Effects of hyperinsulinemia on lactose secretion and glucose uptake by the goat mammary gland.

Abstract

AbstractHove, K. Effects of hyperinsulinemia on lactose secretion and glucose uptake by the goat mammary gland. Acta physiol. scand. 1978. 104. 422–430.Lactose secretion by goat mammary glands was studied after intra‐arterial infusions of insulin and/or glucose causing rises in plasma insulin concentrations in mammary venous blood of about 3–5 mg/ml. Such levels are sufficient to strongly stimulate insulin sensitive processes when present in the systemic circulation. Two goats with mammary glands in situ and two with one of the glands autotransplanted to the neck were used for the experiments. Increasing the insulin concentration in blood to the mammary gland induced a decrease in lactose yields during a 3 h infusion (p < 0.02). Simultaneously arterial plasma glucose decreased by 15–20 mg/100 ml to about 50 mg/100 ml. When the systemic hypoglycemic effect of the insulin infusion was offset by a simultaneous intra‐venous infusion of glucose, no significant change in lactose secretion was observed during 8 hours of hyperinsulinemia. No change in mammary glucose uptake as measured by mammary blood flow x mammary arterio‐venous glucose differences could be detected. (Average glucose uptake for 2 h before infusion: 30.9 mg/min; during 8 h of infusion: 31.2 mg/min.) It may be concluded that increased levels of insulin in the blood perfusing the mammary gland did not affect mammary glucose uptake or lactose synthesis as long as blood glucose was maintained at normal levels. The results therefore indicate that the glucose turnover in mammary glands, which in high yielding dairy ruminants represents the main organ of glucose utilization in the body, is in fact independant of changes in plasma insulin concentrations.