Sex steroids influence LH-RH-receptor interaction

Area of Science:

• Endocrinology
• Reproductive Biology
• Neuroendocrinology

Background:

• Gonadotropin (LH and FSH) release is regulated by the hypothalamic hormone LH-RH.
• Sex steroids play a crucial role in modulating reproductive functions.
• The precise mechanisms by which sex steroids affect LH-RH action at the pituitary level require further elucidation.

Purpose of the Study:

• To investigate the in vitro effects of sex steroids on LH-RH-induced luteinizing hormone (LH) and follicle-stimulating hormone (FSH) release from rat anterior pituitaries.
• To examine the impact of orchidectomy and subsequent steroid treatment on pituitary responsiveness to LH-RH.
• To explore the role of pituitary plasma membrane binding sites for LH-RH in mediating steroid hormone effects.

Main Methods:

• Intact and orchidectomized male rats, and ovariectomized female rats were pretreated with testosterone propionate (TP) and/or estradiol benzoate (EB).
• Anterior pituitary glands were incubated in vitro with LH-RH to measure LH and FSH release.
• [125I] LH-RH binding assays were performed on pituitary plasma membrane fractions.

Main Results:

• Estradiol benzoate (EB) and a combination of EB plus testosterone propionate (TP) inhibited LH-RH-stimulated FSH release at higher doses.
• EB and EB plus TP stimulated LH release in intact rats, while inhibiting LH-RH-induced LH release in orchidectomized rats.
• Orchidectomy led to the loss of a low-affinity LH-RH binding site, which could be regenerated by TP treatment.

Conclusions:

• Sex steroids modulate LH-RH-induced gonadotropin release directly at the pituitary plasma membrane level.
• A single hypothalamic hormone (LH-RH) can specifically control the release of both LH and FSH.
• The regulatory mechanisms governing LH-RH-induced gonadotropin release differ between male and female rats.