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

A needle-tipped catheter or subminiature pressure transducer was implanted in the corpus spongiosum penis (CSP) of Shetland Pony stallions to determine pressure during coitus. Electrodes for monitoring the electromyographic (EMG) activity were implanted in the ischiocavernosus (IC) and bulbospongiosus (BS) muscles. The mean peak CSP pressure recorded with the catheter was 762 mm of Hg, and with the subminiature pressure transducer, it was 994 mm of Hg. The simultaneous occurrence of the CSP pressure peaks and bursts of BS muscle activity indicated that these muscles were the likely source of energy for the increased pressures, which were far greater than the systemic blood pressure. This conclusion was further supported by the finding that anesthesia of the BS muscles greatly reduced the CSP pressures of the stallion during attempted coitus.