Haemodynamic effects of the intravenous administration of growth hormone in anaesthetized pigs

Administration of growth hormone in humans has been reported variably to affect arterial blood pressure and ventricular contractility. The present study was undertaken in anaesthetized pigs to establish whether increases in the blood levels of growth hormone primarily affect haemodynamic variables and to determine the mechanisms involved. In pigs anaesthetized with pentobarbitone sodium, left circumflex or anterior descending coronary blood flow was measured with an electromagnetic flowmeter. In a first group of 23 pigs, growth hormone administration (0.05 IU kg^-1 i.v.) increased aortic blood pressure and reduced coronary blood flow when heart rate and aortic blood pressure were held constant. These responses were augmented by graded increases in plasma levels of growth hormone. The mechanisms of the above responses were studied in a second group of 29 pigs and involved β₂- adrenergic receptors since they were abolished by propranolol or butoxamine but not by atropine, phentolamine or atenolol. The present study showed that administration of growth hormone in anaesthetized pigs primarily increased aortic blood pressure and vasoconstricted the coronary circulation. The mechanisms of these responses involved β₂-adrenoceptor effects.