TRH and substance P independently affect gastric motility in nucleus raphe obscurus of the rat.

Abstract

The purpose of this study was to investigate whether there exists a functional interaction between thyrotropin-releasing hormone (TRH) and substance P (SP) in the nucleus raphe obscurus (NRO) in their effects on gastric motor function. This was accomplished by microinjection of TRH (6-45 pmol) and SP (10 and 135 pmol) into the NRO alone and then either as a mixture or in rapid sequential order in alpha-chloralose-anesthetized rats, while intragastric pressure and pyloric and greater curvature motility were monitored. TRH (15 and 45 pmol) evoked significant increases in gastric motor activity, whereas SP (135 pmol) elicited decreases in intragastric pressure. SP at a dose of 10 pmol was ineffective alone in altering gastric motor function. Microinjection of a mixture of TRH (15 pmol) and SP (10 pmol) into the NRO resulted in significant increases in intragastric pressure, pyloric motility, and greater curvature motility; these changes in gastric motor function were similar to the effect of TRH (15 pmol) alone. A mixture of TRH (15 pmol) and SP (135 pmol) resulted in changes in gastric motor activity that were significantly less than the effect of TRH (15 pmol) microinjected into the NRO alone and appeared to be an additive effect of each peptide. The results of sequential microinjections of both peptides were consistent with these findings. The stimulative effect of TRH (15 and 45 pmol) on intragastric pressure, microinjected into the NRO 30 s after SP (135 pmol), did not differ from the effect of TRH microinjected at the same doses after vehicle.(ABSTRACT TRUNCATED AT 250 WORDS)