METABOLIC RESPONSES TO HYPERINSULINEMIA UNDER GLUCOSE-POTASSIUM-AMINO ACIDS CLAMP IN LACTATING AND NONLACTATING GOATS

The present experiment was undertaken to investigate adaptations to insulin action on metabolism during lactation by using plasma concentrations of beta hydroxybutyrate (beta OH) free fatty acids (FFA) and lactate (L) as indicators. The study included three groups each of four goats. One group was used at 12 to 31 days post partum (early lactation), one group at 98. to 143 days post partum (mid lactation) and one group al 1 year post partum (dry period). For a given physiological state, each goat was examined four times to study the effect of insulin infused for 2.5 h at two rates, medium (0.36 nmol/min) followed by high (1.79 nmol/min) in two protocols: under normal aminoacidaemia in study 1 followed by hyperaminoacidaemia in study 2. Appropriate amino acid infusions were used to blunt insulin-induced hypoaminoacidaemia under eukaliaemic and euglycaemic clamp conditions or to create hyperaminoacidaemia and maintain this state tinder insulin treatment. In the basal state beta OH (P < 0.05), mid lactation) and FFA (P < 0.05 early lactation) were higher during lactation than in the dry period. Plasma L was unmodified. Insulin infusion always resulted in a decrease in beta OH levels (P < 0.05). In both studies, the change in beta OH concentration as a function of changes in plasma insulin (an index of insulin sensitivity) was greater during early lactation than in the dry period (P < 0.05); this was also the case of mid lactation in study 2. Insulin infusion decreased plasma FFA during early lactation and in the dry period in study 1 (P < 0.05), and there was a trend for insulin sensitivity to be greater during early lactation. In both studies insulin infusion did not affect plasma L in lactating goats whereas plasma L was increased in dry animals (P < 0.05). The results demonstrate that during early lactation, compared with the dry period, there is an increased ability of insulin to lower beta OH and FFA concentrations. These effects were not altered by increasing plasma amino acid concentrations during insulin infusion.