Effects of dihydrotestosterone administration with and without estradiol pretreatment on gonadotropin secretion in ovariectomized pony mares.

This research explores the impact of different hormone treatments on Gonadotropin secretion in ovariectomized pony mares. The main finding is that estradiol benzoate, dihydrotestosterone propionate and testosterone propionate influence the secretion of follicle stimulating hormone and luteinizing hormone.

Introduction and Objectives

• The study was aimed at investigating the effects of dihydrotestosterone propionate (DHTP) when administered alone or in combination with estradiol benzoate (EB) on follicle stimulating hormone (FSH) and luteinizing hormone (LH) secretion.
• This research compared the effects of these compounds to known effects of testosterone propionate (TP).

Methodology

• The research involved twenty ovariectomized pony mares. Mares were initially administered Gonadotropin releasing hormone (GnRH) to evaluate their baseline LH and FSH response.
• Subsequent treatments were created by dividing the mares into five groups. Two groups were given EB, two were given a vehicle (safflower oil), and a fifth group was given TP. These treatments were administered daily for 10 days.
• Following these treatments, a second injection of GnRH was administered. Next, DHTP was administered daily for 10 days to one group of EB-treated mares and one group of safflower oil-treated mares.
• The remaining EB- and oil-treated mares were administered more oil, and TP treated mares continued receiving TP.
• At the end of the treatment period, all mares were given a final GnRH injection.

Outcome

• The treatment of mares with EB statistically significantly increased LH concentrations in daily blood samples and amplified the LH response to administered GnRH.
• Administration of TP or DHTP resulted in reduced daily LH concentrations and the LH response to exogenous GnRH.
• The daily FSH concentrations were significantly reduced and FSH response to exogenous GnRH was significantly increased by treatment with EB alone, DHTP alone, or TP.

Summary of Findings

• The results indicate that DHTP, when administered alone or in conjunction with EB, influences the secretion of FSH and LH in a similar way to the administration of TP.
• Additionally, EB alone significantly impacts the secretion of these hormones. Therefore, these substances can effectively influence the hormonal balance in ovariectomized pony mares.