THE MYOCARDIAL EFFECTS OF FENOTEROL, ISOPRENALINE AND SALBUTAMOL IN NORMOXIC AND HYPOXIC SHEEP

Three groups, each of four sheep, were randomly allocated under blinde d conditions to receive the beta-adrenoceptor agonists, salbutamol, fe noterol or isoprenaline, in doses of 0.5, 2, 8, 32 and 128 mu g/kg int ravenously at 15-minute intervals. A separate group of four animals re ceived equal volumes of saline. Heart rate was recorded immediately pr ior to each drug administration and serum potassium was measured. Thre e to 4 days later the experiment was repeated during induced systemic hypoxia and the animals then necropsied. All the agonists produced sig nificant increases in heart rate. During hypoxia, lower heart rates we re recorded than in the normoxic experiments. Under conditions of hypo xia, all the beta-agonists produced significant hypokalaemia. Sterile saline had no effect on either heart rate or serum potassium levels. A t necropsy, myocardial lesions were found in animals receiving all thr ee beta-agonists. Subendocardial haemorrhage was consistently seen in all animals receiving fenoterol. Multifocal myonecrosis of 3-4 days du ration was present in the left ventricle of all animals receiving feno terol, in two receiving isoprenaline and in two receiving salbutamol. The lesions were most severe in the papillary muscle and were visible grossly in one animal given fenoterol and one given isoprenaline. No l esions were found in the control animals.