In-vitro and in-vivo responsiveness of the corpus luteum of the mare to gonadotrophin stimulation.

The research investigates the sensitivity of a horse’s corpus luteum to gonadotrophin stimulation, both in vitro and in vivo, with a focus on the hormones LH, hCG, and PMSG. The study found a noticeable increase in progesterone production when exposed to these hormones, particularly with hCG, but did not find changes in the anterior pituitary’s release of LH.

Objective and Methodology

• The research aimed to figure out how well horse corpus luteum responds to stimulation from certain gonadotrophins, both in a controlled laboratory setting (in vitro) and in a living mare (in vivo).
• Researchers used dispersed horse luteal cells for their in-vitro experiments. They studied the cells’ morphology to recognize two unique groups based on the cells’ sizes.
• Over a certain range of concentrations, they evaluated the cells’ response to horse LH, hCG, and PMSG, three types of gonadotrophins responsible for regulating processes in the reproductive system, including progesterone secretion.

Results

• Both horse LH and hCG notably stimulated progesterone production at all levels of treatment in suspended luteal cells. hCG in particular showed a significantly higher stimulation of progesterone secretion than horse LH.
• In the in-vivo study, mares were given an intramuscular injection of hCG over three days after oestrus. The result was a significant increase in peripheral progesterone concentrations that started on day seven and lasted until day fourteen.
• Even after oestrus, raised progesterone levels were maintained in mares that became pregnant after hCG treatment, suggesting an influence on early pregnancy.

Conclusions

• The researchers found that the mare’s corpus luteum responds to gonadotrophins, particularly hCG, both in vitro and in vivo.
• Despite this, hCG treatment did not appear to impact the release of LH from the anterior pituitary gland, suggesting the effect was specifically on progesterone production.
• Overall, the study provides new insights into how manipulation of gonadotrophin levels could potentially modulate progesterone levels and impact reproductive processes in mares, such as the oestrous cycle and early stages of pregnancy.