Domestic animal endocrinology1991; 8(3); 353-368; doi: 10.1016/0739-7240(91)90003-3

Gonadotropin releasing hormone (GnRH) induced luteinizing hormone (LH) secretion from perifused equine pituitaries.

Pinaud, MA
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Roser, JF
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Dybdal, N

Abstract: In vitro responsiveness of the horse anterior pituitary (AP) gonadotropes to single and multiple GnRH challenges was examined. The pituitaries were collected from reproductively sound mares in estrus (n = 5) and diestrus (n = 5). Uniform 0.5 mm AP slices were subdivided using a 3 mm biopsy punch and then bisected for use in the perifusion chamber. Four bisected sections per chamber were perifused at 0.5 ml/min at 37 C for 560 min in Medium 199 saturated with 95% 0(2)/5% CO2. Ten minute fractions were collected after an initial 2 hr equilibration period. Four different treatment regimes of GnRH (10(-10) M) were evaluated: (A) three consecutive 10 min GnRH pulses separated by 80 and 100 min, respectively; (B) a single 120 min GnRH infusion; (C) a 10 min GnRH pulse followed 80 min later by a 120 min GnRH infusion and (D) two 10 min GnRH pulses separated by 60 min followed 80 min later by a 120 min GnRH infusion. Estimated total pituitary LH content was higher in estrous than diestrus mares (p less than 0.05). The total amount of LH released in response to GnRH tended to be greater in estrus than diestrus (p less than 0.1), whereas the percentage of LH released in estrus and diestrus was similar. An increase in the area under the LH response curve was noted with each successive 10 min pulse of GnRH during both estrus and diestrus (p less than 0.05), demonstrating a self-priming effect of GnRH. In addition, a significant increase in the peak LH amplitude (p less than 0.05) and the slope to peak amplitude (p less than 0.05) were observed for the 120 min GnRH pulse in regime C and D indicating that prior exposure to short-term pulses of GnRH increased the acute LH secretory response. These results suggest that in the cycling mare (1) the responsiveness of the pituitary (amount of LH released as percent of total LH) is similar in both estrus and diestrus, however, the magnitude of the LH response (total microgram amount of LH released) differs with the stage of the estrous cycle, being highest in estrus, and appears to be related, in part, to pituitary LH content and (2) GnRH self-priming occurs independently of the stage of the estrous cycle. Furthermore, we have demonstrated that the pulsatile mode of GnRH can act directly on the anterior pituitary to dictate the pulsatile release pattern of LH in the cycling mare.

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Publication Date: 1991-07-01 PubMed ID: 1747998DOI: 10.1016/0739-7240(91)90003-3Google Scholar: Lookup

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This study investigates the responsiveness of horse anterior pituitary gonadotropes to the Gonadotropin-releasing hormone (GnRH). It reveals that exposure to short-term pulses of GnRH increases the acute Luteinizing hormone (LH) secretion, and the LH response differs with the stage of the estrous cycle, with the highest response in estrus.

Gonadotropin-Releasing Hormone (GnRH) Challenges

The research scrutinized the response of horse anterior pituitary (AP) gonadotropes to single and multiple GnRH challenges. The examinations were conducted in vitro.
The pituitaries were taken from reproductively healthy mares in both estrus and diestrus states. Estrus refers to the period in the sexual cycle of female animals when they can conceive, whereas diestrus is the period of sexual inactivity after estrus.
Then, uniform 0.5 mm AP slices were subdivided using a 3 mm biopsy punch and bisected for use in the perifusion chamber.
The perifusion was conducted in a solution, at a constant temperature of 37 C, and with a specific mix of gases.

Research Method and Outcomes

Four different treatment regimes of GnRH were evaluated. These included three consecutive 10 minute GnRH pulses separated by 80 and 100 minutes respectively; a single 120 minute GnRH infusion; a 10 minute GnRH pulse followed 80 minutes later by a 120 minute GnRH infusion; and two 10 minute GnRH pulses separated by 60 minutes followed 80 minutes later by a 120 minute GnRH infusion.
It was observed that the total pituitary LH content was higher in estrous mares than in diestrus mares. The amount of LH released in response to GnRH also seemed greater in estrus than in diestrus mares.
A noticeable increase in the area under the LH response curve was seen with each successive 10 minute pulse of GnRH during both stages. This showed a self-priming effect of GnRH.
A significant increase in the peak LH amplitude was also observed for the 120-minute GnRH pulse in regime C and D. This indicates that prior exposure to short-term pulses of GnRH increases the acute LH secretory response.

Conclusion

The study concluded that the responsiveness of the pituitary (measured as the amount of LH released as a percent of total LH) is similar in both estrus and diestrus stages. However, the magnitude of the LH response, which is the total microgram amount of LH released, differs with the stage of the estrous cycle and is highest in the estrus stage.
The study’s findings suggest that GnRH self-priming occurs independently of the stage of the estrous cycle, and the pulsatile mode of GnRH can act directly on the anterior pituitary to influence the pulsatile release pattern of LH.

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Pinaud MA, Roser JF, Dybdal N. (1991). Gonadotropin releasing hormone (GnRH) induced luteinizing hormone (LH) secretion from perifused equine pituitaries. Domest Anim Endocrinol, 8(3), 353-368. https://doi.org/10.1016/0739-7240(91)90003-3