Expression of functional melatonin MT(1) receptors in equine luteal cells: in vitro effects of melatonin on progesterone secretion.

The research explores the molecular mechanisms through which melatonin influences the ovarian function in mares. Specifically, it investigates how melatonin affects progesterone secretion, primarily via its MT(1) receptors present in the mare’s ovarian cells.

Methods and Experimentation

• The study comprises two experiments, both using follicles and corpora lutea (CL) extracted from slaughterhouse ovaries.
• Experiment 1 primarily focuses on analyzing the presence of melatonin MT(1) receptor mRNA and protein in the follicles and CL.
• Experiment 2 involves culturing CL in a specific medium (Dulbecco’s modified Eagle’s medium-F12 medium) supplemented with equine chorionic gonadotrophin (eCG), melatonin in variable dosages, forskolin, and luzindole. The effects of these supplements on progesterone production and enzyme expression were evaluated.

Findings

• The research confirmed that MT(1) receptor mRNA and protein exist in the follicles and CL.
• The study demonstrated that melatonin decreases both eCG- and forskolin-stimulated production of progesterone in a dose-dependent manner.
• Additionally, melatonin was found to inhibit the forskolin-stimulated expression of cholesterol side-chain cleavage enzyme (P450scc), an enzyme that converts cholesterol into pregnenolone, a precursor of progesterone.
• Experiments showed that luzindole, an antagonist for melatonin MT(1) and MT(2) receptors, could neutralize the inhibitory effect of melatonin on progesterone production and enzyme expression.

Conclusions

• The research suggests the presence of responsive melatonin receptors in ovarian (luteal) cells and affirms that melatonin plays a role in regulating the endocrine function of the equine CL, particularly the secretion of progesterone.