Effect of glucocorticoids on alpha-2 adrenoceptors in vas deferens of reserpinized rat in organ culture.

The changes in alpha adrenoceptors in vasa deferentia of reserpinized rats in organ culture were examined by binding studies with 3H-clonidine, 3H-yohimbine and 3H-prazosin. On organ culture for 1 day, the 3H-clonidine binding sites decreased by 1.07 pmol/g tissue and after 2 days no binding sites were detectable. 3H-Yohimbine binding sites also decreased during culture, but in smaller extent than 3H-clonidine binding sites. On the other hand, 3H-prazosin binding sites showed no apparent change in amount during culture. Addition of 0.1 mM hydrocortisone or dexamethasone to the culture medium inhibited the decrease in 3H-clonidine binding sites (1.7 pmol/g tissue), and the effect of glucocorticoid was blocked by the inhibitors of protein synthesis, cycloheximide and puromycin. However, hydrocortisone showed no effect on the 3H-yohimbine and the 3H-prazosin binding sites. An anti-endocytotic agent, an anti-microtubular agent and protease inhibitors had no effects on the decrease of 3H-clonidine binding sites during culture. These results suggest that the amount of alpha-2 adrenoceptors can change rapidly while alpha-1 adrenoceptors are stable and that glucocorticoids are important in regulation of conformation of alpha-2 adrenoceptor through synthesis of certain protein(s).