Polymeric Immunoglobulin a Receptor in the Rodent Female Reproductive Tract: Influence of Estradiol in the Vagina and Differential Expression of Messenger Ribonucleic Acid during Estrous Cycle1

Previously we have shown that estradiol and progesterone regulate the levels of secretory component, the external domain of polymeric immunoglobin A (IgA) receptor responsible for transporting IgA from tissues into secretions, at both the mRNA and protein levels in the rodent uterus. In the present study, experiments were designed to determine whether polymeric immunoglobulin receptor (pIgR) is synthesized locally in the vagina and whether it is under the control of estradiol and progesterone. Polymeric IgR message corresponding in size to that previously reported in the liver and uterus was detected by Northern blot analysis of total RNA from the vagina. Levels of pIgR mRNA and pIgR in the vagina were found to vary with the stage of the cycle. Polymeric IgR mRNA levels were elevated at diestrus, reduced at estrus, and undetectable at proestrus. Immunohistochemical analysis of pIgR in the vagina indicated that the expression of protein correlated with the mRNA levels. When ovariectomized rats were treated with estradiol, progesterone, or a combination of the two for 3 days, pIgR mRNA levels were significantly reduced in estradiol-treated animals relative to saline-treated controls. No significant changes were observed in the pIgR mRNA levels of animals treated with progesterone alone or with a combination of estradiol and progesterone. Polymeric IgR expression analyzed by immunohistochemical staining correlated well with variations in mRNA levels seen following hormone treatment. In situ hybridization localized pIgR in uterine and vaginal epithelial cells. In the uterus, pIgR message was abundant in luminal and glandular epithelial cells at estrus and low at diestrus. In contrast, expression of pIgR mRNA was pronounced in vaginal epithelial cells at diestrus, while very little message could be localized in the epithelium at estrus. These findings demonstrate that pIgR is synthesized locally in the uterus and vagina and is under tissue-specific hormone regulation.