Abstract
The effects of histamine on contraction of rabbit taenia coli were studied. The results obtained were as follows: 1) The contractile response to histamine was appeared at the concentration of $10^{-7}M$ and increased in a dose-dependent manner to the concentration of $10^{-4}M$. 2) The magnitude of the histamine-induced contractile response was declined during short-term exposure in rabbit taenia coli. After 40-min exposure to histamine, the contractile response did not altered. 3) Histamine-induced contraction was not influenced by hexamethonium$(10^{-4}M)$, propranolol$(10^{-4}M)$ and phenoxybenzamine$(10^{-6}M)$. 4) $H_1-receptor$ blockade such as chlorpheniramine$(10^{-6}M)$ and pyrilamine$(10^{-6}M)$ completely abolished the response of the taenia coli to exogenous histamine, while $H_2-receptor$ blockade (cimetidine, $10^{-6}M$) did not alter. 5) After the treatment of verapamil the histamine-induced contraction was significantly inhibited, but in the treatment of 2 mM $La^{3+}$ it was not influenced. 6) In the absence of $Ca^{2+}$, histamine induced contraction in the different manner of acetylcholine. When taenia coli war treated with atropine$(10^{-6}M)$ which was completely blocked the contraction by acetylcholine$(10^{-4}M)$, histamine-induced contraction was not altered. These results suggest that in the rabbit taenia coli exogenous histamine induced contraction through $H_1$-receptor, but not through the mechanism of acetylcholine.