1The effects of temperature on the time course of desensitization induced by acetylcholine and histamine, and on the recovery from desensitization were studied in the longitudinal muscle of the guinea-pig ileum.2 Self-and cross-desensitization produced by acetylcholine (10-M) occurred rapidly in the first 1Omin of exposure to the agonist, with the same time course and the same degree of desensitization over the temperature range of 1 C to 31°C. 3 Self-desensitization produced by histamine (10 5M) also occurred rapidly in the first 10min of exposure to the agonist, and showed great temperature-dependence, especially at 1 C and 21°C, but scarcely occurred at 6°C. 4 Cross-desensitization produced by histamine developed gradually with time and showed a moderate temperature-dependence between 1 C and 31°C, but scarcely occurred at 6°C. 5 The recovery processes from desensitization showed marked temperature-dependence. Recovery was halted completely at 1 1C. 6 These studies suggest that acetylcholine-induced desensitization may be attributed to a single nonspecific mechanism. Histamine-induced desensitization may be due to at least two mechanisms: it occurs in both a specific and non-specific manner. Each of these desensitizations can be characterized by its unique temperature-dependence.

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