Effects of p-chlorophenylalanine on the sensitivity of rat intestine to agonists and on intestinal 5-hydroxytryptamine levels during Nippostrongylus brasiliensis infection

Infection of rats with the nematode N. brasiliensis caused non-specific increases in maximum response of isolated intestine to acetylcholine and 5-hydroxytryptamine (5-HT), and a specific subsensitivity to 5-HT. Intestinal levels of 5-HT, measured fluorimetrically, increased approximately 2 fold during infection. Treatment of infected rats with parachlorophenylalanine (PCPA) depleted the gut of 5-HT, and prevented the specific subsensitivity to the amine but not the increases in maximum response. Depletion of intestinal 5-HT did not prevent the immune expulsion of the parasites. It is concluded that the specific subsensitivity of the gut is due to the elevated levels of 5-HT during infection, but that the increased maximum responses are due to some other factor. Further, the lack of effect of PCPA on parasite rejection casts doubt on the proposed role of 5-HT in this process.