OBSERVATIONS ON THE SIGNIFICANCE OF 5-HYDROXYTRYPTAMINE IN RELATION TO THE PERISTALTIC REFLEX OF THE RAT.

Peristalsis of normal rats, and of rats fed either on a control diet or on a tryptophan-free diet (5-hydroxytryptamine-depleted rats), was studied in vitro and in situ to test the hypothesis that 5-hydroxytryptamine functions as a local hormone in the intestine and may be essential for initiation of the peristaltic reflex. A tryptophan-free diet depleted intestinal 5-hydroxytryptamine by a mean value of 90%; in some rats, the depletion appeared to be complete. Peristaltic responses, even of rats with complete depletion, were qualitatively similar to, and quantitatively not statistically different from those of normal or of pair-fed control animals whose intestinal mucosa contained high concentrations of 5-hydroxytryptamine. Intraluminal and serosal 5-hydroxytryptamine produced effects in 5-hydroxytryptamine-depleted rats similar to those in the normal and in the control animals. Furthermore, the maximal stimulatory effects of 5-hydroxytryptamine on peristaltic performance were not greater than spontaneous variations in performance in any group of animals, except with tryptophan-fed control rats, when the effects of the amine on peristalsis in situ were greater than spontaneous variation. It was therefore concluded that 5-hydroxytryptamine is not essential for peristalsis in the rat.