NEUROTROPHIC FACTORS IN THE RAT PENIS

An intact nerve supply is essential for normal erectile function. We h ave undertaken a study to examine the presence and synthesis of growth factors of the penis that support neural function. Extracts were obta ined from deskinned penises of Sprague-Dawley rats, aged 3, 6 and 10 w eeks, representing prepubertal, pubertal and postpubertal states. Peni le extracts were subjected to Northern blot analysis to evaluate expre ssion of nerve growth factor-beta (beta-NGF)-mRNA, PC-12 bioassay to q uantitate the nerve growth promoting activity and immunoassay to detec t the amount of beta-NGF protein. These initial experiments showed a d isproportionately abundant level of nerve growth promoting activity as compared with the levels detected with the immunoassay. The PC-12 bio assay is sensitive to both beta-NGF and fibroblast growth factors (FGF s). To further investigate these findings, the bioassay was conducted again after heparin chromatography, with beta-NGF receptor blockade, o r with the addition of anti-beta-NGF, anti-basic-FGF, or anti-acidic-F GF. These studies confirmed that the abundant nerve growth promoting a ctivity in the rat penis is due largely to basic FGF. In conclusion, t he neurotrophin NGF is expressed in the rat penis at levels consistent with its expression in other peripheral tissues. Basic-FGF, on the ot her hand, has been detected at levels far in excess of NGF. Since erec tile function is dependent on the integrity of the vascular structure and its intact innervation and since basic FGF presents as an abundant penile growth factor with both angiogenic and neurotrophic activities , basic FGF might play a significant role in erectile physiology.