Effects of norepinephrine on cyclic nucleotide levels in the ductus deferens of the rat

Abstract

The effect of l-norepinephrine on cyclic nucleotide levels was studied in rat ductus deferens. Norepinephrine (0.01–0.3 m M) increased cyclic AMP and cyclic GMP levels in a concentration-dependent manner. Cyclic GMP was increased by about two-fold and cyclic AMP by 30%–40% by 0.1 m M norepinephrine after 3 min. Phenylephrine (0.1 m M) increased cyclic GMP levels about twofold without affecting cyclic AMP. Cyclic GMP was maximally increased by norepinephrine or phenylephrine after 3–10 min, but was not significantly changed after 20 sec, when contraction was fully developed. Atropine did not affect the norepinephrine-induced changes in cyclic nucleotide levels; phentolamine blocked the effect of norepinephrine on cyclic GMP, and propanolol blocked that on cyclic AMP. These findings indicate that in the ductus deferens α-adrenergic receptors are involved in the effect of catecholamines on cyclic GMP, and β-adrenergic receptors are involved in the effect on cyclic AMP levels. The presence of Ca 2+ was required for the effect of norepinephrine on cyclic GMP, but not on cyclic AMP.