Inhibition of the soluble form of testis adenylate cyclase by catechol estrogens and other catechols.
The soluble form of rat germ cell adenylate cyclase was inhibited by compounds with a catechol moiety. Among the naturally occurring catechols tested, catechol estrogens were the most potent inhibitors. Catechol estrogens at 2-6 microM inhibited enzyme activity by 50% and almost completely at 30-100 microM concentration. The inhibitory activity of catechol estrogens depends on the catechol moiety of the molecule. Catechol per se also inhibited the activity of this enzyme, 50% inhibition being achieved at about 11 microM. The two hydroxyls of the catechol moiety are essential for the inhibitory interaction with the enzyme. Thus, aromatic compounds containing only one hydroxyl group in the benzene ring, such as tyrosine, phenylephrine, estradiol, and 6 alpha-hydroxyestradiol were either completely inactive or had marginal inhibitory activity at concentrations up to 0.3-1 mM. Moreover, methylation of the hydroxyl groups of the catechol moiety of the catechol estrogens as in 2-methoxyestradiol 3-methyl ether rendered the catechol estrogens inactive. The inhibitory potency of these compounds varied greatly depending on the structure associated with the catechol ring. Thus, compounds in which catechol is associated with an aliphatic side chain, such as dopamine, L-dopa, norepinephrine, and isoproterenol, were about 11- to 34-fold less potent than catechol. On the other hand, compounds in which catechol is associated either with a hydroaromatic ring system, as in apomorphine, or with an alicyclic ring system, as in catechol estrogens, were about 2- to 5-fold more potent than catechol. The inhibitory effect of dopamine, apomorphine, and catechol estrogens was not affected by specific D-1 or D-2 antagonist, indicating that they do not act via receptors for dopamine.