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

This research focuses on the prenatal development and ultradian rhythms of hormones related to stress and immuno-responses (adrenocorticotropic hormone (ACTH) and cortisol) in late-gestation fetal horses. These were monitored for changes, and compared with levels in maternal and non-pregnant adult horses, to better understand their role in equine fetal development and childbirth.

Research Focus

The study’s objective was to shed light on the roles of the hypothalamic-pituitary-adrenal axis in the maturation and timing of childbirth in horses. More specifically, the focus lay on the following aspects:

• Investigating the changes in plasma levels of ACTH and cortisol in late-gestation fetal horses.
• Evaluating possible ultradian rhythmic release of these hormones in fetal horses.
• Comparing plasma hormone levels in fetuses to those in maternal and non-pregnant adult horses.

Methodology

Six late-gestation horse fetuses (between 278-304 days of gestation) were catheterized and sampled daily until delivery. The researchers tracked and analysed the changes in the plasma concentrations of the hormones and corticosteroid binding capacity.

Findings

ACTH and cortisol:

• ACTH concentrations increased significantly from 159 +/- 21 to 246 +/- 42 pg/ml in the last two days before delivery.
• Cortisol increased significantly from 3.1 +/- 1.0 to 13.4 +/- 3.7 ng/ml over the last nine days before delivery. The 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.

Corticosteroid binding capacity:

• The capacity for fetuses to bind corticosteroids decreased from 49.5 +/- 20.5 to 16.1 +/- 2.2 ng/ml over the last ten days before parturition.

The findings suggest that ACTH, cortisol, and corticosteroid binding capacity in fetal horses undergo significant changes towards the end of gestation, more specifically during the last 48 to 72 hours before delivery. This indicates that these hormones likely play a significant role in the onset of childbirth in horses.

Conclusion

Though this research makes important strides in understanding the endocrinology of equine fetuses, the specific roles of these hormones in fetal development and parturition timing remain unclear. Further studies considering a larger sample size and investigating other gland functions are recommended to corroborate and expand on these findings.