Investigations on the Relationship between Sperm Fertilizing Ability and Androgen-Binding Protein in the Restricted Rat*

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Abstract
The hypothesized relationship between androgen-binding protein (ABP) and sperm maturation was investigated using a mutant rodent: the restricted rat. The seminiferous epithelium of these animals undergoes a spontaneous degeneration, but changes are progressive. Restricted rats in the transition to infertility were used to determine if changes in ABP were related to the decreased fertility found in these animals. Fertilizing ability was determined by insemination of cauda epididymal spermatozoa into hormonally primed female rats and examination of ova for evidence of fertilization 48 h later. Epididymal and testicular tissues were analyzed for ABP using a charcoal assay. Androgen levels were determined by radioimmunoassay. Testicular weights were significantly reduced compared to those of normal littermates in restricted rats at all ages; epididymal weights were significantly reduced in rats 140 days and older. Among restricted rats, sperm fertilizing ability was variable, but was significantly lower than that in normal littermates; it was consistently highest at 90 days of age. Epididymal ABP content (pmol/organ) was significantly reduced in restricted rats at all ages; peak values occurred at 90 days. Testicular ABP content was significantly reduced only in the youngest and oldest animals. Plasma testosterone levels were not statistically lower than those found in normal littermates, and ventral prostate weights were maintained at normal levels in all 4 groups of animals. A significant positive correlation existed between sperm fertilizing ability and epididymal ABP, but not between sperm fertilizing ability and plasma testosterone. Since ABP is an index of Sertoli cell function, sperm fertilizing ability evidently is closely related to Sertoli cell function and/or ABP.