Immunohistochemical localization of the eosinophil major basic protein in the uterus horn and cervix of the rat at term and after parturition.

Distribution of the eosinophil major basic protein (MBP) was studied in the rat uterus horn and cervix by means of immunohistochemistry using an antiserum raised against rat MBP. Various hormonal contexts were investigated: pre- and post-parturition, the estrous cycle, and ovariectomy followed by hormonal treatment or without treatment. MBP was detectable in the cervix as early as 12 h post-partum, appearing in the stroma close to the myometrium. The MBP had spread throughout the stroma toward the luminal epithelium after a few days. In contrast, no MBP was seen in sections of the corresponding pre- and post-partum uteri and in the pre-partum cervix. In cycling rats, MBP was distributed equally in the cervix and uterus and was more abundant during proestrus and estrus. In ovariectomized rats subsequently treated with progesterone, no MBP was detected in the cervix or uterus. In the cervix of ovariectomized rats treated with estradiol, MBP first appeared in the muscle layer situated between the two cervical lumina and then reached the stroma; within a few days only the stroma was stained. Inversely, in the uterus MBP-staining first appeared in the stroma. In conclusion, analysis of the distribution of MBP in rat uterus revealed a marked difference in the response of the cervix and horn to a hormonal environment.