Binding of Steroids by Intact Bovine Sperm1

A new filter assay technique was developed to evaluate spermatozoal binding at 5°C for steroid present at 0.1–5,000 nM. A charcoal-stripping technique was used to reduce the amount of endogenous steroid bound by sperm. Both stripped and non-stripped sperm bound steroids to essentially unsaturable sites. Progesterone was bound with greatest affinity followed by estradiol > dihydrotestosterone > testosterone > androsterone, androstenedione > androstanediol, etiocholanolone. We conclude that very few if any specific, saturable, high affinity steroid-binding sites exist on intact testicular or ejaculated sperm.