Some pharmacological effects of p-chlorophenylalanine unrelated to tryptophan hydroxylase inhibition.

1 Experiments were performed on a variety of tissues from different species to establish whether or not the properties of p-chlorophenylalanine methyl ester (PCPA) included a 5-hydroxytryptamine (5-HT)-like action which might explain the soporific action of PCPA in chicks. 2 PCPA, like 5-HT, contracted the rat fundal preparation (as did PCPA base), and in cats enhanced twitch tension of a lower limb flexor reflex, evoked adrenal medullary secretion and attenuated histamine-induced gastric secretion; the effects on the rat fundal strip and the adrenal medulla were prevented by methysergide. 3 Like 5-HT, PCPA elicited bronchoconstriction of guinea-pig lungs, isolated or in vivo; this was not prevented by methysergide but reduced by polyphloretin and by indomethacin. Perfusate collected from the lungs during PCPA-induced bronchoconstriction and applied to superfused isolated tissues contained a substance with prostaglandin-like activity. 4 In contrast, the effect of PCPA on the guinea-pig isolated ileum differed from that of 5-HT, since it relaxed the ileum when contracted by transmural excitation, by acetylcholine, histamine of 5-HT and contracted the ileum on wash-out.