Increased responsiveness of intestinal and vascular smooth muscle to agonists in rats infected with Nippostrongylus brasiliensis.

Rats were infected with the nematode parasite, N. brasiliensis. During infection, the responsiveness of intestinal and vascular smooth muscle to agonists changed. For example, the maximum response of isolated segments of intestine to acetylcholine were increased. In part, this enhanced responsiveness was due to hypertrophy of intestinal smooth muscle. In addition, there was an almost two-fold increase in the tension developed per unit of cross-sectional area, indicating that the contractile capacity of the muscle was also increased during infection. The responsiveness of vascular smooth muscle to agonists was also enhanced. In the perfused rat hindquarters, the maximum response to phenylephrine increased throughout infection, reaching a peak at a time (day 14 of infection) when the rate of worm expulsion was maximal. The possibility is considered that these changes in the responsiveness of intestinal and vascular smooth muscle are the result of an immune response.