Metabolic and physiological effects of adrenoceptor agonists and antagonists in the horse

In the horse the effect of the adrenergenic agonists adrenaline, phenylephrine and salbutamol on haematocrit, plasma free fatty acid, glycerol and lactate levels were investigated. Effects on heart rate, sweating and muscle tremor were also studied. The effects of administration of the adrenoceptor antagonists propranolol, metoprolol, H35/25 and acepromazine on adrenaline-induced changes were examined. The results obtained with these agonists and antagonists suggest that the lipolysis and hyperglycaemia are mediated via beta-adrenoceptors. It appears that both beta1 and beta2 subtypes are involved. Muscle glycogenolysis, muscle tremor and sweating were mediated via beta2-adrenoceptors. Although salbutamol caused an elevation in haematocrit the other results support the alpha-mediation of adrenaline induced increases in haematocrit.