A difference in alpha-adrenoceptor mechanisms in vasa deferentia isolated from young and old rats

A difference in alpha-adrenoceptor mechanisms in vasa deferentia isolated from 3 weeks old and 40 weeks old rats were studied by analysis of the concentration-response curve of norepinephrine and Scatchard plot of specific [3H]-prazosin binding to microsomal fractions. The efficacy of norepinephrine and capacity of the maximum binding sites of [3H]-prazosin estimated in 40 weeks old rats were larger than those in the 3 weeks old rats, while there was no difference in the affinity of norepinephrine estimated in the 3 weeks old rats and in the 40 weeks old rats. The increase of efficacy for norepinephrine in the vas deferens from the 40 weeks old rats is due to the increase in the total concentration of alpha-adrenoceptors.