The influence of subacute dyflos administration on the sensitivity to agonists of longitudinal and circular muscle preparations of the guinea-pig ileum.

1. Changes in the EC50 values to various agonists in longitudinal and circular muscle preparations of guinea-pig ileum were investigated following daily pretreatment of the animals for 10 days with dyflos (1.2 mg/kg, s.c.). 2. In the longitudinal muscle no significant change in sensitivity to acetylcholine and potassium chloride was noted following dyflos treatment. Marked subsensitivity to carbachol and histamine was observed. 3. In circular muscle a marked supersensitivity to acetylcholine occurred and there was no change in sensitivity to carbachol. 4. Dyflos treatment induced an increase in the slope of the log concentration-response curve and the maximal contractile response obtained to agonists in both longitudinal and circular muscle preparations. An increase in tissue mass was also associated with dyflos pretreatment. 5. Subsensitivity development was not attributable to changes in affinity for agonists at the receptor site but rather to changes at the post-receptor level leading to a nonspecific subsensitivity.