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Insulin Response to Glucose in Estrous and Diestrous Obese and Lean Heifers

Cornell University², Ithaca, NY 14853

Abstract

This study determined if the insulin and glucose responses to glucose infusion in obese (n = 4) and lean (n = 4) Holstein heifers were affected by stage of the estrous cycle. Glucose (.35 g/kg) was infused within 2 min into the jugular veins of heifers during diestrus (d 15) and at the subsequent estrus (d 0). Concentrations of insulin and glucose were determined in jugular venous serum obtained from blood samples collected at 60, 45, 30, 15 and 1 min before and at 2.5, 5, 10, 15, 20, 30, 40, 50, 60, 80, 100, 120, 140, 160, 180, 210 and 240 min after glucose. Mean (± SE) pretreatment concentrations of glucose (mg/100 ml) in obese (68 ± 1.9) and lean (71 ± 2.5) heifers were unaffected by body condition and stage of the cycle. Mean (± SE) pretreatment concentrations of insulin (µU/ml) were unaffected by stage of the cycle but were higher (P<.05) in obese (33 ± 3.6) than in lean (18 ± 2.7) heifers. Body condition affected the insulin response with greater absolute concentrations (P<.01) and total (P<.005) response areas of insulin in obese than in lean heifers. Kinetics of the injected glucose were unaffected by body condition and stage of the cycle. However, there was interaction (P<.05) between these main effects on the acute insulin response and glucose kinetics as follows: the mean (± SE) acute insulin response area (0 to +15 min; µU·ml^–1·min^–1) was greater (P<.025) in estrous (2,559 ± 65) than in diestrous (1,929 ± 64) obese heifers, while the mean (± SE) fractional removal rate (k; .034 ± .004 vs .048 ± .001 min^–1) and biological half-lives (t; 21.7 ± 3.5 vs 14.5 ± .4 min) for glucose were slower (P<.025) in estrous obese than in estrous lean heifers. Estrus in obese heifers enhanced the acute insulin response to glucose and decreased the responsiveness of body tissues to the glucoregulatory effects of insulin.

¹ Address correspondence to Dr. Joseph P. McCann, Dept. of Physiol., New York State College of Veterinary Medicine.

² Diagnostic Endocrinol. Lab., New York State College of Vet. Med.