CELLULAR PROLIFERATION AND FIBROBLAST GROWTH-FACTORS IN THE CORPUS-LUTEUM DURING EARLY-PREGNANCY IN EWES

To determine the relationship between cellular proliferation and the p resence of FGF-1 and FGF-2 in the ovine corpus luteum (CL) during earl y pregnancy, ewes received an intravenous injection of bromodeoxyuridi ne (BrdU) 1 h before slaughter (n = 3/day) on day 12 after estrus (non pregnant) or on days 12, 18, 24 or 30 after mating (pregnant). The lab eling index (LI; number of BrdU-labeled nuclei expressed as a percenta ge of total nuclei) of each CL was determined by immunohistochemistry and subsequent image analysis. FGF-1 and FGF-2 were immunolocalized by using specific antibodies, and indirect immunoperoxidase detection. M oreover, FGF-2 was immunolocalized by using a primary antibody and flu orescein isothiocyanate (FITC)-labeled secondary antibody, and immunof luorescence was quantified by using an interactive laser cytometer and image analysis. Results demonstrated that the LI was similar for CL o f nonpregnant and pregnant ewes on day 12 (4.27+/-0.23 vs 5.10+/-0.14% ) and decreased (P < 0.05) from days 12-30 of pregnancy (2.73+/-0.08, 2.02+/-0.09 and 1.70+/-0.04% on days 18, 24 and 30, respectively). FGF -1 was present in the cytoplasm of large and a few small parenchymal l uteal cells, and the distribution and intensity of staining was simila r for nonpregnant and pregnant ewes on day 12 as well as across days o f pregnancy. In contrast, FGF-2 immunoreactivity was present only in l uteal nonparenchymal cells and interstitial areas and was greater (P < 0.05) for pregnant than nonpregnant CL on day 12 (2.34+/-0.12 vs 0.14 +/-0.01%). Although FGF-2 immunoreactivity decreased (P < 0.01) from d ays 12-30 of pregnancy (0.70+/-0.04, 0.22+/-0.01 and 0.06+/-0.02% on d ays 18, 24, and 30, respectively), it was highly correlated (r = 0.99, P < 0.01) with luteal LT. We therefore suggest that FGF, and especial ly FGF-2, play a role in luteal cell proliferation or turnover during early pregnancy, and may thereby contribute to the maintenance of lute al function, which is critical for the successful establishment of pre gnancy.