Insulin-independent glucose uptake in growth hormone treated dairy cows

Our aim was to determine the effect of growth hormone on non-insulin-mediated glucose disposal in lactating dairy cows. Following 5 d of subcutaneous injections of either saline or growth hormone, insulin, somatostatin or insulin plus somatostatin were infused for 2 h each, in a series of experiments. Coincident with this, unlabelled glucose was infused at a variable rate to maintain a constant plasma glucose concentration. Glucose, doubly labelled with deuterium, was also infused for the calculations of glucose turnover. Plasma insulin levels were reduced to nearly zero by the infusion of somatostatin; under such conditions whole body glucose disposal should be non-insulin-mediated. Dairy cows treated with growth hormone, which had significantly increased milk yields on the day before the experimental infusions, did not have different levels of whole body non-insulin-mediated glucose disposal when expressed in absolute terms. Growth hormone did not affect non-mammary non-insulin-mediated glucose uptake estimated by calculation. Growth hormone significantly inhibited insulin-mediated glucose uptake when plasma insulin levels were elevated. Glucose uptake during insulin plus somatostatin infusion was not significantly different from that of the insulin only infusion.