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  • Title: In late pregnancy insulin-dependent glucose transport/phosphorylation is selectively impaired and activation of glycogen synthase by insulin facilitated in skeletal muscles of 24-h starved rats.
    Author: Holness MJ, Sugden MC.
    Journal: Diabetologia; 1999 Jul; 42(7):802-11. PubMed ID: 10440121.
    Abstract:
    AIMS/HYPOTHESIS: We investigated the relation between glucose transport/phosphorylation and glycogen synthase activation in individual rat skeletal muscles in response to moderate hyperinsulinaemia in the absence or presence of hyperglycaemia during pregnancy. METHODS: Rats were studied on day 20 of pregnancy after 24-h starvation, with unmated rats as controls. Insulin and glucose were infused into conscious rats through an indwelling cannula as specified. Glucose transport/phosphorylation was assessed in vivo using 2-deoxy-[1-3H]glucose. Glycogen synthase activity was measured in muscle extracts < or = 10 mmol/l glucose-6-phosphate. RESULTS: In unmated rats, stimulation of glucose transport/phosphorylation occurred in response to euglycaemic-hyperinsulinaemia in all muscles studied but activation of glycogen synthase was not observed. Muscle glucose transport/phosphorylation rates during euglycaemic-hyperinsulinaemia after 24-h starvation were lower in pregnant compared with unmated rats, whereas glycogen synthase activation by insulin occurred in two of three fast-twitch muscles of pregnant rats. When insulin and glucose concentrations were matched between the 24-h starved unmated and pregnant groups through variable glucose infusion (15 min), glycogen synthase activities in fast-twitch muscles did not differ between unmated and pregnant groups. The response of glycogen synthase to hyperglycaemia in slow-twitch muscle was, however, greater in the pregnant group. CONCLUSION/INTERPRETATION: Glycogen synthase activation in slow-twitch muscle in response to hyperinsulinaemia after 24-h starvation is enhanced in late pregnancy but the response is critically dependent on glycaemia. Pregnancy is, nevertheless, associated with reduced muscle glucose transport/phosphorylation. This disassociation ensures that available glucose is directed towards the fetus rather than the mother under conditions of moderate hyperinsulinaemia, for example during refeeding after starvation.
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