Plasma catecholamines and blood substrate concentrations: studies in insulin induced hypoglycaemia and after adrenaline infusions

Abstract

Plasma adrenaline-blood glucose interrelationships in insulin-induced hypoglycaemia in man have been studied using a sensitive double-isotope derivative method for adrenaline estimation. Plasma adrenaline reached a peak of 1.24 ng/ml at 45 minutes after insulin while blood glucose reached a nadir of 22 mg/100 ml at 30 minutes. There was a strong correlation both between the rise in adrenaline and the degree of hypoglycaemia and between the rise in adrenaline and the post-hypoglycaemic rise in glucose. Plasma noradrenaline rose from 0.29 to 0.59 ng/ml, the rise correlating with the rise in adrenaline. Changes in pulse rate preceded and were unrelated to changes in plasma catecholamines. Fuel mobilisation in response to adrenaline infusion (6 mug/min. for 20 min.) in normoglycaemic man was also studied. Plasma adrenaline concentration rose from a mean of 0.02 ng/ml to 0.71 ng/ml while plasma noradrenaline concentration was unchanged. Blood glucose rose from 71 to 98 mg/100 ml while plasma insulin decreased from 11 to 8 muU/ml. Blood lactate rose by 0.85 mM while pyruvate concentration remained unchanged. Blood glycerol concentration rose twofold and ketone body concentration threefold but there was little change in the concentrations of the glucogenic amino acids, alanine, glutamate and glutamine. Both the 3-hydroxybutyrate/acetoacetate ratio and the lactate/pyruvate ratio rose implying a more reduced intracellular state due presumably to increased hepatic fatty acid oxidation. It is concluded that adrenaline enhances the recycling of lactate and spares glucose through the mobilitsation of lipids but that amino acids are little affected.