Effect of chronic growth hormone and hyperinsulinemic euglycemia on endogenous glucose production and utilization in periparturient dairy cows

Abstract

Twenty-one periparturient Holstein cows were used to assess the effects of chronic intramuscular growth hormone (GH) and hyperinsulinemic euglycemia (HE) on glucose rate of appearance (Ra) into plasma. Cows were administered intramuscular GH (40 mg) or saline (CTL) daily for 96 h beginning either 25 d prepartum (GH, n=5; CTL, n=6) or 5 d postpartum (GH, n=6; CTL, n=4). Glucose Ra into plasma was determined using tracer methodologies on d 4 of treatment during basal condition and again during a period of HE. The period of HE was initiated immediately after the basal period and lasted for 4 h. It involved a 2 μg*kg−1 infusion of bovine insulin with maintenance of glycemia within 10% of the pre-insulin baseline by intrajugular infusion of exogenous glucose. The HE decreased endogenous glucose Ra to a greater extent postpartum than it did prepartum (P<0.001). Chronic GH increased endogenous glucose Ra (P=0.03); however there were no interactions of GH with physiological state (pre- vs. postpartum) or degree of suppression of endogenous Ra by HE. The amount of exogenous glucose needed to maintain euglycemia during HE was not affected by GH (P≥0.20). In conclusion, there were no interactions of chronic GH with insulin relative to glucose metabolism. However, insulin did have differential effects on glucose metabolism during the pre-and postpartum periods. Project funded by internal sources.