Effects of testosterone, dihydrotestosterone and estradiol on gonadotropin release after gonadotropin releasing hormone administration in cyclic mares.

The research article investigates how testosterone, dihydrotestosterone, and estradiol influence the release of gonadotropin in cyclic mares when administered with a gonadotropin releasing hormone. The key finding was that treatment with testosterone and dihydrotestosterone resulted in a higher response of follicle-stimulating hormone to the gonadotropin releasing hormone compared to other treatments.

Study Methodology

• The study was conducted on sixteen intact cyclic mares. The mares were treated on the fourth day of estrus and then every other day for a total of six injections.
• There were four different types of treatments. These include injections of testosterone propionate, dihydrotestosterone (DHT) benzoate, estradiol (E2) benzoate, and safflower oil.
• The mares were given GnRH on Day 3 of estrus (pretreatment) and again 24 hours after the last injection of steroid or oil.

Key Findings

• The study found that testosterone propionate treatment resulted in a greater follicle-stimulating hormone (FSH) response to the second injection of GnRH compared with all other treatments.
• DHT benzoate also triggered a greater FSH response to GnRH compared with control and E2 benzoate-treated mares.
• Testosterone propionate and E2 benzoate administration suppressed the normal diestrous rise in FSH concentrations exhibited by the control and DHT benzoate-treated mares.
• The study found that steroid treatment did not affect the luteinizing hormone (LH) response to GnRH. However, the testosterone propionate treatment did suppress concentrations of LH in daily blood samples during Days 3 to 6 of treatment.

Conclusions

• The research concludes that testosterone’s effect on FSH after GnRH treatment is due to two different properties of the hormone or its metabolites acting simultaneously.
• Testosterone increased the secretion of FSH in response to GnRH, an effect similar to DHT (an androgenic effect).
• At the same time, testosterone suppressed FSH concentrations in daily blood samples in a similar manner to E2 benzoate (an estrogenic effect).