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 haema-tocrit, plasma free fatty acid, glycerol, glucose 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, H32/25 and acepro-mazine on adrenaline-induced changes were examined. The results obtained with these agonists and antagonists suggest that the lipolysis and hyperglycaemia are mediated via β-adrenoceptors. It appears that both 3, and β2 subtypes are involved. Muscle glycogenosis, muscle tremor and sweating were mediated via β2-adrenoceptors. Although salbutamol caused an elevation in haematocrit the other results support the α-mediation of adrenaline induced increases in haematocrit.