HORMONAL-REGULATION OF SPERMATOGENESIS IN THE HYPOPHYSECTOMIZED RAT -QUANTITATION OF GERM-CELL POPULATION AND EFFECT OF ELIMINATION OF RESIDUAL TESTOSTERONE AFTER LONG-TERM HYPOPHYSECTOMY

Spermatogenesis continues after long-term hypophysectomy (Hx), but mas sive cell degeneration prevents seminiferous tubules from attaining th e full complement of cells. One objective of this study was to determi ne the vulnerable sites for completion of spermatogenesis in long-term Hx rats. It is now known that Leydig cells continue to secrete small amounts of androgen after Hx. A second objective was to determine the cellular sites that are maintained by residual androgen secreted by Le ydig cells post-Hx. Two groups of adult animals were utilized. Both gr oups were Hx for 36 days, but one group of rats received the androgen antagonist flutamide during the 26th through the 36th day of Hx (10 da ys). Germ-cell numbers were quantified using a method that allowed the ir expression as numbers of cells present per hour of development. In the long-term Hx rat, the germ-cell population increased to preleptote ne, but the divisions that led to preleptotene were inefficient due to cell degeneration. Subsequent to preleptotene, there was a gradual lo ss in cells such that there were few germ cells remaining by steps 9-1 3. Flutamide given to Hx rats did not result in a significant differen ce in the numbers of intermediate and type B spermatogonia or signific ant differences in progenitor cells. A significant and major depressio n of cell numbers in Hx-fiutamide-treated rats occurred in the cell di vision of type B spermatogonia to form preleptotene spermatocytes. The re was a less dramatic, although significant, depression of cell numbe rs in Hx-flutamide-treated animals that occurred from preleptotene unt il late pachytene as well as an increased loss of round spermatids at midcycle (Step 5-6). These data demonstrate that cell loss after long- term Hx occurs at numerous phases of spermatogenesis. The data also de monstrate that the presence of residual androgen action after long-ter m Hx results in enhanced germ-cell survival. Although the major blocka ge in cell viability occurs at midcycle steps in the long-term Hx rat, there are several other hormone-sensitive phases of spermatogenesis.