Corpus spongiosum penis pressure and penile muscle activity in the stallion during coitus.

This research studied the pressures within a pony’s penis during intercourse and how it correlates with muscular activity, concluding that the penis’s large pressures are likely due to muscle contractions, specifically in the bulbospongiosus muscle.

Methodology and Procedures

• The researchers implanted a needle-tipped catheter or a subminiature pressure transducer into the corpus spongiosum penis (CSP) of Shetland Pony stallions. The CSP is a part of the penis responsible for its rigidity during an erection.
• They also implanted electrodes into two muscles: the ischiocavernosus (IC) and bulbospongiosus (BS), to monitor their electromyographic (EMG) activity. EMG measures the electrical activity produced by skeletal muscles.

Findings and Observations

• The mean peak CSP pressure recorded with the catheter reached 762 mm of Hg, and when measured with the subminiature pressure transducer, it reached 994 mm of Hg.
• The researchers noted that the peak pressures in the CSP occurred simultaneously with bursts of activity in the BS muscles, indicating a relationship between the two.

Conclusions

• The researchers concluded that the large pressures in the stallion’s penis during coitus are likely due to the activity of the BS muscles. This conclusion was drawn because the pressures recorded were significantly higher than the stallion’s systemic (overall) blood pressure, indicating that another force (in this case, muscle contractions) was contributing.
• This hypothesis was further supported when the researchers found that anesthetizing the BS muscles reduced the CSP pressures during attempted coitus, confirming the role these muscles play in maintaining penile pressures.