This study showed that when the rat lived in simulated altitude of 4000 m. the ?-receptor number in cerebral cortex increased first, then returned to normal gradually. The receptor number in rat lung reduced first. then rose high above the normal, and then dropped to normal. On the first day after the rats returned to normal atmosphere the ?-receptor number in both tissues increased moderately. No significant change of Kd values was observed in the experimental groups. The Hill numbers were around 1. The hydrocortisone, dexamethasone and betamethasone could increase ?-receptor number in both tissues of normal rats, and had the same effect on hypoxic rat cerebral cortex. The results mentioned above indicate that the three glucocorticoids can reverse the reduction of ?-receptor number in rat lung during the initial stage of hypoxla, which may lead part of the beneficial effect of glucocorticoids on high-altitude disease.

It is generally considered that the experiment of radioligand binding assay ( RBA) of receptors with frozen tissue sections is difficult. In this study the conditions involved in the RBA of ?-adre-nergic receptors with rat brain sections on the superior colliculus level was investigated. 3H-Dihydroalprenolol (3H-DHA), a ?-adrener-gic receptor antagonist, was used as the labeled ligand. The data obtained from this experment are as follows: Bmax=17.3?4.5fmol/mg of dry tissue, Kd=5.8?0.6nM, association rate constant=0.112?0.025 nM-1 ? min-1,dissociation rate constant=0.69?0.07min-1, the IC50 of propranolol=1.00?0.15?10-8M, IC50 of practolol=1.67?0.22?10-5M, IC50 of isopreterenol=1.32?0.31 ? 10-6M.These results are in agreement with those obtained from RBA with homogenate, which indicates that the frozen tissue sections are useful preparations in the RBA of ?-adrenergic receptors.