Microvascularization and angiogenic activity of equine corpora lutea throughout the estrous cycle.

This research investigated the growth, microvascular development, and endocrine function of the corpus luteum—an important structure in the reproductive system of mares—throughout the estrous cycle. Prostaglandin F2alpha, a hormone typically associated with reproductive activity, was found to likely play a role in the regression of blood vessel growth in the corpus luteum in the later stages of the estrous cycle.

Objectives and Methodology of the Research

• The study set out to examine three major aspects concerning the growth and activity of the corpus luteum in horses. The researchers observed the tissue growth and microvascular development of this reproductive structure throughout the estrous cycle. They also tested the in vitro angiogenic activity (formation of new blood vessels) from various luteal tissues in response to luteotrophic hormones such as luteinizing hormone and prostaglandin E2, and luteolytic hormones such as prostaglandin F2alpha. Lastly, they tried to correlate the observed data with the endocrine function of the luteum corpus.
• For the investigation, luteal tissue samples were taken from different stages of the luteal phase and were then cultured with no hormone, or with prostaglandin F2alpha, luteinizing hormone, prostaglandin E2, LH + PGE2 or LH + PGF2alpha. The resultant culture media, conditioned by the equine luteal tissue, were used to stimulate the growth of bovine aortic endothelial cells (BAEC). This was done to assess the presence of angiogenic activity in the equine luteal tissue.

Findings of the Research

• Microvascular density, or the degree of blood vessel formation, increased during the early and mid-luteal phases. After reaching a peak, it began declining during the late luteal phase, and decreased further in the corpus albicans—a degenerated form of the corpus luteum.
• The hyperplasia or proliferation of luteal tissue also peaked during the mid-luteal phase, followed by tissue regression.
• The media conditioned by the equine luteal tissue were found to stimulate the mitogenesis or cell division of BAEC, suggesting the presence of angiogenic activity in the luteal tissue.
• A significant observation was that media conditioned by late-luteal phase tissue in presence of prostaglandin F2alpha lead to a considerable reduction in BAEC cell division. This indicates that prostaglandin F2alpha might play a role in vascular regression in the corpus luteum during the late luteal phase.

Implications of the Research

• The study’s results indicate that angiogenesis (blood vessel formation) and vascular regression in the mare’s corpus luteum throughout the estrous cycle might be coordinated with the development of non-vascular tissue.
• Furthermore, the findings propose that these processes might be regulated by a variety of factors, including hormones such as prostaglandin F2alpha. This can open new lines of research in equine reproduction, with potential implications in managing fertility, diagnosis, and treatment of reproductive disorders.