Studies on the mechanism of thyrotropin releasing hormone induced inhibition of gastrointestinal transit.

Intracerebral administration of thyrotropin releasing hormone (TRH) inhibited gastrointestinal transit in the mouse as determined by the charcoal meal test. A similar inhibitory effect was produced by morphine administered subcutaneously. TRH enhanced morphine-induced inhibition of gastrointestinal transit. Intracerebral injections of cyclo (His-Pro), a postulated metabolite, did not affect gastrointestinal transit either by itself or that produced by morphine. It is suggested that gastrointestinal transit effects of TRH are not mediated via its conversion to cyclo (His-Pro).