Gonadotropin secretion and pituitary responsiveness to GnRH in mares with granulosa-theca cell tumor.
Abstract: Granulosa-theca cell tumors (GTCTs) are able to secrete variable amounts of sex steroids and immunoreactive inhibin (ir-INH). Although the pituitary appears to be affected by the presence of a GTCT, pituitary responsiveness to exogenous GnRH has not been examined. The aims of the present study were to: (i) assess the plasma hormone concentrations of ir-INH, gonadotropins and sex steroids in eight mares with GTCT and (ii) assess the responsiveness of pituitary gonadotroph cells to exogenous GnRH stimulus both before and after tumor removal. In seven mares, the contralateral ovary was firm, small and inactive. Histopathological observations of the tumors confirmed the presumptive diagnosis of a GTCT. Four mares, judged to be in vernal transition period (n=2) and in the breeding season (n=2), were used as controls. A single intravenous injection of 40 microg of GnRH agonist was given to each mare and blood samples were collected every 15 min from 2 h before to 4 h after injection. In four GTCT mares, this procedure was repeated 20 (n=2) and 90 (n=2) days after tumors removal. All plasma samples were analyzed for concentrations of ir-INH, LH, FSH, estradiol-17beta (E2), testosterone (T) by RIA and progesterone (P) by EIA. Results showed that E2 levels were significantly higher (P<0.001) in control animals compared to E2 levels in GTCT mares before and after surgery. P and T concentrations were not statistically different between the groups. Baseline levels of ir-INH were greater (P<0.05) in GTCT mares before surgery than in control mares, and decreased to undetectable levels after neoplasia ablation. Baseline FSH did not differ between control and GTCT animals either before or after the ovaries were removed. LH baseline values appeared to be higher for affected mares, but the difference was not statistically significant. Maximum release (MR) and area under the gonadotrophin release curve (AUC) after the GnRH challenge for both the gonadotrophins were similar between the groups.
Publication Date: 2006-05-02 PubMed ID: 16647750DOI: 10.1016/j.theriogenology.2006.03.030Google Scholar: Lookup
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Summary
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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.
Cite This Article
APA
Zelli R, Sylla L, Monaci M, Stradaioli G, Sibley LE, Roser JF, Munro C, Liu IK.
(2006).
Gonadotropin secretion and pituitary responsiveness to GnRH in mares with granulosa-theca cell tumor.
Theriogenology, 66(5), 1210-1218.
https://doi.org/10.1016/j.theriogenology.2006.03.030 Publication
Researcher Affiliations
- Department of Pathology, Diagnostic and Veterinary Clinic, Faculty of Veterinary Medicine, via S. Costanzo 4, 06126 Perugia, Italy. zelli@unipg.it
MeSH Terms
- Animals
- Estradiol / blood
- Female
- Follicle Stimulating Hormone / blood
- Gonadotropin-Releasing Hormone / pharmacology
- Gonadotropins / metabolism
- Granulosa Cell Tumor / metabolism
- Granulosa Cell Tumor / surgery
- Granulosa Cell Tumor / veterinary
- Horse Diseases / metabolism
- Horse Diseases / surgery
- Horses
- Inhibins / blood
- Luteinizing Hormone / blood
- Ovarian Neoplasms / metabolism
- Ovarian Neoplasms / surgery
- Ovarian Neoplasms / veterinary
- Progesterone / blood
- Testosterone / blood
- Thecoma / metabolism
- Thecoma / surgery
- Thecoma / veterinary
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