Investigations on the Relationship between Sperm Fertilizing Ability and Androgen-Binding Protein in the Hypophysectomized, pregnenoloneenolone-Injected Rat*

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Abstract
Hypophysectomized rats maintained with 2 mg pregnenolone have low plasma testosterone levels, but rete testis levels are normal. This model system was used to examine the importance of androgen-binding protein (ABP) in maintaining high luminal androgen concentrations for the development and maintenance of sperm fertilizing ability in the epididymis. Hypophysectomized rats were injected with pregnenolone (1, 0.5, 0.2 or 0.02 mg/100 g body wt) for 14 days, starting 1 day after surgery. Sham-operated rats and a group of hypophysectomized rats were injected with oils as controls. At the end of the experimental period, sperm fertilizing ability, tissue weights, ABP, and testosterone levels were determined. The 1 and 0.5 mg doses of pregnenolone resulted in rete testis testosterone levels that were 67% and 29%, respectively, of the levels found in sham-operated animals. Plasma testosterone levels were not different from levels found in hypophysectomized, oil-injected controls with any of the pregnenolone doses. The 3 highest doses of pregnenolone resulted in levels of testicular ABP that were not statistically different from sham-operated levels (2 pmol/organ). Epididymal ABP content was maintained at sham-operated control levels (30 pmol/organ) with the 1 mg dose; with the 0.5- and 0.2-mg doses, ABP levels were 76% and 73% of sham-operated levels, respectively. Epididylmal ABP specific content (pmol/100 mg tissue) was maintained at sham-operated control levels with the 1, 0.5, and 0.2 mg dose. Sperm fertilizing ability was maintained at sham-operated control levels with the 3 highest doses of pregnenolone. The 0.02 mg dose of pregnenolone resulted in values that were not statistically different from hypophysectomized, oil-injected control values for all parameters tested. A significant positive correlation existed between ABP and sperm fertilizing ability. Testicular and epididymal ABP levels can be maintained in hypophysectomized rats with pregnenolone treatment alone, and sperm fertilizing ability can be maintained when intraluminal androgen levels are low and ABP levels are near normal. ABP may be important in the maintenance of normal sperm fertilizing ability.