Direct effects of free and conjugated steroids on GnRH stimulated LH release in cultured equine anterior pituitary cells.

This research study investigates the direct impact of free and conjugated steroids on the release of Luteinizing Hormone (LH) stimulated by Gonadotropin Releasing Hormone (GnRH) in cultured cells from the anterior part of the pituitary gland in horses.

Research Overview

• The study uses anterior pituitary cells from donor mares that were cultured using a specific medium and hormone-free horse serum.
• The cells were then treated with various concentrations of estrogen and incubated with or without GnRH.
• The media and cell extracts were then assessed for LH using a radioimmunoassay technique.

First Series of Experiments

• In the first set of experiments, pituitary cells were premixed with ethanol or varying concentrations of Estradiol (E2) before a 4-hour incubation period either with or without introducing GnRH.
• It was observed that E2 significantly enhanced the release of LH when prompted by GnRH, with the most powerful response observed at a specific concentration of E2.
• Furthermore, E2 dramatically boosted the pituitary’s reaction to varying concentrations of GnRH, reducing the minimum effective dose and augmenting the maximum response to GnRH.
• Interestingly, E2 had no effect on basal LH release.

Second Experiment

• In the second trial, the researchers evaluated the effects of multiple forms of estrogen – E2, Estrone (E1) and Estrone Sulfate (E1S) – on the basic and GnRH-incited LH discharge.
• While E1 increased GnRH-induced LH release, its maximum effective dose and ED50 were 100 times higher than what was observed for E2.
• Notably, E1S showed no estrogenic activity, even at concentrations as high as 100 nM.

In conclusion, this study provides insights into the role of different forms of estrogen in the stimulation of LH release by GnRH in equine anterior pituitary cells. This could potentially highlight key aspects in understanding how variations in hormone levels could affect this hormonal axis in horses.