Seasonal changes in luteal progesterone concentration and mRNA expressions of progesterone synthesis-related proteins in the corpus luteum of mares.

The study explores how seasonal changes impact the concentration of the hormone ‘progesterone’ (P₄) and progesterone synthesis-related proteins in the corpus luteum (CL) organ in female horses. It found that progesterone synthesis in the CL is influenced by seasonal fluctuations in the expression of related proteins.

Research Context

• The main focus is on progesterone (P₄), a crucial hormone involved in the reproductive cycle of females. However, in the context of this study, P₄ is looked at in connection with seasonal changes.
• Scientists are particularly interested in the corpus luteum (CL), an organ in the ovaries that plays a primary role in the production and regulation of progesterone.
• Little was known about how the proteins related to P₄ synthesis in the CL can be affected by seasonal changes, prompting this research.

Research Method

• A total of 74 ovaries containing a CL were collected from Anglo-Norman mares at different periods over a year in Kumamoto, Japan.
• These CLs were classified by stage (early, mid and regressed) based on a macroscopic observation of the CL and its related follicles.
• The mid CL, with the highest P₄ concentration, was the core subject. The researchers evaluated their seasonal changes.

Research Findings

• Luteal P₄ concentration and mRNA expression of the luteinizing hormone receptor (LHCGR) were at their lowest during the beginning of winter, and at their highest towards the end of winter.
• Moreover, mRNA expressions of proteins related to progesterone synthesis, such as the steroidogenic acute regulatory protein (StAR), P450 cholesterol side-chain cleavage enzyme (P450scc), and 3β-HSD, were at a minimum in the early winter and increased towards late winter.
• Therefore, the research concluded that P₄ synthesis in the CL correlates with seasonal fluctuations in the mRNA expressions of related proteins.