Prolactin, gonadotropin, and hair shedding responses to daily sulpiride administration in geldings in winter.

The research studied the effects of a dopamine antagonist, sulpiride, on the secretion of prolactin, gonadotropin and hair shedding in male horses during winter. It found that while sulpiride increased prolactin concentrations, its impact on gonadotropin secretion and hair shedding were minor and contrary to expectations.

Objective of the Study

• Researchers aimed to understand the effectiveness of daily subcutaneous injections of sulpiride, a dopamine antagonist, in increasing prolactin secretion in geldings (castrated male horses) during winter.
• They also sought to uncover if increased prolactin levels would speed up hair shedding or boost gonadotropin secretion.

Procedure

• The study involved five geldings, which each received daily injections of either sulpiride (100mg in vegetable oil) or only the vehicle (vegetable oil) from February 8 to March 29.
• Blood and hair samples from the subjects were collected on February 8, every seven days thereafter until March 29, and around the time of injections.
• All geldings were administered an injection of GnRH (Gonadotropin-releasing hormone) and thyrotropin-releasing hormone on March 30.

Findings

• The results showed that the prolactin response to sulpiride varied in a quadratic manner over the eight-week sampling period, indicating that the effect of the drug on prolactin levels was inconsistent.
• Prolactin concentrations in control geldings did not change after the injection and during the entire eight-week period
• The weight of hair pulled off from sulpiride-treated geldings did not peak to the same extent or as highly as that in control geldings, and remained a higher weight through week 11.
• Sulpiride administration also seemed to decrease the LH (Luteinizing hormone) response to GnRH, although this change was not deemed statistically significant (P=.071).
• The medication did not modify the FSH and prolactin responses to secretagogue (P>.25).

Conclusion

• The study concluded that even though sulpiride did succeed in increasing prolactin concentrations in geldings during winter, its effects on gonadotropin secretion and hair shedding were minor and contrary to predictions. This suggests that sulpiride action in geldings may not fully align with its expected physiological effects and needs further investigation.