SUMMARY

KENAKIN, T. P., AND D. A. CooK. The effect of desensitization on the antagonism of the histamine response by phenoxybenzamine. Mol. Pharmacol. 17: 309-313 (1980). Blockade of the histamine response by phenoxybenzamine was studied in both desensi-tized and nondesensitized preparations of the longitudinal smooth muscle of the guinea pig ileum. It was found that desensitization to histamine had little effect on the parallel shift in the dose-response curve to histamine produced by phenoxybenzamine but did affect the antagonism of the maximum histamine response by this agent. Since there is evidence that this antagonist interacts at the receptor, these results suggest that desen-sitization of the histamine H1 receptor in this preparation involves changes at the receptor level, possibly alterations in conformation. The results are described in terms of the cyclic model of desensitization proposed by Katz and Thesleff and the “metaphiic effect” described by Rang and Ritter