Effects of castration on alpha 1-adrenoceptor subtypes in the rat aorta

The expression of alpha 1-adrenoceptor subtypes in several tissues is regulated by gonadal hormones. In this study, we investigated whether castration regulates the alpha 1-adrenoceptor subtypes mediating the contractions of the aorta from male rats to noradrenaline. Noradrenaline induced similar concentration-dependent contractions in the aorta from control and castrated rats. Treatment of the aorta from both control and castrated rats with the alpha 1B/alpha 1D-adrenoceptor alkylating agent chloroethylclonidine resulted in approximately 1600-fold rightward shift in the concentration-response curves to noradrenaline. The pA2 values found for WB 4101, benoxathian (alpha 1A-selective) and BMY 7378 (alpha 1D-selective) indicate that alpha 1D-adrenoceptors are involved in the contractions of the aorta from control and castrated rats to noradrenaline. However, there was a 15-fold difference between the pKB estimated through the lowest effective concentrations of the alpha 1A-adrenoceptor selective antagonist 5-methyl-urapidil in the aorta from control and castrated rats. The pKB estimated in aorta from control rats is consistent with the interaction with alpha 1D-adrenoceptors (7.58 +/- 0.06), while that calculated in organs from control rats is consistent with alpha 1A-adrenoceptors (8.76 +/- 0.09). These results suggest that castration induces plasticity in the alpha 1-adrenoceptor subtypes involved in the contractions of the aorta to noradrenaline.