Olsson K, Josäter-Hermelin M, Hossaini-Hilali J, Hydbring E, Dahlborn K
Department of Animal Physiology, Swedish University of Agricultural Sciences, Uppsala.
Comp Biochem Physiol A Physiol. 1995 Apr;110(4):309-17. doi: 10.1016/0300-9629(94)00186-w.
Water intake was studied in six goats during late pregnancy to investigate if heat stress induces primary polydipsia. The goats were fed twice daily or deprived of food for 24 hr to avoid postprandial drinking and induce hyponatremia. Signs of stress was evaluated by determination of plasma cortisol concentration. Ambient temperature was increased from 20 degrees C to 38.0-39.5 degrees C for 5.15 hr. Water temperature was 35 +/- 1 degree C during heat stress. Fed goats started to drink 13 +/- 3 min after the heaters were turned on and water diuresis developed in five of them. The body weight increased simultaneously with decreased plasma Na concentration and osmolality showing that the goats also stored water. During food deprivation, plasma Na concentration and osmolality fell, and plasma aldosterone concentration increased. Despite hyponatremia, food deprived goats started to drink 44 +/- 15 min after the heaters were turned on and then they drank repeatedly. Three of them underwent water diuresis. Hemodilution was observed both in fed and food-deprived goats during heat stress. These results show that heat stress induced primary polydipsia in pregnant goats. It is suggested that stimulating signals from warmth receptors overrode inhibiting influences from receptors signalling hyponatremia and hypoosmolality at the "thirst center" in the hypothalamus. Heat stress did not increase plasma cortisol concentration, but catching sight of food caused an abrupt, short-lasting elevation.
对六只处于妊娠后期的山羊的水摄入量进行了研究，以调查热应激是否会引发原发性烦渴。山羊每天喂食两次，或禁食24小时，以避免餐后饮水并诱发低钠血症。通过测定血浆皮质醇浓度来评估应激迹象。环境温度从20摄氏度升高到38.0 - 39.5摄氏度，持续5.15小时。热应激期间水温为35±1摄氏度。喂食的山羊在加热器打开后13±3分钟开始饮水，其中五只出现水利尿。体重增加的同时血浆钠浓度和渗透压降低，表明山羊也储存了水分。禁食期间，血浆钠浓度和渗透压下降，血浆醛固酮浓度升高。尽管存在低钠血症，禁食的山羊在加热器打开后44±15分钟开始饮水，然后反复饮水。其中三只出现水利尿。在热应激期间，喂食和禁食的山羊均观察到血液稀释。这些结果表明，热应激在怀孕山羊中诱发了原发性烦渴。有人认为，来自温觉感受器的刺激信号克服了来自下丘脑“口渴中枢”中传递低钠血症和低渗透压信号的感受器的抑制作用。热应激并未增加血浆皮质醇浓度，但看到食物会导致其突然短暂升高。
