Autoradiographic visualization of alpha 1-adrenergic receptors in cervix of early pregnant rat.

alpha 1-Adrenergic receptors were identified, characterized, and localized in rat cervix on Day 6 of pregnancy by autoradiography. Autoradiographic study was performed in slide-mounted rat cervix sections using [3H]-prazosin ([3H]-PRAZ) as ligand. Binding was time dependent and specific. Pharmacological study indicated that specific [3H]-PRAZ binding was inhibited with high affinity by prazosin and phenylephrine and low affinity by yohimbine and clonidine. In cervix, the alpha 1-adrenergic receptors were localized mainly to the inner circular layer of the myometrium. Binding to the outer longitudinal layer of myometrium was moderate, and binding was absent in the endometrium. The regional distribution of alpha 1-adrenergic receptors strongly suggests that the circular layer of myometrium may function as an important modulator of contractile response of the cervix, probably involved in the retention of blastocysts at the utero-cervical end of the horn.