Comparative labelling of rat epididymal spermatozoa by intratesticularly administered 65ZnCl2 and [35S]cysteine

Abstract

Spermatozoa of rats injected intratesticularly with 20 .mu.Ci 65ZnCl2 and 10 .mu.Ci [35S]cysteine were collected from the caput and cauda of the epididymis at 2, 6, 10, 14, 18, 22 and 28 days after injection. The highest specific activities for each isotope were observed in spermatozoa from the caput on day 10. Maximal levels in spermatozoa from the cauda were obtained on days 14 and 18 for 35S and day 18 for 65Zn. Estimation of the relative behavior of 65Zn and 35S by calculation of 65Zn/35S ratios suggested the following items. 35S associated with spermatozoa arrived in the epididymis slightly in advance of 65Zn and was probably incorporated more readily into proteins of very late spermatids. About 60% of 65Zn was lost from spermatozoa and 75% from isolated sperm heads during transit from caput to cauda, assuming total retention of 35S. Retention of 65Zn by the seminiferous epithelium was superior to that of [35S]cysteine, as indicated by increasing 65Zn/35S ratios following the days of peak-specific activity in both caput and cauda epididymidal spermatozoa. Only small percentages of either isotope were recovered in isolated sperm heads indicating that the primary sites of labeling were in the sperm tail. Superior retention of 65Zn by testis was confirmed by increasing 65Zn/35S ratios in individual fractions of testicular homogenates between 2 and 10 days after injection. Both isotopes appeared to be transferred from the testis cytosol to particulate material during this period.