Early studies have shown that spotted locoweed (Astragalus lentiginosus) has an adverse effect on male reproduction. Rams fed locoweed showed a reduced number of primary and secondary spermatocytes and spermatids in the testis, and of spermatozoa in the epididymis and vas deferens. In addition, the Sertoli cells and other epithelial cells were severely vacuolated. Swainsonine, an indolizidine alkaloid, has been identified as the sole or principal toxin in locoweed and perhaps in the plants of genus Swainsona. The toxin is an inhibitor of lysosomal alpha-D-mannosidase, cytosolic alpha-D-mannosidase, and Golgi mannosidase II. The in vitro and in vivo inhibition of Golgi mannosidase II induces the production of abnormal glycoproteins. Since epididymis-mediated modifications of sperm-surface glycoproteins are believed to be important for sperm-egg interactions, we initiated studies to determine effects of swainsonine on processing and catabolism of N-linked glycoproteins in male reproductive tissues. The results presented in this report indicate that feeding of the alkaloid led to accumulation of mannose-rich oligosaccharides (OS) in the testis and epididymis of rats. The major OS was purified from the reproductive tissues of swainsonine-fed rats, and its structure was deduced by comparison of the size of the OS before and after treatment with jack bean alpha-D-mannosidase, and by affinity column chromatography. In addition, the rat epididymal epithelial cells produced abnormal glycoproteins when cultured in the presence of the toxin. This result provides indirect evidence for the presence of a swainsonine-sensitive mannosidase II-like processing enzyme in the epididymal epithelial cells.(ABSTRACT TRUNCATED AT 250 WORDS)