Effects of placental lactogen and progesterone on insulin stimulated glucose metabolism in rat muscles in vitro.

The short term effects of ovine placental lactogen and progesterone have been studied on skeletal muscle glucose metabolism in order to determine their respective roles in pregnancy-induced insulin resistance. The rates of hexose transport, glycogen synthesis, and glycolysis were measured in vitro by incubating stretched soleus, extensor digitorum longus (EDL) and epitrochlearis from virgin rats. When incubated in plasma from late pregnant rats, EDL glucose metabolism was reduced by 30% when compared to EDL incubated in plasma from virgin rats despite similar glucose (8 mM) and insulin (200 microU/ml) concentrations. Ovine placental lactogen (5 X 10(-7) M) had no effect on EDL glucose metabolism either in the basal state or after stimulation by insulin (100 microU/ml). Progesterone (10(-4) M) induced an inhibition of hexose transport, glycogen synthesis and glycolysis rates up to 60% in the absence or in the presence of insulin in all muscles studied. In conclusion, the plasma of late pregnant rats contains factors responsible for a decreased rate of glucose metabolism in incubated skeletal muscle. This is mimicked by progesterone but not by ovine placental lactogen added to the incubation medium.