In vivo induced desensitization of beta-adrenoceptors in rat lung. Effect of nitrendipine

The effect of nitrendipine on desensitization of beta-adrenoceptors induced by isoprenaline was investigated using rat lungs. Rats were treated with saline, isoprenaline, nitrendipine, or nitrendipine + isoprenaline. After 7 days of treatment, tracheas were isolated and the dissociation constant (Kb) for the propranolol-beta-receptor complex was determined. Lung parenchymal tissue was used to study the binding characteristics of beta-adrenoceptors. The Kb value for the propranolol-beta-receptor complex was found to be up to 6.4-fold higher in trachea isolated from isoprenaline-treated rats (32 +/- 5.4 nM) than from control rats (4.9 +/- 1.2 nM); the Kb value for trachea from isoprenaline + nitrendipine-treated rats was 7.0 +/- 1.2 nM. A 31% reduction in the number of beta-adrenoceptors as compared to those of the control group was observed in the isoprenaline-treated group while the number of the beta-adrenoceptors in the isoprenaline + nitrendipine-treated group was significantly increased as compared to that of the isoprenaline-treated group.