) on free fatty acid (FFA) turnov er in seven nondiabetic overweight or obese women during and after pregnanc y. Basal rates of FFA release, oxidation, and reesterification and basal pl asma FFA concentrations were not significantly different from each other du ring the 2nd and 3rd trimester of pregnancy and postpartum During euglycemi c-hyperinsulinemic (similar to 500 pmol/l) clamping, however, lipolysis was significantly less inhibited during the 3rd trimester (from 7.0 +/- 0.9 to 4.9 +/- 0.9 mu mol.kg(-1). min(-1), -30%) than during the 2nd trimester (f rom 8.4 +/- 0.6 to 4.1 +/- 0.9 mu mol.kg(-1).min(-1), -51%) and postpartum (from 8.5 +/- 1.1 to 4.2 +/- 0.6 mu mol.kg(-1).min(-1), -51%). Similarly, f at oxidation was not inhibited at all (from 3.5 +/- 0.3 to 3.8 +/- 0.5 mu m ol.kg(-1).min(-1)) during the 3rd trimester but was suppressed by 51% (from 3.9 +/- 0.2 to 1.9 +/- 0.3 mu mol.kg(-1).min(-1)) during the 2nd trimester and by 38% (from 2.6 +/- 0.7 to 1.6 +/- 0.5 mu mol.kg(-1).min(-1)) postpar tum. These data demonstrated that resistance to the action of insulin on li polysis and on fat oxidation developed during late gestation and disappeare d postpartum.