Sympathoadrenal and other endocrine and metabolic responses to hypoglycaemia in the fetal foal during late gestation

Abstract

SUMMARYIn the present study, ten insulin challenge tests were carried out on nine chronically catheterized fetal foals between 253 and 314 days gestation (term > 320 days). Changes in fetal plasma concentrations of glucose, catecholamines, cortisol, ACTH, free fatty acid (FFA) and lactate were measured before and after a bolus dose of insulin (0-5-2.0 u/kg i.v.). Fetal blood gases, pH, haemoglobin levels and heart rate were measured throughout the 2-3 h experimental period. The fetuses fell into two distinct groups on the basis of proximity to delivery and basal plasma cortisol and catecholamine levels. Those within 2-10 days of delivery after 300 days (group 2, number of experiments (n) = 4) had plasma cortisol and noradrenaline concentrations which were significantly higher (P <0.05) than the corresponding values in fetuses sampled earlier in gestation or at least 2 weeks before foaling (group 1, n = 6). Although insulin administration resulted in a 50% fall in plasma glucose in all animals, group 2 showed significantly greater increases in plasma noradrenaline than group 1. In neither group were there detectable changes in plasma adrenaline. In group 2, increases in plasma cortisol were seen following insulin, whereas no cortisol changes were observed in group 1, despite rises in plasma ACTH. Insulin administration also led to acidosis and increases in heart rate and plasma lactate and FFA levels in all fetuses studied. However, only group 2 became consistently hypoxic during the insulin challenge. No significant changes in plasma glucose or any of the other parameters were observed in the fetuses after saline administration (n = 5). These findings suggest that hypoglycaemia activates the sympathoadrenal system in the fetal foal from 75 % of gestation but has relatively little effect on the fetal pituitary-adrenocortical axis until much closer to term.

Chronic late-gestation hypoglycemia upregulates hepatic PEPCK associated with increased PGC1α mRNA and phosphorylated CREB in fetal sheep

“…No differences were found between treatment groups, which are listed on x-axis. concentrations in response to hypoglycemia have been described before in a variety of late-gestation and neonatal mammals (13,28,62). In the sheep, like many mammalian species, liver glycogen content increases during the later part of gestation (61).…”

Endocrine adaptations in the foal over the perinatal period

“…1982; Silver et al . 1984; Silver and Fowden 1995). It remains suppressed for the next 2 days if the foal survives, despite high endogenous ACTH concentrations (Silver et al .…”

Comparative aspects of prepartum maturation: Provision of nutrients

“…Furthermore, the activity of adrenal phenyl-N-methyl transferase (PNMT) increases towards term and, hence, circulating adrenaline concentrations rise in late gestation. In the foal, activation of adrenomedullary adrenaline secretion occurs very close to term with little, if any, adrenaline secretion in response to hypoglycaemia before birth but a rapid adrenaline increment in hypoglycaemic neonates (Silver et al, 1987;Silver and Fowden, 1995). Certainly, at birth, the increment in plasma catecholamine concentrations in the foal is similar in magnitude to that seen in other domestic species (Table 1).…”