ABSTRACT
Toxicology of the excurrent ducts in the male is a relatively new topic, as past efforts have emphasized an understanding of the mechanisms of direct and indirect effects of chemical exposure on the testis. It is difficult to separate direct versus indirect effects on the excurrent ducts because functional impairment of either interstitial cells, Sertoli cells, or germ cells may indirectly affect the function of epithelium downstream. For example, since the epididymis is strongly dependent upon androgen stimulation, any compound that compromises Leydig cell function will decrease androgen concentrations in the blood or rete testis fluid, which in tum will have dramatic effects on epididymal function and thus sperm maturation and fertility. Of course, the overwhelming longterm effect of androgen depletion will be testicular injury, which results in a decline in spermatogenesis and eventually in testicular atrophy. However, short-term effects will be on epididymal function and sperm maturation. Despite the inherent difficulty, it is important that we begin to separate direct from indirect effects of toxicants on the male reproductive tract and to understand how these effects interfere with testicular function as well as impact posttesticular sperm maturation, i.e., fertilizing capability. This chapter will address many of these questions and provide a general overview of structure/function and toxic response of rete testis, efferent ductules, epididymis, seminal vesicles, and prostate. Although the reproductive tract shows considerable similarity between species. it must be emphasized that there can be major differences in structure and function. There are also major regulatory differences between the various regions of the tract. In general, hormonal regulation of the epididymis and male accessory sex organs appears to be under the control of androgens. However, the epithelium
of the rete testis, ductuli efferentes, and initial segment of the epididymis does not appear to be regulated entirely by the androgens, but appears to be under the control of other testicular factors present in the luminal fluid. Thus. it is important in male reproductive toxicology to understand the mechanism of toxicant action on the affected organs, and any species differences in normal structure and function, before attempting to extrapolate data obtained in animal studies to human exposure conditions.
