Ontogeny and ultradian rhythms of adrenocorticotropin and cortisol in the late-gestation fetal horse

Abstract

Fetal maturation and the timing of parturition in both sheep and primates are thought to be controlled by the hypothalamic-pituitary-adrenal axis but little is known about the endocrinology of the equine fetus. We investigated the ontogeny of plasma concentrations of adrenocorticotropic hormone (ACTH), cortisol and corticosteroid binding capacity in the late-gestation fetal horse. We also wished to determine whether there is ultradian rhythmic release of ACTH and cortisol in fetal horses and we compared fetuses to maternal and non-pregnant adult horses. Six fetuses, 278-304 days gestation (term approximately 335), were catheterized and sampled daily until delivery. Mean (+/- S.E.M.) ACTH concentrations increased significantly from 159 +/- 21 to 246 +/- 42 pg/ml over the last 2 days before parturition. Fetal cortisol increased significantly from 3.1 +/- 1.0 to 13.4 +/- 3.7 ng/ml (mean +/- S.E.M.) over the last 9 days before delivery. The slope of regressions for ACTH and cortisol concentrations with respect to time were positive in all subjects and statistically significant in 3 of 6 for ACTH and 5 of 6 for cortisol. Fetal corticosteroid binding capacity declined from 49.5 +/- 20.5 to 16.1 +/- 2.2 ng/ml (mean +/- S.E.M.) over the last 10 days before parturition. However, the greatest changes in ACTH, cortisol and corticosteroid binding capacity occurred very late in gestation, during the last 48 to 72 h before parturition.(ABSTRACT TRUNCATED AT 250 WORDS)

Maternal dexamethasone treatment in late gestation induces precocious fetal maturation and delivery in healthy Thoroughbred mares

“…The different outcomes may reflect the degree of fetal adrenocortical maturation and circulating concentrations of fetal cortisol at the time of dexamethasone treatment. Usually, fetal cortisol concentrations remain low until the last few days before delivery when there is a marked rise associated with fetal maturation (Cudd et al . 1995; Fowden and Silver 1995).…”

“…Peripheral progestagen concentrations increased within 24 h of the first dexamethasone administration. Normally, progestagen concentrations rise during the last few weeks of gestation driven by increasing output of pregnenolone from the fetal adrenal glands and upregulation of fetal ACTH secretion (Cudd et al . 1995; Ousey 2006).…”

Review of the reproductive endocrinology of the pregnant and parturient mare

“…In contrast to the historic uncertainty over hormonal changes in maternal blood before foaling, it is generally agreed that parturition in mares is associated with an increase in cortisol in fetal blood [159,160], accelerating in the last couple of days [134]. In contrast, the increase in fetal cortisol is initiated much earlier in livestock species, beginning from a few days to a few weeks before term [161].…”

Transcriptional regulation of episodic glucocorticoid secretion

“…Studies in humans (Gallagher et al, 1973; Keenan et al, 2004; Weitzman et al, 1971) and in larger mammals such as horse (Cudd et al, 1995; Keenan et al, 2009) and sheep (Engler et al, 1989) have shown that plasma ACTH levels in basal conditions vary in a pulsatile manner. Similarly, the increases in circulating ACTH during stress are transient (Sarabdjitsingh et al, 2010).…”