Original article Immunocytochemical localization of atrial natriuretic factor (ANF) in rat female reproductive tract: evidence for a potential hormonal regulation A. Russinova a, *, M. Mourdjeva b , C. Valkova c , S. Kyurkchiev b , I. Kehayov b a Institute of Experimental Morphology and Anthropology, Bulgarian Academy of Sciences, Bonchev Str., Bl. 25, 1113 Sofia, Bulgaria b Institute of Biology and Immunology of Reproduction, Bulgarian Academy of Sciences, 73, Tzarigradsko shosse, 1113 Sofia, Bulgaria c Institute of Molecular Biology, BulgarianAcademy of Sciences, G. Bonchev Str., Bl. 25, 1113 Sofia, Bulgaria Received 12 April 2001; accepted 14 November 2001 Abstract In the present studies atrial natriuretic factor (ANF) was characterized immunocytochemically in the reproductive tract of immature female rats, and changes of ANF levels in response to different hormonal conditions were demonstrated. Administration of pregnant mare serum gonadotropin (PMSG) to immature animals has shown to be a useful method to synchronize growth, differentiation and atresia of ovarian follicles. ANF immunoreactivity was investigated in rat uterus and oviduct during follicular growth and estrogenic dominance (48 h after PMSG treatment) and during follicular atresia and progesterone dominance (96 h after PMSG treatment). Our immunocytochemical results showed that in rat uterus ANF was localized in endometrial mucosal and glandular epithelium and smooth muscle cells of the myometrium. In the oviduct ANF immunoreactivity was observed in mucosal cells and muscle layers. Immunocytochemical staining patterns and Western blot analysis revealed that ANF levels in rat uterus and oviduct are modulated by the hormonal status. ANF immunoreactivity was elevated during estrogenic dominance (48 h after PMSG) in uterus and oviduct. However, during progesterone dominance (96 h after PMSG) elevation of ANF immunoreactivity was observed in the uterus only. These results raise the possibility that ANF expression in rat oviduct is positively controlled by estrogen and negatively by progesterone. ANF staining in uterus during progesterone phase provides evidence that both estrogen and progesterone regulate ANF levels in uterus. The observed staining patterns indicate that ANF may have intracellular functions as well as a role in priming the extracellular environment. Accordingly, the possibility that ANF might be an important regulatory molecule for autocrine / paracrine communication within the female reproductive tract should be considered. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. Keywords: Immunocytochemistry; Oviduct; Rat; Uterus 1. Introduction Atrial natriuretic factor (ANF) is synthesized in atrial cardiocytes but it has also been found in a variety of others tissues. ANF stimulates the membrane-bound form of gua- nylate cyclase and inhibits adenylate cyclase (Hamet et al., 1984; Inagami et al., 1989); thereby it increases the accu- mulation of intracellular cyclic guanosine monophosphate (cGMP) and decreases cyclic adenosine monophosphate (cAMP) levels. ANF receptors designated guanylyl cyclase-A (GC-A) (Chinkers et al., 1989) were identified in various tissues and organs including the rat ovary (Gut- kowska et al, 1993). Recent studies have demonstrated that the ovarian ANF system is under gonadotropin regulation (Gutkowska et al., 1999; Acosta et al., 2000). The presence of messenger RNA coding GC-A receptor was shown in rat endometrium (Potvin and Varma, 1990), myometrial smooth muscle layers and endometrial uterine glands (Reis et al, 1995). Expression of biologically active ANF recep- tors was established in human uterus during pregnancy (Itoh et al., 1994), and ANF binding was demonstrated in human endometrial stromal cells (Gililland et al., 1992). Thus the uterus appears a target of ANF where the latter induces its biological effects through cGMP production. Moreover, Reis et al. (1997) demonstrated that ANF content follows a * Corresponding author. E-mail address: russinova@dir.bg (A. Russinova). Biology of the Cell 94 (2002) 91–98 www.elsevier.com/locate/biocell © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. PII: S 0 2 4 8 - 4 9 0 0 ( 0 1 ) 0 1 1 7 6 - 5