Influence of oestradiol on alpha 2-adrenoceptor binding sites on intact platelets of young male volunteers

The specific binding (Bmax) of (3H-methyl)yohimbine to alpha 2-adrenoceptor binding sites on intact platelets was increased by 43% in 6 out of 7 young male volunteers 4 days after a single i.m. injection of 10 mg sustained release oestradiol, and it had returned to the starting value 4 weeks after drug administration. Mean plasma oestradiol was 331 pg/ml on Day 4 and it was within the pre-treatment control range of 19 pg/ml 4 weeks after the injection. A close correlation between the post-injection plasma oestradiol concentration and the increase in alpha 2-adrenoceptor binding sites on intact platelets was not found.