Irvine C H, Alexander S L
Animal & Veterinary Sciences Group, Lincoln University, New Zealand.
Domest Anim Endocrinol. 1994 Apr;11(2):227-38. doi: 10.1016/0739-7240(94)90030-2.
In horses, a circadian rhythm in plasma cortisol concentrations has been reported in some but not all studies. When a rhythm occurred, horses were accustomed to a management routine, comprising stabling, feeding and sometimes exercise, which may entrain a circadian pattern. In this work, we monitored plasma cortisol by collecting jugular blood through indwelling cannulae from four groups: 1): 10 untrained, unperturbed mares grazing excess pasture, bled hourly for 26 hr; 2) 4 mares housed in a barn for 48 hr before sampling every 15 min for 20-24 hr; 3) 5 mares placed in an outdoor yard for sampling every 30 min from 0930-2100 hr; and 4) 4 stabled racehorses in training, bled every 30 min from 0730-2000 hr and once the following morning at 0830 hr. Plasma cortisol showed a similar-timed circadian rhythm (P < 0.0001) in all Group 1 horses, with a peak at 0600-0900 hr, and a nadir at 1800-2100 hr. By contrast, cortisol concentrations did not vary with time in either Group 2 or 3. Neither daily mean nor peak cortisol values differed in Group 1 and 2 (i.e. bled for > or = 20 hr); however nadir values were higher (P < 0.05) in Group 2. In Group 4, cortisol declined (P = 0.004) during the sampling period but had returned to initial concentrations the next morning. Values did not differ from those for Group 1, except between 1000 and 1300 hr when cortisol in Group 4 was lower (P < 0.05). We conclude that a circadian cortisol rhythm exists in horses in the absence of any known cues imposed by humans. However, this rhythm can be obliterated by the minor perturbation of removing the horse from its accustomed environment. By contrast, the rhythm occurs in trained racehorses, suggesting either that they have adapted to their environment thereby allowing an endogenous rhythm to emerge, or that the rhythm is entrained by their daily routine. These observations highlight the difficulties in determining the cortisol status of a horse, since measurements will be affected by time of day, the occurrence of short-term fluctuations, and how accustomed the horse is to its environment.
在马匹中，部分而非所有研究都报道了血浆皮质醇浓度存在昼夜节律。当出现节律时，马匹习惯了一种管理日常，包括圈养、喂食，有时还有运动，这可能会引发一种昼夜模式。在这项研究中，我们通过留置套管从颈静脉采集血液来监测四组马匹的血浆皮质醇：1）10匹未经训练、未受干扰的母马，在过量牧场上放牧，每小时采血一次，共采血26小时；2）4匹母马在采样前在 barn 中饲养48小时，然后每15分钟采样一次，共采样20 - 24小时；3）5匹母马放置在室外院子里，从0930至2100小时每30分钟采样一次；4）4匹圈养的训练中的赛马，从0730至2000小时每30分钟采血一次，并在次日上午0830小时采血一次。所有第1组马匹的血浆皮质醇呈现出类似时间的昼夜节律（P < 0.0001），在0600 - 0900小时达到峰值，在1800 - 2100小时达到最低点。相比之下，第2组和第3组的皮质醇浓度均未随时间变化。第1组和第2组（即采血时间≥20小时）的每日平均皮质醇值和峰值皮质醇值均无差异；然而，第2组的最低点值更高（P < 0.05）。在第4组中，皮质醇在采样期间下降（P = 0.004），但在次日早晨恢复到初始浓度。除了在1000至1300小时期间第4组的皮质醇较低（P < 0.05）外，其值与第1组的值没有差异。我们得出结论，在没有任何已知的人为施加的线索的情况下，马匹中存在昼夜皮质醇节律。然而，将马匹从其习惯的环境中移出这种轻微干扰可能会消除这种节律。相比之下，这种节律在训练有素的赛马中出现，这表明要么它们已经适应了环境，从而使内源性节律得以显现，要么这种节律是由它们的日常活动所引发的。这些观察结果凸显了确定马匹皮质醇状态的困难，因为测量结果会受到一天中的时间、短期波动的发生以及马匹对其环境的适应程度的影响。
