Blood pressures and penile muscle activity in the stallion during coitus.

BECKETT,S.D., R. S. HUDSON, II. F. WALKER, T.M. REYNOLDS, AND R. 1. VACHON. Blood pressure and penib muscle activity in the stallion during coitus. Am. J. Physiol. 225(5): 1072-1075. 1973.Electromyographic (EMG) electrodes were implanted in the ischiocavernosus (IC) and bulbocavernosus (BC) muscles of the Shetland stallion to monitor muscle activity. A needle-tipped polyvinyl catheter or subminiature pressure transducer \vas implanted in the corpus cavernosum penis (CCP) to determine the pressure during coitus. Results from the needle-tipped catheter show that the mean CCP pressure during the quiescent state of the penis was 13 mm Hg, increasing to 107 mm Hg when a receptive mare was brought into view. During coitus, mean peak CCP pressure was 3,998 mm Hg. Higher mean peak CCP pressures were recorded from the subminiature transducers with a mean of 6,530 mm Hg. The lower peak CCP pressures obtained from the catheter were because of the viscous forces associated with the small diameter of the catheter, and the elasticity of the polyvinyl dampened the frequency response so that the maximum peak pressure was not recorded. Correlation of the EMG activity with the peak CCP pressures indicates that the IC muscles were the source of energy for the extremely high pressures. This was further substantiated by the fact that anesthesia of the IC muscles with lidoCaine greatly reduced the CCP pressures of the stallions during attempted coitus.