Straining-cremasteric reflex: identification of a new reflex and its role during increased intra-abdominal pressure.

The cremasteric muscle (CM) being composed of fleshy muscle bundles constitutes the active component of the fasciomuscular tube of the spermatic cord. On contraction, the CM compresses the cord veins pushing the blood in the pampiniform plexus to the abdominal veins. The role of the CM during increased intra-abdominal pressure (IAP) could not be traced in the literature. We investigated the hypothesis that the CM contracts upon IAP increase so as to support the cord veins and prevent abdominal veins reflux into them. Thirty-two healthy male volunteers (mean age 40.2 +/- 11.2 SD years) were studied. The IAP was recorded by a manometric catheter introduced into the rectum. The CM response to straining (sudden by coughing and slow by Valsalva's maneuver) was registered by a needle electrode introduced into the muscle. The response was recorded again after individual anesthetization of the CM and rectum. The test was repeated using saline instead of lidocaine and was performed on both sides. Straining (sudden or slow sustained) effected increase of the rectal pressure and CM EMG. The more the rectal pressure was increased by straining, the more the CM EMG was increased. The CM EMG response disappeared after prolonged or repeated successive straining. The CM did not respond to straining after individual anesthetization of the rectum and CM but did respond to saline administration. The response was similar from muscles on both sides. Increased CM EMG on straining postulates a reflex relationship which we call the 'straining-cremasteric reflex' (SCR). We suggest that this reflex, which results in CM contraction, supports the spermatic cord veins against the increase of the IAP induced by straining and against the tendency of venous reflux from the abdominal veins. The SCR may prove of diagnostic significance in neurogenic disorders provided further studies are performed in this respect.