Autoradiographic localization of [3H]RU 486 and [3H]progesterone in the uterus, pituitary and hypothalamus of the rat

Twenty-one castrated oestrogen-primed Wistar rats, which were2-months-old, were injected via the jugular vein with 100 µCi/100g body weight of [³H]RU 486 or [³H] progesterone. Some of thesereceived unlabelled compounds for competition studies. Samplesof reproductive tract, pituitary and hypothalamus were excisedafter 15 min. The 4-µm frozen sections were processedfor thaw-mounted autoradiography. The exposure time of the autoradiogramwas {small tilde}6 months. After the injection of [³H]RU 486and [³H]progesterone, the nuclear concentration of radioactivitywas most distinct in muscular and stromal cells of the uterus,and the epithelial nuclei of lumina and glands showed weak labelling.Nuclear localization was also observed in muscle cells of thevagina, cervix and oviduct. After injection of [³H]progesterone,the radioactivity was found in the nuclei and cytoplasm of anteriorpituitary cells and some cells showed a preferential nuclearconcentration of radioactivity. The distribution of [³H]RU 486in the anterior pituitary was more extensive than that of [³H]progesterone.In the hypothalamus, specific localization of [³H]RU 486 and[³H]progesterone existed in neurones accumulated in the preopticnucleus, preoptic suprachiasmatic nucleus and the periventricularnucleus. No localization was found in the diaphragm. Pretreatmentwith RU 486, but not with dexamethasone, reduced the nuclearconcentration of radioactivity of [³H]progesterone in the vagina,uterus, oviduct, pituitary and hypothalamus. The nuclear concentrationof radioactivity after injection of [³H]RU 486 was also decreasedby preinjection with progesterone. The autoradiographic resultssuggest that RU 486 and progesterone competed for the specificbinding site (possibly a progesterone receptor) in the targetcells at the levels of the uterus, pituitary and hypothalamusin vivo.