IMMUNOCYTOCHEMICAL IDENTIFICATION OF BASIC FIBROBLAST GROWTH-FACTOR IN THE DEVELOPING RAT MAMMARY-GLAND - VARIATIONS IN LOCATION ARE DEPENDENT ON GLANDULAR STRUCTURE AND DIFFERENTIATION

We raised antiserum to human recombinant basic fibroblast growth facto r (rbFGF) in rabbits. With this affinity-purified antiserum, other ant isera to rbFGF and commercial antiserum to bovine pituitary bFGF, we u ndertook immunocytochemical detection of bFGF in histological sections of rat mammary glands at different developmental stages. In nongrowin g ducts, anti-bFGF serum stains the basement membrane/myoepithelial ce lls, whereas in serial sections most of this stain is observed to be a ssociated with anti-laminin-staining basement membranes rather than wi th anti-callus-keratin-staining myoepithelial cells. The weak staining of the myoepithelial cells is enhanced when NiCl2 is included in the detection system, but little staining for bFGF is observed in the epit helial cells. In growing neonatal ducts from 1-day-old rats, in growin g terminal end buds (TEBs) and, to a lesser extent, in growing alveola r buds (ABs) in prepubescent (21-day) and pubescent (50-day) rats, bot h their inner and outer cells are stained moderately by anti-bFGF sera . In nongrowing ducts from rats aged 6 days, in non-growing ABs of rat s aged 60 days and more, and in alveoli from pregnant and lactating ra ts, only the basement membrane/myoepithelial cell area is stained by a nti-bFGF sera; the epithelial cells are unstained. Staining of the myo epithelial cells is enhanced by mixtures of rbFGF and anti-bFGF sera i n nongrowing ducts, but there is little change in the staining of grow ing TEBs. All staining by anti-bFGF sera is abolished with heparin in the reactions. We suggest that the immunoreactive bFGF is present main ly bound to heparan sulfate glycosaminoglycans in the basement membran e of resting structures, but that immunoreactive bFGF becomes associat ed with proliferating cells, particularly those intermediate in charac teristics between epithelial and myoepithelial cells in growing struct ures such as TEBs.