Blockade of histamine-induced contractions of guinea pig ileum by β-haloalkylamines

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Abstract
In the longitudinal muscle strip of guinea pig ileum phenoxybenzamine (POB) produces a maximum parallel shift of 0.7 log units in the dose–response curve to histamine. In the presence of sodium thiosulfate in the wash fluid the parallel shift with retention of maximum response increases to about 2 log units, and a similar value is obtained for N-ethyl-N-(2-bromoethyl)-1′-naphthylamine. The agent N-ethyl-N-(2-chloroethyl)benzylamine produces a significantly smaller shift of dose–response curve of 1.53 log units before the maximum response becomes depressed. The receptor-specific depression of maximum response produced by higher doses of POB is reversed by sodium thiosulfate and by bovine serum albumin, while the parallel shift in dose–response curve is unaffected by both treatments. These findings may be explained by a hypothesis involving interaction of 2-haloalkylamines at two sites.