Mechanisms of diethylstilbestrol-induced relaxation in rat aorta smooth muscle

Abstract

The mechanisms of diethylstilbestrol (1 to 30 μM)-induced relaxation on noradrenaline (30 nM)-raised tone in the rat aorta smooth muscle were studied. Neither the increase of calcium content in the medium (3, 6 and 9 mM) nor Bay K 8644 (3, 10 and 100 nM) reversed diethylstilbestrol relaxation. Tamoxifen (3 μM), the quaternary derivate (tamoxifen ethyl bromide, 3 μM), actinomycin D (30 μM), cycloheximide (100 μM), Rp-cAMPS (30 μM), TPCK (1 μM) and difluoromethylornithine (1 mM) inhibited diethylstilbestrol-induced relaxation. Incubation with 2 μg/ml pertussis toxin, propranolol (1 μM), H-7 (10 μM), 2′,3′- and 2′,5′-dideoxiadenosine (10 and 30 μM, respectively) and methylene blue (10 μM) did not modify diethylstilbestrol-induced relaxation. Our results showed that presumably an activation of membrane mechanisms, protein kinase A activation, genomic mechanisms and polyamine synthesis might participate in diethylstilbestrol-elicited relaxation in addition to the increase in K ATP permeability, as previously described. Actinomycin D produces a synergistic effect, with tamoxifen, difluoromethylornithine and glibenclamide antagonizing the effect of diethylstilbestrol. In the case of the association of actinomycin D and glibenclamide, the antagonism of relaxation is complete. The fact that tamoxifen- and difluoromethylornithine-dependent mechanisms participate in diethylstilbestrol relaxation inhibited by glibenclamide suggests that two transduction pathways are involved in the relaxation. Therefore, K ATP channels and genomic mechanisms, both modulated by cyclic AMP (cAMP)-dependent mechanisms, are associated with diethylstilbestrol relaxation.