MODULATION OF GUT SUBSTANCE-P AFTER WHOLE-BODY IRRADIATION - A NEW PATHOLOGICAL FEATURE

Exposure to ionizing radiation induces gastrointestinal dysfunction an d inflammatory reactions. The present study carried out in the rat, fo cuses on substance P, an inflammatory mediator implicated in the contr ol of intestinal motility. We have investigated the effects of gamma i rradiation on plasma and tissue substance P levels, ileal smooth muscl e activity, and properties of specific receptors, Plasma and ileal (mu cosa and muscle) substance P concentrations were measured by radioimmu noassay. At doses ranging from 1 to 8 Gy, plasma substance P levels in creased in a dose-dependent manner up to four days after irradiation. Ileal mucosal concentration decreased rapidly 1 hr after a 6-Gy irradi ation as compared to controls. A second class of binding sites appeare d three days after 6 Gy irradiation, In addition, substance P contract ile effects measured on isolated ileum showed a fourfold decrease of E C(50), three days after 6 Gy irradiation. These results indicated that gamma irradiation induced an increase of plasma levels concomitant wi th a modification of gastrointestinal substance P specific binding sit es and contractile activity.