ANDROGEN-BINDING PROTEIN SECRETION AND ENDOCYTOSIS BY PRINCIPAL CELLSIN THE ADULT-RAT EPIDIDYMIS AND DURING POSTNATAL-DEVELOPMENT

Androgen binding protein (ABP) has been shown to be secreted by Sertol i cells and to be actively taken up by the efferent ducts and proximal caput epididymidis and, yet, to be present at high concentrations in epididymal fluids. In the present study, ABP was immunolocalized by li ght microscopy in epithelial cells of the efferent ducts and epididymi s of adult rats and during postnatal development and by electron micro scopy in specific organelles within these cells. In adults, the effere nt ducts actively endocytosed Sertoli cell-derived ABP. In the epididy mis, principal cells displayed a variable staining reminiscent of a ch eckerboardlike pattern, with cells being intensely, moderately, or wea kly reactive throughout their cytoplasm or unreactive. In the electron microscope, reactive cells displayed a labeling of their Golgi appara tus and secretory Vesicles indicative of an epididymal-secreted form o f ABP. However, labeling was also noted over endosomes of principal ce lls, but only of the initial segment and intermediate zone, which, alo ng with labeling of coated pits and vesicles, indicated that ABP was a lso endocytosed by principal cells of these regions. The postnatal stu dy revealed that principal cells attained an adultlike staining patter n indicative of secretion in a region-specific manner at different age s, suggesting that ABP secretion is regulated by different factors. Li gation of the efferent ducts of 15-day-old animals revealed no reactio n along the entire epididymis in animals sacrificed at later ages, sug gesting the importance of luminal testicular factors in its regulation during development. In addition, as in the adult, ABP was also endocy tosed by principal cells, but only in the initial segment and intermed iate zone. Taken together, the present results indicate that secretion of ABP occurs along the entire epididymis, whereas endocytosis is reg ion specific. The functional role of ABP in the epididymis in relation to sperm maturation is discussed.