Characterization of adrenoceptor mechanisms in isolated guinea-pig uterine arteries

The adrenoceptors of the guinea-pig uterine artery were characterized pharmacologically. Circular segments of the artery, approximately 2 mm long, and with an external diameter of 250 micron, were mounted in miniaturized tissue baths. Noradrenaline, methoxamine and phenylephrine (concentrations ranging from 10 nM to 1 mM), in the presence of propranolol (0.1 microM) and cocaine (1 microM), induced concentration-dependent contractions of the arterial segments. Clonidine (10 nM to 0.1 mM) was less effective in producing contraction of the vessel. Prazosin (10 nM to 1 microM) antagonized noradrenaline-induced contractions; its pA2 was 7.68. Rauwolscine (10 nM to 1 microM) had no effect on noradrenaline-induced contractions. Isoprenaline (10 nM to 0.1 mM) in the presence of prazosin (1 microM) and cocaine (1 microM) had no relaxant effect on arteries contracted submaximally by prostaglandin F2 alpha (5 microM). Cocaine or normetanephrine treatment did not influence the noradrenaline-induced contractions. It is concluded that in guinea-pig uterine arteries, amine-induced contractions are mediated predominantly by alpha 1-adrenoceptors and that in this arterial preparation, relaxant beta-adrenoceptor effects and neuronal or extraneuronal uptake are of minor if any importance.