Buchanan B A, Chapin L T, Tucker H A
Department of Animal Science, Michigan State University, East Lansing 48824-1225.
J Pineal Res. 1992 May;12(4):181-9. doi: 10.1111/j.1600-079x.1992.tb00046.x.
Our objective was to suppress the daily surge of melatonin in serum of prepubertal dairy heifers by manipulating intensity of light (Experiment 1) and duration of exposure to light (Experiment 2). Heifers in Experiment 1 were exposed to either 12 hr of darkness (000 lux, control), or 400, 800, or 1,200 lux of light during the last 6 hr of their usual 12-hr nocturnal period. During this 6-hr exposure to various intensities of light, melatonin concentrations were similar to their respective daytime baseline values measured under 400 lux of light, but were 62% to 82% lower than melatonin concentrations during their nocturnal surge period. Suppression of melatonin concentrations was similar between 400 and 1,200 lux of light. In Experiment 2, heifers were exposed to LD 8:16, LD 16:8, LD 20:4, or LD 24:0 photoperiods (1,200 lux) for 4 months. Throughout treatment, concentrations and durations of the melatonin surge were suppressed in the LD 24:0 group and were greatest (during the nocturnal period) in the LD 8:16 group. Concentrations of prolactin in serum were elevated in animals under long days relative to LD 8:16 treatment and respective pretreatment periods. In conclusion, continuous light at an intensity of 1,200 lux suppressed the nocturnal surge of melatonin, but increased secretion of prolactin for at least 4 months in prepubertal heifers.
我们的目标是通过控制光照强度（实验1）和光照时长（实验2）来抑制青春期前奶牛小母牛血清中褪黑素的每日激增。实验1中的小母牛在其通常12小时夜间时段的最后6小时，要么处于12小时黑暗（0勒克斯，对照组），要么处于400、800或1200勒克斯的光照下。在这6小时暴露于不同强度光照期间，褪黑素浓度与在400勒克斯光照下测得的各自白天基线值相似，但比其夜间激增期的褪黑素浓度低62%至82%。400勒克斯和1200勒克斯光照下对褪黑素浓度的抑制相似。在实验2中，小母牛接受8:16、16:8、20:4或24:0光周期（1200勒克斯）处理4个月。在整个处理过程中，24:0光周期组的褪黑素激增浓度和时长受到抑制，而8:16光周期组（在夜间时段）的褪黑素激增浓度和时长最大。与8:16光周期处理及各自的预处理期相比，长日照条件下动物血清中催乳素浓度升高。总之，1200勒克斯强度的持续光照抑制了青春期前小母牛夜间褪黑素的激增，但至少4个月内增加了催乳素的分泌。
