The metabolic and endocrine effects of circulating catecholamines in fetal sheep

1. Adrenaline and noradrenaline have been infused into the fetal sheep to produce plasma concentrations comparable to those seen during hypoxia. The effects have been compared with those of isoprenaline and methoxamine and the sensitivity to beta- and alpha-adrenergic antagonists has been followed. 2. Adrenaline caused an alpha-mediated increase in blood glucose that is associated with a fall in plasma insulin concentration. It also caused a beta-mediated increase in plasma lactate, free fatty acid and amino acid concentrations. 3. Noradrenaline was much less effective than adrenaline at eliciting metabolic responses. It had not cause a significant change in plasma glucose concentration, although this was associated with a small increase in plasma insulin concentration. It caused a small rise in the concentration of lactate and free fatty acids in fetal plasma but had no effect on plasma amino acids. 4. The beta- and alpha-adrenergic antagonists propranolol and phentolamine alone were without effect on any of the plasma metabolites or hormones assayed. Isoprenaline increased plasma glucose, lactate, free fatty acid, alanine and insulin concentrations, while methoxamine only increased plasma glucose and lactate, and this was associated with a fall in insulin concentration. 5. The concentration of ACTH in fetal plasma was increased by adrenaline and to a lesser extent by noradrenaline and methoxamine; these were blocked by phentolamine. Isoprenaline also caused a small increase in ACTH. There were no corticosteroid changes associated with the increase in ACTH. 6. The results have been discussed in relation to the adrenergic and pancreatic control of metabolism in the fetal sheep.