Diekman M A, Braun W, Peter D, Cook D
Department of Animal Sciences, Purdue University, West Lafayette, IN 47907-1151, USA.
J Anim Sci. 2002 Nov;80(11):2949-52. doi: 10.2527/2002.80112949x.
To determine whether secretory patterns of melatonin change throughout the seasons in mares, blood samples were drawn byvenipuncture from nine mares at noon and midnight for five successive days at monthly intervals from August through July at the University of Missouri in Columbia, MO. In addition, during September, December, March, and June, blood samples were drawn from indwelling catheters at 2-h intervals for 48 or 72 h. Mares were predominantly Quarter Horses weighing approximately 450 kg and ranged from 3 to 12 yr of age. Mares were housed in outdoor paddocks with three-sided run-in sheds for shelter. During the noon and midnight bleeding period, mares were placed in a larger open-sided barn with outside runs. Mares remained outdoors with the barn being used as a shelter in the event of inclement weather. All lights in the shed were converted to red light. Often, moonlight provided enough illumination to collect blood samples. Mares were returned to their normal paddock after each sampling period. For analysis of data, a mare was considered to be cycling if serum concentrations of progesterone were greater than 1 ng/ mL. For a mare to be classified as exhibiting a nocturnal rise of melatonin, serum concentrations of melatonin had to be at least two times greater at midnight than at noon. By month, a relationship did not exist (chi2; P > 0.05) among mares that were exhibiting estrous cycles and exhibiting nocturnal rises of melatonin. Likewise, examination of serum profiles of melatonin taken at 2-h intervals for 48 h revealed considerable variation among mares throughout the seasons. A nocturnal rise in serum melatonin was observed only in June (P < 0.02). In March and December, serum melatonin was greater in cycling mares than noncycling mares, but the elevation was not associated with light-dark periods (P < 0.01). Two of the mares exhibited estrous cycles throughout the seasons but melatonin secretion in these two mares were similar to that observed in the seven mares that demonstrated seasonal anestrous. From these results, it does not appear that changes in serum concentrations of melatonin are used as a cue to regulate cyclic activity in the mare throughout the seasons.
为了确定母马体内褪黑素的分泌模式是否随季节变化，在密苏里大学哥伦比亚分校，于8月至次年7月期间，每月间隔连续5天，在中午和午夜对9匹母马进行静脉穿刺采血。此外，在9月、12月、3月和6月期间，通过留置导管每隔2小时采集血样，持续48或72小时。母马主要是体重约450公斤的四分之一马，年龄在3至12岁之间。母马被安置在有三面可进入的棚舍以供遮蔽的户外围场中。在中午和午夜采血期间，母马被安置在一个更大的有开放式边墙的马厩里，外面有跑道。母马一直待在户外，马厩在恶劣天气时用作遮蔽处。棚舍内所有灯光都换成了红灯。通常，月光提供了足够的照明来采集血样。每次采样期结束后，母马被放回它们正常的围场。为了分析数据，如果孕酮的血清浓度大于1纳克/毫升，则认为母马处于发情周期。要将一匹母马归类为表现出褪黑素夜间升高，午夜时褪黑素的血清浓度必须至少比中午时高两倍。按月来看，处于发情周期和表现出褪黑素夜间升高的母马之间不存在关系（卡方检验；P > 0.05）。同样，对每隔2小时采集48小时的褪黑素血清谱进行检查发现，母马在整个季节中存在相当大的差异。仅在6月观察到血清褪黑素夜间升高（P < 0.02）。在3月和12月，处于发情周期的母马血清褪黑素水平高于非发情周期的母马，但这种升高与明暗周期无关（P < 0.01）。其中两匹母马在整个季节都表现出发情周期，但这两匹母马的褪黑素分泌与另外七匹表现出季节性乏情的母马相似。从这些结果来看，似乎血清褪黑素浓度的变化并不是母马在整个季节中调节发情周期活动的线索。
