Effects of photoperiod on androgen-binding protein and sperm fertilizing ability in the hamster

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Abstract
Androgen binding protein (ABP) was detected in both the testis and epididymis of golden hamsters exposed to a long photoperiod (16L:8D). The concentration of ABP in the testis rose from 0.1 pmol/g testis in 2-week-old animals to attain maximum values (3.9 pmol/g testis) at 6-7 weeks, then declined to adult values (1.8 .+-. 0.4 pmol/g testis) after 10-11 weeks of age. In contrast, the ABP concentration of the caput epididymides reached maximum values at 4-7 weeks of age (14 pmol/g tissue) and declined to adult values (4.8 .+-. 1.5 pmol/g tissue) by 10-11 weeks of age. ABP content of the corpus epididymides was maximal (1.0 pmol/g tissue) at 2 weeks of age and thereafter declined to below detectable levels by 10-11 weeks. No ABP could be detected in the cauda epididymides from animals of any age examined. Hamster ABP analysed by steady-state polyacrylamide gel electrophoresis had a relative mobility (Rf) of 0.33 compared to 0.41 for rabbit ABP. Sucrose gradient analysis of hamster ABP indicated a sedimentation coefficient of about 4 S. The binding of [3H]5.alpha.-dihydrotestosterone ([3H]5.alpha.-DHT) to hamster ABP was very rapid with equilibrium occurring within 10 min. The dissociation of [3H]5.alpha.-DHT from hamster ABP was also rapid (t1/2 = 2.77 min). Saturation analysis of ABP from mature animals yielded an apparent dissociation constant of 6.4 nM and an ABP concentration of 1.2 .+-. 0.2 pmol/mg protein. The binding of [3H]5.alpha.-DHT to hamster ABP was inhibited by 5.alpha.-DHT > testosterone > > > oestradiol > cyproterone acetate. Exposure of mature hamsters to a short photoperiod (8L:16D) for 3 weeks resulted in a 42% drop in epididymal ABP levels (10.3 to 4.3 pmol/g tissue). Epididymal ABP further declined so that after 15 weeks in a short photoperiod it was 4% (0.4 pmol/g) of initial values. Accompanying this decrease in epididymal ABP concentrations was a decline in the fertilizing ability of spermatozoa from the distal cauda. When hamsters were transferred from a short to a long photoperiod (16L:8D), epididymal ABP content returned to about 50% of control values within 3 weeks. However, the fertilizing ability of spermatozoa from the cauda epididymides of the animals did not return to control values after a 9-week exposure to a stimulatory photoperiod.