Increase in plasma progestagen concentrations in the mare after foetal injection with CRH, ACTH or betamethasone in late gestation.

The research article discusses how the injection of CRH, ACTH or betamethasone into a foetus can cause an increase in the maternal plasma progestagen concentrations in mares during late gestation.

Objective and Methodology

• The research was aimed at investigating the effects of the administration of CRH, ACTH or betamethasone to the foetus on maternal plasma progestagen concentrations from about 250 to 320 days of gestation.
• The case study used 16 healthy pony mares, their foetuses were injected using aseptic techniques. For controls, water or normal saline was used.

Measurements and Results

• Maternal plasma progestagen concentrations were measured using a commercial radioimmunoassay progesterone kit and confirmed using gas chromatography-mass spectrometry.
• The results clearly demonstrated that there was a significant increase in the mother’s progestagen concentrations after the foetus was injected with any of ACTH, CRH or betamethasone, regardless of the gestational age.
• Such increased concentration was not observed in the control subjects where normal saline or water was used as the injection fluid.

Outcome and Conclusions

• Out of the 16 mares that received a foetal injection, 13 gave birth to viable foals at gestational ages ranging from 307 to 339 days, while 3 delivered non-viable foals at 284 to 306 days gestation.
• The results of this study suggest that the rise in progestagens in horse mares just before giving birth is likely due to the activity of the foetal adrenal cortex.