Kott K S, Moore B J, Fournier L, Horwitz B A
Department of Animal Physiology, University of California, Davis 95616.
Am J Physiol. 1989 Jan;256(1 Pt 2):R174-80. doi: 10.1152/ajpregu.1989.256.1.R174.
Previous studies demonstrated that short photoperiod exposure significantly decreases circulating prolactin levels. The present study investigated the possibility that concomitant changes in brown fat tissue mass, protein content, thermogenic capacity, and carcass composition are dependent on this change in prolactin levels. Male golden (Syrian) hamsters were sham operated and exposed to a short (10L:14D) or long (14L:10D) photoperiod. A third group was implanted with exogenous pituitaries under the right kidney capsule and exposed to a short photoperiod. In experiment I, 4 wk of short- vs. long-photoperiod exposure did not result in significant changes in circulating prolactin levels, nor was there an increase in brown fat mass, protein content, or thermogenic capacity. Four weeks of short-photoperiod exposure did significantly increase carcass lipid content. However, this increase did not occur in hamsters exposed to 4 wk of short photoperiod but made hyperprolactinemic (implanted with two exogenous pituitaries). Ten weeks of short photoperiod significantly reduced circulating prolactin levels. Concomitantly, brown fat mass, protein content, and thermogenic capacity, as well as carcass fat, were increased. These short-photoperiod-induced changes were not observed in similarly exposed hamsters that were made hyperprolactinemic via two implanted pituitaries. In experiment II, similar changes in brown fat and body composition occurred in sham-operated hamsters exposed to 10 wk of short photoperiod. These changes were prevented in hamsters exposed to 10 wk of short photoperiod but made hyperprolactinemic via only one implanted pituitary. These results suggest that decreased prolactin is a necessary condition for the increased brown fat mass, protein content, and thermogenic capacity that occurs when golden hamsters are exposed to short photoperiod.
以往的研究表明，短光照周期暴露会显著降低循环催乳素水平。本研究探讨了棕色脂肪组织质量、蛋白质含量、产热能力和胴体组成的相应变化是否依赖于催乳素水平的这种变化。雄性金黄（叙利亚）仓鼠接受假手术，并暴露于短（10小时光照：14小时黑暗）或长（14小时光照：10小时黑暗）光照周期。第三组在右肾包膜下植入外源性垂体，并暴露于短光照周期。在实验I中，短光照周期与长光照周期暴露4周并未导致循环催乳素水平发生显著变化，棕色脂肪质量、蛋白质含量或产热能力也没有增加。短光照周期暴露4周确实显著增加了胴体脂质含量。然而，这种增加在暴露于短光照周期4周但催乳素水平升高（植入两个外源性垂体）的仓鼠中并未出现。短光照周期10周显著降低了循环催乳素水平。与此同时，棕色脂肪质量、蛋白质含量和产热能力以及胴体脂肪均增加。在通过植入两个垂体使催乳素水平升高的类似暴露仓鼠中未观察到这些短光照周期诱导的变化。在实验II中，暴露于10周短光照周期的假手术仓鼠的棕色脂肪和身体组成发生了类似变化。在暴露于10周短光照周期但仅通过植入一个垂体使催乳素水平升高的仓鼠中，这些变化得到了预防。这些结果表明，催乳素降低是金黄仓鼠暴露于短光照周期时棕色脂肪质量、蛋白质含量和产热能力增加的必要条件。
