Effect of castration on epididymal sperm storage in male musk shrews (Suncus murinus) and mice (Mus musculus)

Reproductively mature male musk shrews and mice were bilaterally castrated. Epididymal sperm numbers and motility were assessed 0, 2, 4 and 6 weeks after surgery. Seminal vesicle weights and plasma concentrations of total androgens were also measured. In male musk shrews, 30% of the original epididymal sperm numbers were still present 2 weeks after castration and motile spermatozoa were present in 2 of 7 individuals. By 4 and 6 weeks after castration the numbers of spermatozoa remaining declined to about 10% and no sperm motility was noted. Seminal vesicle weights were maintained at about 30% of their original size even up to 6 weeks after castration. In male mice, epididymal sperm numbers, seminal vesicle weights, and androgen levels declined more dramatically after castration. Although androgen concentrations in gonadally intact male musk shrews were approximately 50% of the values in male mice, after castration the concentrations in musk shrews were approximately 2-fold higher than in mice at all times. The results suggest that post-castration retention of epididymal sperm and seminal vesicle weights in the male musk shrew as compared with male mice, is facilitated either by a relatively greater adrenal contribution to circulating androgen levels and/or greater target tissue sensitivity.