Evidence for an Organ- and Sex-Specific Role of Basic Fibroblast Growth Factor in the Development of the Fetal Mammalian Reproductive Tract*

Basic fibroblast growth factor (bFGF) has been implicated as an embryonic mesoderm-inducing factor. It has also been detected in the mesodermally derived fetal and adult reproductive tracts. To address its possible role in the development of the reproductive tract, male and female fetal genital ridges and urogenital (UG) sinuses were transplanted bilaterally under the kidney capsule of syngeneic host rats; the transplants and the hosts were the same sex. Antiserum to bFGF (anti-bFGF) or normal rabbit serum (NRS) was infused into the right renal artery. The transplants on the left uninfused kidney served as internal controls. Upon vascularization, the transplants grow and differentiate essentially normally, but their overall growth after 14 days was reduced by about 40% compared to their growth in situ. Neutralization of endogenous bFGF with anti-bFGF resulted in approximately 41% inhibition of growth in the male genital ridge, but had no effect on the male UG sinus or any component of the female reproductive tract. The growth suppression of the male genital ridge was accompanied by an inhibition of the differentiation of the epididymis. After 7 days of treatment, development of the epididymis was impaired by 75%, and by 14 days, the organ was absent. Previous studies of fetal reproductive tract development have focused on the role of steroids and Mullerian inhibiting hormone. Our studies suggest that bFGF plays a role in the development of the male reproductive tract, especially the epididymis, and further suggest the possible role of this peptide growth factor in a steroid hormone-dependent process.