Oxytocin, vasopressin, prostaglandin F(2alpha), luteinizing hormone, testosterone, estrone sulfate, and cortisol plasma concentrations after sexual stimulation in stallions.

The research is about an experiment conducted on male horses to determine how sexual stimulation affects the plasma concentrations of various hormones and proteins. The study found that sexual activity increased the concentrations of some substances, while it had no effect on others.

Objective of the Research

The principal objective of the study was to determine the effects of sexual stimulation on the plasma levels of several hormones and proteins in male horses, specifically oxytocin (OT), vasopressin (VP), 15-ketodihydro-PGF(2alpha) (also known as the prostaglandin PG metabolite), luteinizing hormone (LH), testosterone (T), estrone sulfate (ES), and cortisol (C).

Methodology

• The experiment was conducted on 14 light horse stallions of proven fertility.
• Semen samples were collected using a Missouri model artificial vagina.
• Blood samples were collected at various intervals during and after sexual activity – specifically, 15, 12, 9, 6, and 3 minutes before exposure to an estrous mare, at erection, at ejaculation, and at 3, 6, and 9 minutes after ejaculation. Blood sampling continued every 10 minutes for an hour after ejaculation.

Findings

• The research found that sexual activity led to an increase in the plasma concentrations of oxytocin, vasopressin, cortisol, the prostaglandin metabolite, and estrone sulfate.
• However, there were no changes found in the levels of luteinizing hormone and testosterone.
• The study also identified a negative correlation between cortisol and vasopressin at erection, and between cortisol and testosterone before and at the time of erection. This suggests that cortisol may play an inhibitory role in the mechanism of sexual arousal, similar to that described for men.

Implications and Conclusion

Based on the results of the experiment, the researchers concluded that sexual stimulation can have varying impacts on the levels of certain hormones and proteins in the blood of male horses. While some substances increased in concentration, others remained unaffected. Notably, the observed negative correlations involving cortisol may suggest a potential inhibitory role for this hormone in the sexual arousal mechanism, resonating with what has been observed in human males. This finding can potentially shed light on the complex interplay of various substances during sexual activity in male horses, and by extension, in other mammals as well.