Gonadotropin secretion and pituitary responsiveness to GnRH in mares with granulosa-theca cell tumor.

The research explores the hormonal changes and pituitary response to Gonadotropin-Releasing Hormone (GnRH) in horses with granulosa-theca cell tumors (GTCTs) before and after tumor removal. The study’s primary focus was to understand the influence of GTCTs on pituitary responsiveness and sex hormone metabolism.

Research Objectives

• Examine the blood concentration of inhibit, gonadotropins, and sex steroids in mares with GTCTs.
• Analyze the pituitary gonadotroph cells’ response to GnRH stimulus both before and after GTCT removal.

Methodology

• Eight mares with GTCTs were selected.
• Four of these mares, some in vernal transition period and others in the breeding season, were kept as control participants.
• Every mare was given a single dose of 40 micrograms of GnRH agonist through an intravenous injection.
• Blood samples were withdrawn every 15 minutes, two hours before and four hours after the injection.
• In four mares with GTCTs, the procedure was repeated 20 and 90 days following tumor removal.
• All plasma samples were analyzed for concentrations of ir-INH, LH, FSH, estradiol-17beta (E2), testosterone, and progesterone.

Key Findings

• E2 levels were substantially lower in mares with GTCTs when compared to control animals, both before and after surgery.
• Progesterone and testosterone concentrations showed no significant difference between the groups.
• Levels of ir-INH were found to be higher in GTCT mares before surgery than in control mares, which decreased to undetectable levels after tumor removal.
• Baseline Follicle-stimulating hormone (FSH) did not vary between control and GTCT animals before or after the ovaries were removed.
• Luteinizing hormone (LH) baseline values seemed to be higher for the affected mares, but not to a significant degree.
• Maximum release (MR) and area under the gonadotropin release curve (AUC) after the GnRH challenge for both gonadotropins were found to be similar between the groups.

In summary, the study indicates a significant influence of GTCTs on the balance of sex hormones and pituitary responses in mares. Further research may be needed to understand the clinical and long-term implications of these findings.