Potentiation by treatment with reserpine of α2-adrenoceptor-mediated contractions of rat tail artery

Abstract

The effects of a treatment with reserpine on α-adrenoceptor-mediated contractile responses of rat tail arteries were investigated in vitro. The potency of norepinephrine was slightly increased in arteries obtained from rats treated with reserpine. There was no significant change in the sensitivity of the arteries to serotonin, KCl and selective α 1-adrenoceptor agonists (methoxamine and phenylephrine). However, the potency of clonidine and UK-14,304, both selective α 2-adrenoceptor agonists, was greatly increased. UK-14,304-induced contractions of the arteries from rats treated with reserpine were inhibited strongly by rauwolscine, a selective α 2-adrenoceptor antagonist, but only slightly by corynanthine, a selective α 1-adrenoceptor antagonist. The contractions caused by re-introduction of Ca 2+ during exposure to UK-14,304 but not to methoxamine in a Ca 2+-free medium were potentiated by treatment with reserpine. Bay K 8644, an agonist of Ca 2+ channels, produced a concentration-dependent contraction only in the arteries from rats treated with reserpine. These result suggest that treatment with reserpine potentials α 2- but not α 1-adrenoceptor-mediated responses in rat tail arteries and that the potential could be related to changes in mechanisms linked to Ca 2+ influx.