Relationships among LH, FSH and prolactin secretion, storage and response to secretagogue and hypothalamic GnRH content in ovariectomized pony mares administered testosterone, dihydrostestosterone, estradiol, progesterone, dexamethasone or follicular fluid

Thirty-five ovariectomized pony mares were used to study the relationship among luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL) concentrations in blood (secretion), in pituitary (storage) and in blood after secretagogue administration, as well as the content of gonadotropin releasing hormone (GnRH) in hypothalamic areas, under various conditions of steroidal and nonsteroidal treatment. Five mares each were treated daily for 21 d with vegetable shortening (controls), testosterone (T), dihydrotestosterone (DHT), estradiol (E sub(2)), progesterone (P sub(4)), dexamethasone (DEX) or charcoal-stripped equine follicular fluid (FF). Secretagogue injections (GnRH and thyrotropin releasing hormone, TRH) were given one d prior to treatment and again after 15 d of treatment. Relative to controls, treatment with T, DHT and DEX reduced LH secretion, storage and response to exogenous GnRH, whereas treatment with E sub(2) increased these same characteristics. Treatment with P sub(4) reduced only LH secretion. Treatment with T, DHT, E sub(2) and DEX reduced FSH secretion, whereas treatment with P sub(4) increased it and had no effect. All treatments increased FSH storage, whereas only treatment with T and DHT increased the FSH response to exogenous GnRH.