Alpha adrenergic receptors mediate angiotensin-induced prostaglandin production in the rabbit isolated vas deferens

The effect of alpha adrenergic receptor antagonists on concentration-dependent response to angiotensins II and III was examined in the electrically stimulated isolated rabbit vas deferens. The force generated by a nonadrenergic neural mechanism was reduced by both peptides whereas the force generated by adrenergic neural mechanisms was enhanced. Angiotensin III-induced inhibition of the nonadrenergic contraction was significantly greater than that of angiotensin II for all groups. Yohimbine (1 x 10^-4 M), an alpha-2 receptor antagonist, attenuated the depression of the nonadrenergic contraction produced by angiotensins II and III. Yohimbine (1 x 10^-5 and 1 x 10^-4 M) also significantly reduced angiotensin II-induced prostaglandin E (PGE) synthesis. Yohimbine only significantly altered the angiotensin III-induced PGE synthesis at an antagonist concentration of 1 x 10^-4 M. Rauwolscine (1 x 10^-8 and 1 x 10^-7 M) attenuated angiotensin II-induced PGE production and at a higher concentration (1 x 10^-6 M) reduced angiotensin III-induced PGE production. The alpha-1 antagonist, prazosin (1 x 10^-6 M), did not alter nonadrenergic contractile or PGE responses to either angiotensin. The alpha-2 agonist, clonidine, both inhibited the nonadrenergic neural contraction and enhanced PGE synthesis. We interpret these data to indicate that angiotensins II and III may act via separate mechanisms to induce PGE synthesis in the vas deferens, with angiotensin II effects being more dependent on norepinephrine release from adrenergic nerves.