POLYMERIC-IG RECEPTOR GENE-EXPRESSION IN RABBIT MAMMARY-GLAND DURING PREGNANCY AND LACTATION - EVOLUTION AND HORMONAL-REGULATION

The polymeric immunoglobulin receptor (poly Ig-R) mediates transcytosi s of IgA and IgM antibodies produced by local plasma cells across epit helial cells of mucosal and glandular tissues. Gene expression of the poly-Ig R was analyzed in rabbit mammary gland during pregnancy and la ctation. The poly Ig-R was expressed as early as day 8 (G8) of gestati on and mRNA accumulation remained low until about G18. From G21, the m RNA abundance increased and reached steady state levels similar to 5-f old higher at day 15 of lactation (L15) when compared to basal levels at G8. The hormonal regulation of poly-Ig receptor gene expression was assessed in mammary organ cultures. Poly-Ig R mRNA accumulation in ma mmary explants cultured for 24 or 48 h in the presence of ovine prolac tin (oPRL) was significantly increased to a maximal 4-fold level at 1 mu g ml(-1) of oPRL. Estradiol (100 pg ml(-1)) or progesterone (1 mu g ml(-1)) did not further stimulate poly-Ig R expression. In contrast, their combination resulted in a significant 30-50% decrease of poly-Ig -R mRNA levels. The addition of 1 mu g ml(-1) of cortisol to medium in the absence or presence of estradiol or progesterone decreased the am ount of poly-Ig-R mRNA. The results suggest that until mid-pregnancy, poly-Ig-R expression is inhibited by elevated progesterone-estradiol c oncentrations and that the subsequent increase is due to the concomita nt decrease of the two circulating steroids and the increase of serum prolactin levels.