In vitro study of acetylcholine and histamine induced contractions in colon and rectum of adult and neonate rats.

Contractile mechanisms of different parts of the gut in adult and neonate may not be identical due to developmental processes. The present study was undertaken to investigate acetylcholine (ACh) and histamine induced contractile responses of colon and rectum in adult and neonatal albino rats. Contractile responses were recorded from isolated in vitro preparations. The dose-response curve for ACh (0.001-100 microM) revealed dose dependent increase in contractile responses. A significantly (P < 0.05) greater contractile responses (g/g wet tissue) was observed in rectum as compared to colon. Atropine pretreatment significantly blocked ACh responses in both rectum and colon. The blockade was higher in adult preparations. The dose-response study for histamine (0.001-100 microM) did not show any significant difference between rectum and colon. Histamine (100 microM) induced contractions were significantly (P < 0.05) increased after pretreatment with pheniramine (100 microM) in adult rectum. This potentiating response of pheniramine was absent in neonate rectum. Such effect was also not seen in colon of both adult and neonate. The present investigation indicates that the contractile responses induced by ACh are similar in both adult and neonate, excepting that the blocking effect of atropine in colon was more pronounced in adult as compared to neonate. Further, the results also indicated different mechanism of histamine action in adults and neonates as evidenced by the significant enhancement of contractions by pheniramine only in adult rectum. Therefore, the present results indicate the existence of a different cholinergic and histaminergic activity in adult and neonate as well as in rectal and colonic tissue.