Dimethylphenylpiperazinium antigen peptide iodide, N methylserotonin hydrochloride, 5,6 dihydroxyserotonin, 5,7 dihydroxyserotonin, N methyltryptamine hydrochloride, N,N dimethyltryptamine hydrochloride and 5 methoxygramine hydrochloride were obtained from Alrich Chemical Co. . SubstancePwas obtained from Bachem Chemicals. Angiotensin II was a generous gift from Ciba Geigy. Prostaglandin Docetaxel solubility was a gift from Dr. T. Elizabeth. Pike from Upjohn Chemical Co.. Quipazine maleate was a generous gift from Miles Laboratories. All inorganic salts were analytical grade purchased from Mallinckrodt. Diphenhydramine was purchased from Parke and Davis as a 10 mg/ml ampule. The effective use of 5 HT to ileum pieces or the longitudinal muscle myenteric plexus planning, induced a dose dependent muscle contraction accompanied by a rest to standard anxiety. The magnitude of the muscular contraction was proportional to the concentration of 5 HT. Enough time for the contraction to achieve basal tension was inversely related to the amount, the best concentration of 5 HT developed the fastest fade to standard tension. Four min after pretreatment with a dose of 5 HT, a second dose triggered a low contractile response. For an illustration fig is seen by of this phenomenon. 1. A priming dose of 4. 3 X 10M 5 HT displaced the dose effect curve to the right in a similar manner without greatly Cholangiocarcinoma affecting the maximal response. The blocking effectation of 5 HT was fully reversible upon washing. The response curve was shifted even further by higher priming doses of 5 HT of 5 HT to the right, decreasing to a small extent the maximal response achieved. A priming dose of 4. 3 X10 M 5 HT entirely antagonized the contractile ramifications of 5 HT, as evidenced by way of a smooth doseresponse curve. After steady tissue washing, recovery of the 5 HT priming dose response in this case was almost complete in about 30 min. Analysis of section of this information in a plot exposed a straight line. The pA2 price for the 5 HT~5 HT relationship was 6. 57 _ 0. 41 and the slope of the line was 1. 59. The pA2 pA10 value was 0. 60. The 5 HT pD2 value established in the same preparation was 6. 52 _ 0. 46. 5 HT in the longitudinal muscle of the ileumexhibitedasimilarauto inhibition result as that observed in the whole ileum. Application of a dose of 4. 3 X 10 M 5 HT produced a 55 fold increase in the 5 HT Emaxso,, Consistently with the results obtained in the entire ileum, a dose of 4. 3 X10 Mcompletelyabolished5 HT reactions in nine preparations studied. The 5 HT induced auto blockade was particular to serotonergic drugs. 4. 3 X 10 M 5 HT.