Early metabolic and endocrine effects of perorally administered beta-adrenoceptor agonists in calves

Early metabolic and endocrine changes in calves in response to two beta-adrenoceptor agonists in the absence and presence of the beta-adrenoceptor blocking agent propranolol have been studied in calves. The agonists were administered p.o. with milk in different amounts, whereas propranolol was infused i.v. for 10 h. Respiration volume, O2 consumption, CO2 production, respiratory quotient, blood glucose, lactate, non-esterified fatty acids and insulin transiently increased within 2-4 h in a dose-dependent manner, whereas glucagon, adrenaline, noradrenaline, triiodothyronine, urea, albumin and protein did not change significantly. Propranolol completely inhibited the effects on glucose, lactate, non-esterified fatty acids and insulin. Six hours after the administration of the beta-adrenoceptor agonists, the glucose clearance rates following i.v. infusion of glucose were markedly reduced and the glucose decrements in response to an i.v. injection of insulin were much smaller than in the absence of the beta-adrenoceptor agonists. The metabolic changes demonstrate an enhanced glycogenolysis and fat mobilisation, an increased metabolic rate and the development of insulin resistance within 6 h after the administration of the beta-adrenoceptor agonists.