SENSITIVITY CHANGES IN THE ISOLATED ILEUM OF THE GUINEA PIG AFTER PRETREATMENT WITH RESERPINE

¹ Department of Pharmacology, West Virginia University Medical Center, Morgantown, West Virginia

Reserpine (1.0 mg/kg) administered i.p. for 5 to 7 days increased the sensitivity of the isolated ileum to 5-HT, nicotine and 1, 1-dimethyl-4-phenylpiperazinium iodide but not to acetylcholine, histamine or potassium. The same schedule of pretreatment produced 95% depletion of the norepinephrine content of the ileum and more than doubled the acetylcholine content. Chronic pretreatment with reserpine did not alter the amount of radioactivity present in the tissue after 1- and 5-min incubation periods with either C¹⁴-5-HT or H³-histamine. One dose of reserpine (1.0 mg/kg, 24 hr before the experiment) did not alter the sensitivity of the isolated ileum to 5-HT. It is concluded that the supersensitivity produced by reserpine in this preparation is a result of its ability to increase the tissue content of acetylcholine. This type of supersensitivity is therefore specific for ganglion-stimulating agents and is different from the nonspecific supersensitivity produced by pretreatment with reserpine in the nictitating membrane of the spinal cat. The hypothesis that nonspecific supersensitivity results only from chronic inhibition of excitatory nerve pathways is supported.