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<sup>-7</sup>M and increased in a dose-dependent manner to the concentration of 10<sup>-4</sup>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<sup>-4</sup>M), propranolol(10<sup>-4</sup>M) and phenoxybenzamine(10<sup>-6</sup>M). 4) H<sub>1</sub>-receptor blockade such as chlorpheniramine(10<sup>-6</sup>M) and pyrilamine(10<sup>-6</sup>M) completely abolished the response of the taenia coli to exogenous histamine, while H<sub>2</sub>-receptor blockade (cimetidine, 10<sup>-6</sup>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<sup>3+</sup> it was not influenced. 6) In the absence of Ca<sup>2+</sup>, histamine induced contraction in the different manner of acetylcholine. When taenia coli war treated with atropine(10<sup>-6</sup>M) which was completely blocked the contraction by acetylcholine(10<sup>-4</sup>M), histamine-induced contraction was not altered. These results suggest that in the rabbit taenia coli exogenous histamine induced contraction through H<sub>1</sub>-receptor, but not through the mechanism of acetylcholine.
(0)
(0)