Relationship between the morphology of and progesterone production by the corpus luteum of the mare.

The research article focuses on the study of the histology of the corpus luteum of the mare during ovulation, specifically how its morphology correlates with progesterone production.

Objective Summary

The research analyzes the histological progression and progesterone production of the corpus luteum of a mare during ovulation and early pregnancy.

Details of Research

• The study involved thirty-five cycling and early pregnant mares with known breeding histories.
• The corpus luteum (CL), a temporary endocrine structure involved in ovulation and early pregnancy stages, was observed under light microscopy at different stages – growing, secreting, and regressing.
• Thecal cells, which are instrumental in hormone production, were found to be most developed a few days before ovulation. They degenerated quickly and within 24 hr after ovulation, all remaining thecal cells showed signs of advanced degeneration.
• Hypertrophy (increase in cell size) and luteinization (conversion into lutein, a hormone required for menstrual and pregnancy cycles) of the granulosa cells began 10 hr after ovulation.
• Maximum cell size (37-5 mum) was reached after granulosa cells started hypertrophying and luteinizing.
• The luteal tissue, part of the ovary that forms after releasing an egg, mainly expanded through hypertrophy of the lutein cells.

Types of Lutein Cells and Degeneration

• Two types of lutein cells were found in the CL – a large light-staining cell and a small dark-staining cell.
• For a non-pregnant mare, degeneration of the lutein cells would begin on Day 12 after ovulation. In a pregnant mare, the degeneration would start on Day 38 after ovulation.
• The primary CL of pregnancy regressed after the secondary CL formed.

Correlation with Progesterone

• The study concluded that the progesterone concentration in the peripheral plasma had a close correlation with the morphological changes occurring in the CL. This implies the structural changes in the CL during the menstrual and pregnancy cycles may influence progesterone production, a steroid hormone crucial for maintaining pregnancy.