Basic FGF-like proteins of 16 and 43 kDa were present in RTF and in the luminal fluid from various epididymal regions of the rat (Figs. 9 and 10). These results suggest that the 43-kDa and 16-kDa bFGF-like proteins in the initial segment could originate from the testis. Previous studies have shown that testicular factors (luminal fluid and spermatozoa) are depleted in the initial segment following 3-day EDL. In this study, the 43-kDa bFGF-like protein was not detected in the homogenate from the initial segment after 3-day EDL (Fig. 10, С and D). birth control pills
The level of this bFGF-like protein in the lumen from various epididymal regions also remained unchanged in comparison to the level in the rete testis when equal amounts of total luminal proteins were loaded in each lane (Fig. 10A). Since protein concentrations of luminal fluid from the rat rete testis, initial segment, caput, and cauda regions are about 1, 20, 2025, and 20-25 jxg/(xl, respectively; unpublished results), the real bFGF-like protein concentration in the lumen of the initial segment would be about 20 times higher than the concentration in rRTF. In this study, the bFGF level in 5 |xg of rRTF protein was found to be approximately equal to that in 5 |xg protein of initial segment fluid (Fig. 10A). This result confirms the previous observation that 90% of water has been reabsorbed from the rete testis to the proximal caput region, and further supports the conclusion that the 43-kDa bFGF-like protein in the luminal fluid of the rat initial segment originates from the testis.