Abstract:
Retinoid-binding proteins and nuclear receptors are expressed in thereproductive tissues of different species and their expression is hormonallyregulated. In the present study, we demonstrated immunocytochemically thetemporal and spatial localization of retinol-binding protein (RBP), cellularretinoic acid-binding protein I (CRABPI) and retinoid X receptor &bgr;(RXR&bgr;) in porcine ovary, oviduct and uterus during the oestrous cycle. RBPand CRABPI were localized in the cytoplasm, whereas RXR&bgr; occurred in thenucleus. RBP was not detected in either the ovary or the oviduct at any stageof the oestrous cycle. CRABPI was present in luteal cells of the ovary onlyduring dioestrus and in glandular and ciliated cells of the oviduct duringoestrus. In the ovary, RXR&bgr; was always present in granulosa cells andgerminal epithelium, with highest levels observed during oestrus. In theuterus, RXR&bgr; was present throughout the cycle in both the endometrium andthe myometrium. However, changes in RXR&bgr; were observed in the endometrium,with highest levels observed during dioestrus. RBP and CRABPI could beobserved in the endometrium only during dioestrus. The results show that theoccurrence of retinoid-binding proteins and nuclear receptors in individualtissues of the reproductive tract are strongly dependent on the stage of theoestrous cycle. In the oviduct, the expression of CRABPI seems to be dependenton oestrogen, whereas in the uterus the expression of RBP and CRABPI isinfluenced by progesterone. The association of expression in differentsections of the reproductive tissues investigated shows that the presence ofspecific proteins involved in retinoid metabolism was dependent on eventsassociated with ovulation, the migration of the oocyte through the oviduct andthe possible implantation of the blastocyst into the uterus.