Estrogen and progesterone receptors in the endometrium, myometrium, and metrial gland of the rat during the decidualization process.

Uterine cytosolic and nuclear receptors for estradiol (E2) and progesterone (P), were simultaneously determined in pseudopregnant rats subjected to a traumatic decidualizing stimulus (knife-scratch). The entire decidualizing endometrium, myometrium, and metrial gland were separated, homogenized, and studied on alternate days beginning with day 1 post trauma (pt) and extending to day 13 pt when even the metrial gland is regressing. The rise and fall in E2 and P receptors during the earlier stages of deciduoma differentiation confirmed the work of others. Splitting of the deciduoma on day 5 pt into antimesometrial and mesometrial segments showed a higher concentration of cytosolic P receptor in the well differentiated antimesometrial segment, whereas there was a higher concentration of E2 cytosolic receptor in the still differentiating mesometrial segment. The differences, measured as femtomoles per microgram DNA or per mg protein were statistically significant. The receptor changes in the myometrium were not as pronounced as in the endometrium especially with regard to the low myometrial levels of nuclear E2 and P. The metrial gland which comes into prominence while the deciduoma is regressing, showed sustained high concentrations of cytosolic P receptor. It is suggested that although initiated by the same decidualizing stimulus, the hormonal and receptor interplay in the metrial gland may be somewhat different from that of the deciduoma. The metrial gland merits further study because of an implied immunological role.