The human myometrium expresses multiple isoforms of the corticotropin-releasing hormone receptor.

Specific high affinity binding sites for CRH have been identified and characterized in the pituitary and central nervous system as well as in peripheral tissues. We recently identified and characterized a specific CRH receptor in human myometrium that changes to a high affinity state before term. In view of this, we searched for receptor heterogeneity in the pregnant and nonpregnant human myometrial CRH receptor. Myometrial membranes were prepared by differential centrifugation from either pregnant (cesarian section) or nonpregnant (hysterectomy) myometrium. Using a specific RRA followed by isoelectric focusing and autoradiography, multiple isoforms of the human myometrial CRH receptor were identified that were identical in both pregnant and nonpregnant myometrium. Five isoforms were identified (pI 4.65, 4.8, 4.95, 5.1, and 5.2). Reduction of disulfide bridges with reducing agents (dithiothreitol and cysteine) increased the specific binding of CRH to its myometrial receptor, and the action of dithiothreitol affected the two most basic receptor isoforms. These results suggest the presence of multiple isoforms of CRH receptors that may have different properties and functions and the presence of disulfide bridges within the myometrial CRH receptor, which are important, but not critical, for the receptor binding.