Autonomic modulation of insulin levels in foetal sheep

The autonomic nervous system plays an important part in metabolic and circulatory adaptation of the foetus to changes in its intrauterine environment and after delivery. Foetal and neonatal glucose metabolism and insulin secretion are influenced by changes in humoral catecholamine levels as they may occur during asphyxia. To assess the role of neuronal and humoral sympathetic activity in foetal endocrine pancreatic regulation, chronically catheterized foetal sheep near term were chemically sympathectomized with 6-hydroxydopamine. Experiments were carried out in unanaesthetized foetal sheep in utero in the absence of uterine contractions. Insulin and glucose levels, blood gases, acid-base status and catecholamines were measured before, during and after a 2 min occlusion of uterine blood flow caused by mechanical constriction of the maternal aorta. Pancreatic blood flow was determined using radioactive labelled microspheres. During normoxaemia, insulin levels, pancreatic blood flow and glucose transport to the organ in sympathectomized foetuses were elevated compared with intact animals, whereas glucose concentrations did not show any significant differences. After the onset of asphyxia humoral catecholamine levels rose significantly in both groups. Insulin concentrations in the plasma of both intact and sympathectomized foetuses were no longer different indicating both indirect (blood flow and humoral catecholamine related) and direct (neurally mediated) sympathetic effects on pancreatic beta cells.