SOMATOTROPIN TREATMENT DOES NOT AFFECT NONESTERIFIED FATTY-ACID RESPONSE TO ADRENERGIC INJECTIONS IN UNDERFED OR OVERFED NONLACTATING COWS

This experiment was conducted to determine the respective effects of b ovine somatotropin (bST) and energy balance on the in vivo responses o f plasma nonesterified fatty acids and glucose to isoproterenol (a non selective beta-agonist) or epinephrine injection in nonlactating nonpr egnant cows. Two groups of adult Holstein cows were either underfed (n = 4) at 75%, or overfed (n = 5) at 150% of maintenance energy require ment, respectively. Cows received or did not receive a subcutaneous in jection of Sometribove (500 mg) during two experimental periods (cross -over design). Adrenergic or placebo injections (4 nmol/kg body weight of epinephrine or isoproterenol or 4 mt of sterile saline) were admin istered intravenously on d 7-9 after bovine somatotropin injection, 1 h before or 3.5 h after feeding for under- or overfed cows, respective ly. Glucose and nonesterified fatty acid responses to each challenge w ere calculated as area under the response curve and above the base lin e, from the time of challenge until 60 min postchallenge. Basal plasma nonesterified fatty acids and their response to adrenergic injections were enhanced by underfeeding. Responses of nonesterified fatty acids to isoproterenol injection were higher than they were to epinephrine injection. Basal plasma glucose was enhanced by bovine somatotropin tr eatment, which increased the glucose response at 5 min after adrenergi c injections. Response of plasma glucose was higher after epinephrine than after isoproterenol injection. Treatment with bovine somatotropin did not change plasma nonesterified fatty acid responses to epinephri ne of isoproterenol injection in under- or overfed cows, at constant e nergy intake, whereas underfeeding modified these responses markedly.