THYROTROPIN-RELEASING-HORMONE (TRH) AND CNS REGULATION OF ANORECTAL MOTILITY IN THE RAT

The effect of thyrotropin-releasing hormone (TRH) upon anorectal motil ity was investigated in acute male rat preparations. Micromolar doses of TRH were intrathecally (i.t.) infused at the L6 spinal level at a r ate of 1 mu l/min over 8 min. TRH infusions in 1.0-1000 mu M concentra tions elicited biphasic, dose-dependent anorectal contractions as meas ured by a rectal manometer. The 100 mu M dose yielded the most signifi cant increase in contractions over the greatest period of time. Atropi ne, administered as a pretreatment (100 mu g s.c.), blocked contractio ns normally produced by i.t. infusion of TRH (1000 mu M). Intravenous infusions of atropine (10 mu g) through a jugular catheter immediately blocked anorectal contractions produced by i.t. infusion of 100 mu M TRH, Sectioning of the hypogastric nerve, which supplies sympathetic i nnervation to the colon and internal anal sphincter, did not significa ntly affect contractions induced by 100 mu M TRH applied intrathecally . Disruption of the major pelvic ganglion fibers, however, completely abolished the contractions induced by 100 mu M TRH, either through the interruption of preganglionic parasympathetic fibers in the pelvic ne rve, or by disrupting postganglionic fibers. These findings extend the role of TRH in the regulation of defecatory behaviors.