Stanisiewski E P, Chapin L T, Petitclerc D, Tucker H A
Dept. of Anim. Sci., Michigan State University, East Lansing 48824.
J Anim Sci. 1987 Nov;65(5):1306-11. doi: 10.2527/jas1987.6551306x.
After 8 wk exposure to 8 h of light per day, prolactin (PRL) averaged 18.3 ng/ml of serum in eight male calves. Four calves then received 16 h of light per day; 6 wk later (age 14 wk) PRL averaged 93.8 ng/ml of serum, whereas PRL averaged 36.9 ng/ml of serum in four calves maintained under 8 h of daily light. By wk 20, PRL was not different in calves exposed to 16 or 8 h of daily light, averaging 34.7 and 17.2 ng/ml serum. Testosterone averaged .43 ng/ml of serum at wk 8 but was greater at wk 14 in calves receiving 16 h of light daily when compared with controls receiving 8 h of light (1.92 vs. .97 ng/ml of serum). Testosterone concentrations were not different between photoperiod treatments at wk 20. Luteinizing hormone (LH) concentrations were unaffected by photoperiod. In a second experiment, four male calves were castrated at approximately 2 wk of age while four similar controls were left gonadally intact. After 8 wk exposure to 8 h of light per day, PRL averaged 12.3 ng/ml of serum in all calves. After 6 wk exposure to 16 h of light per day, PRL in serum increased in castrates to 48.0 ng/ml and in controls to 59.8 ng/ml. We conclude that serum concentrations of PRL and testosterone, but not LH, increased in bull calves receiving 16 h of light daily relative to calves receiving 8 h of light, and that the PRL response to photoperiod is independent of the testes. However, 16 h light-induced stimulation of serum concentrations of prolactin is not maintained indefinitely.
在每天光照8小时的条件下暴露8周后，8头雄性犊牛血清中的催乳素（PRL）平均为18.3纳克/毫升。随后，4头犊牛每天接受16小时光照；6周后（14周龄），这些犊牛血清中的PRL平均为93.8纳克/毫升，而另外4头每天维持8小时光照的犊牛血清中的PRL平均为36.9纳克/毫升。到第20周时，每天接受16小时或8小时光照的犊牛血清中的PRL没有差异，分别平均为34.7和17.2纳克/毫升。睾酮在第8周时血清平均为0.43纳克/毫升，但在第14周时，每天接受16小时光照的犊牛的睾酮水平高于每天接受8小时光照的对照组（分别为1.92和0.97纳克/毫升血清）。在第20周时，不同光照周期处理的睾酮浓度没有差异。促黄体生成素（LH）浓度不受光照周期影响。在第二个实验中，4头雄性犊牛在约2周龄时被阉割，同时4头相似的对照组保留性腺完整。在每天光照8小时的条件下暴露8周后，所有犊牛血清中的PRL平均为12.3纳克/毫升。在每天光照16小时的条件下暴露6周后，阉割犊牛血清中的PRL增加到48.0纳克/毫升，对照组增加到59.8纳克/毫升。我们得出结论，相对于每天接受8小时光照的犊牛，每天接受16小时光照的公牛犊血清中PRL和睾酮的浓度增加，但LH浓度未增加，并且PRL对光照周期的反应与睾丸无关。然而，16小时光照诱导的血清催乳素浓度升高不会无限期持续。
