DISCUSSION(4)

Since oRTF contains growth factors and a number of growth factors are produced by the testis, it seems possible that growth factors could be candidates in RTF for factors that regulate GGT catalytic activity and GGT protein level in the initial segment. Possible candidates include bFGF and EGF, for several reasons: 1) both growth factors are produced by testis [32—40], 2) both bFGF and EGF activity have been observed in homogenates of human and/or bovine epididymis, 3) bFGF gene is expressed in the young rat epididymis, and 4) EGF receptor is present in mouse and monkey epididymis.

Therefore, bFGF and EGF were used to test the hypothesis that growth factors regulate GGT catalytic activity and GGT protein level. Results showed that only bFGF, not EGF, recovered GGT catalytic activity in the rat initial segment following EDL for 3 days (Fig. 5). Even a high concentration of EGF (100 ng/ml) did not recover GGT catalytic activity in the rat initial segment following 3-day EDL (unpublished results). That cycloheximide, a protein synthesis inhibitor, blocked the function of bFGF (Fig. 5) suggests that protein synthesis is required in order for bFGF to recover GGT catalytic activity.