IMMUNOHISTOCHEMICAL LOCALIZATION OF 2 TYPES OF FATTY-ACID-BINDING PROTEINS IN RAT OVARIES DURING POSTNATAL-DEVELOPMENT AND IN IMMATURE RAT OVARIES TREATED WITH GONADOTROPINS

Background: The ovary of adult rats expresses two types of cytoplasmic fatty acid binding proteins (FABP), i.e., heart FABP (H-FABP) and int estinal 15 kDa protein (I-15P). We studied immunohistochemically the c ellular localizations of these FABPs in the ovaries of rats at various postnatal ages and in the ovaries of immature (3-week-old) rats treat ed with pregnant mare serum gonadotropin (PMSG) and human chorionic go nadotropin (HCG). Methods: The cryosections of ovaries were incubated with polyclonal antibodies against H-FABP and I-15P, and the immunorea ctions were visualized at both light and electron microscopic levels. Results: The immunoreactivity for H-FABP occurred temporarily in the f ollicular epithelial (granulosa) cells from 3 days to 2 weeks post par tum, and then was localized exclusively to the theca/interstitial glan d cells from 2 weeks to adulthood. In contrast, the immunoreactivity f or I-15P appeared temporarily in a small subset of theca/interstitial gland cells from 2 to 3 weeks, disappeared at 4 weeks, and was localiz ed exclusively to the corpus luteum cells after the onset of ovulation in the animal around 5 weeks. In the immature rat ovaries induced to ovulate by treatment with gonadotropins, I-15P-inmunoreactive cells we re first recognized in the luteinized granulosa layer of large preovul atory follicles, and increased in number progressively in the developi ng corpora lutea after the ovulation. Conclusions: Two types of FABPs are expressed in distinct steroid-producing cell types of rat ovary, a nd their expressions seem to be regulated in coincidence with the expr essions of respective steroid hormones. These results suggest that FAB Ps play specific roles in the ovarian hormone synthesis. (C) 1995 Wile y-Liss, Inc.