Adrenoceptor Mechanisms in the Regulation of Contractile Activity in the Human Cervix

Abstract

The effects of adrenoceptor agonists and antagonists on the contractile activity of cervical strips from early pregnant and nonpregnant women were studied. Noradrenaline and the α-adrenoceptor agonist, phenylephrine, had a stimulatory effect on smooth muscle activity. This response could be blocked totally by the α-adrenoceptor antagonist, phenoxybenzamine. Isoprenaline, known to be a β-adrenoceptor agonist with some α-adrenoceptor activity, had stimulatory and inhibitory effects, whereas the β₂-adrenoceptor agonist, terbutaline, exhibited a pure inhibitory action. The inhibitory effects of isoprenaline and terbutaline were totally blocked by the β-adrenoceptor antagonist propranolol. In pregnant patients, the sensitivity to noradrenaline was significantly higher, and the inhibitory action of terbutaline was less pronounced, which indicated the predominance of α-receptor activity in the uterine cervix during pregnancy.