Desensitization of beta receptor mediated cyclic AMP response of cultured fibroblasts by partial agonists

Two novel beta-adrenergic myocardial stimulants of general structure: Formula: (see text), where R is a phenyl or benzyl group were investigated for their ability to stimulate and desensitize the cyclic AMP response of C6 glioma cells. Compound ICI 89, 963 (R:phenyl) which elicited less than 1% of the maximum increase in cAMP produced by isoproterenol, was strikingly effective as a desensitizer of the isoproterenol response. This desensitization was markedly reduced by propranolol. Compound ICI 119,033 (R: benzyl) which was a more effective stimulant of cAMP synthesis than ICI 89,963, was also a more effective desensitizer of the isoproterenol response of C6 cells. The kinetics of the desensitization by ICI 89,963 were comparable with those for isoproterenol reaching a maximum in 2 to 3 hours. The data indicate that beta-adrenergic agonists are more potent as desensitizers of the cyclic AMP response than as stimulants of that response.