Rats prefer ambient temperatures out of phase with their body temperature circadian rhythm

Rats placed in thermally graded enclosures cyclically selected ambient temperatures about 195 degrees out of phase with the circadian variations of their hypothalamic temperature. This finding cannot be explained by the generally accepted assumption that body temperature circadian rhythm is due to a cyclic shift of the set-point temperature.     

普鲁卡因—芬太尼静脉麻醉下体温及温度调节反应的研究

全麻下机体的体温调节反应通常被抑制,但由于全麻中肌肉松驰药的应用,机体唯一的体温调节反应只可能是外周血管收缩和非寒颤性产热。为估计麻醉对体温调节反应的影响,作者应用皮肤温差级数(前臂——指尖温差)及食道温度监测方法对40例ASA分级Ⅰ——Ⅱ级行胃癌根治术的病人进行了观察。结果示全麻病人术中存在着活跃的温度调节反应,其主要方式为外周血管收缩和非寒颤性产热。     

桂枝汤对体温双向调节作用的机理探讨──对蛙皮素作用的影响

桂枝汤能抑制蛙皮素对冷环境中大鼠的降温效应，并不影响等效价蛙皮素及其受体拮抗剂Ｄ－苯丙＾１２－蛙皮素合并脑室注射引起的体温改变，亦能翻转Ｄ－苯丙＾１２－蛙皮素在发热大鼠上的升温作用，提示桂枝汤对体温的双向调节，部分通过对下丘脑体温调节中枢中蛙皮素受体的调节起作用。     

Metabolic heat production and cold tolerance during cold stress of different intensity of adult and aged male C57BL/6J mice

Adult and aged male C57BL/6J mice were subjected to a 3-h cold stress test at either 24°C, 18°C, 12°C, or 6°C. Body mass was measured before the test, and colonic temperature, O₂ consumption, and CO₂ production were measured during the test. The slopes of colonic temperature over time of test and the mean metabolic heat production were calculated for each animal. While adult mice had a relatively small reduction in colonic temperature during the test at all four ambient temperatures, in the aged mice ambient temperatures resulted in steeper reductions of colonic temperature. In adult mice, an increase in metabolic heat production was proportional to ambient cold. The thermogenic response of aged mice at 24°C and at 18°C was similar to adult mice, suggesting that the ability of aged mice to respond to cold by increasing heat production does not diminish with age. However, in aged mice metabolic heat production at 12°C and 6°C was significantly below that of adult mice, which indicated a reduced capacity for thermogenesis.     

Involvement of adrenergic receptor mechanisms within hypothalamus in the fever induced by amphetamine and thyrotropin-releasing hormone in the rat

Summary The mechanisms underlying the thermal effects induced by intrahypothalamic administration of either d-amphetamine or thyrotropin-releasing hormone (TRH) has been investigated in conscious rats. Direct administration of d-amphetamine (1–10g in 1l) or TRH (1–4g in 1l) into the preoptic anterior hypothalamus caused hyperthermia or fever at the ambient temperature (T_a 8, 22 and 30 °C) studied. The fever induced by d-amphetamine or TRH was due to increased metabolic heat production at T_a 8 °C, while at T_a 30 °C the fever was due to cutaneous vasoconstriction in the rat. At T_a 22 °C, the fever was due to both increased metabolism and cutaneous vasoconstriction. Furthermore, the fever induced by intrahypothalamic administration of TRH was greatly reduced by pretreatment with intrahypothalamic administration of either yohimbine (a blocking agent of alpha-adrenergic receptors), phentolamine (a blocking agent of alpha-adrenergic receptors) or DL-propranolol (a blocking agent of beta-adrenergic receptors) in the rat. However, the fever induced by d-amphetamine was antagonized by pretreatment with yohimbine or phentolamine, but not with DL-propranolol in the rat. These observations indicate that the adrenergic receptor mechanisms within the hypothalamus are involved in the fever induced by both d-amphetamine and TRH.     

Effect of delivery mode on postpartum neonatal body temperatures

Objective: It is known that general and local anesthesia practices disrupt the delicate balance of thermoregulation center which is already sensitive to very tiny differences of temperatures in a normal subject. We aimed to evaluate and compare the rectal temperatures of newborns born with normal vaginal delivery and cesarean section.

Methods: We performed a prospective study of 106 term newborn – 40 born with normal vaginal delivery (group 1) and 66 born with cesarean section [51 spinal anesthesia (group 2), 15 general anesthesia (group 3)]. Only term babies were included in the study. Babies of eclamptic, pre-eclamptic and diabetic mothers and babies with chronic systemic diseases were excluded. Pregnants who underwent elective cesarean section were included in the study. Adolescent pregnants, pregnants with increased risks and pregnants with complicated operations were excluded. Mothers’ temperatures were measured before and after the interventions. Rectal temperatures of the babies were measured immediately after birth.

Results: Environmental temperature was maintained at 22–24?°C. Pre-operative mother temperatures were 36.31?±?0.30?°C in group 1, 36.36?±?0.26?°C in group 2 and 36.39?±?0.19?°C in group 3 (p?=?0.414). Post-operative mother temperatures were 36.39?±?0.27?°C in group 1, 36.29?±?0.31?°C in group 2 and 36.25?±?0.28?°C in group 3 (p?=?0.215). Rectal temperatures of the babies born with normal vaginal delivery were significantly higher than the others. It was lowest in the general anesthesia group (37.5?±?0.6?°C, 37.2?±?0.2?°C and 36.8?±?0.4?°C in group 1, 2 and 3, respectively). The temperature differences between groups were statistically significant p?<?0.001).

Conclusions: In conclusion, it is worthy to note that temperatures of the newborns can differ according to the delivery mode. Physicians and health professionals that take care of the newborns should be aware of this difference.     

Exertional rhabdomyolysis in a collegiate american football player after preventive cold-water immersion: a case report

Objective:

To describe a case of exertional rhabdomyolysis in a collegiate American football player after preventive cold-water immersion.

Background:

A healthy man (19 years old) participated in full-contact football practice followed by conditioning (2.5 hours). After practice, he entered a coach-mandated post-practice cold-water immersion and had no signs of heat illness before developing leg cramps, for which he presented to the athletic training staff. After 10 minutes of repeated stretching, massage, and replacement of electrolyte-filled fluids, he was transported to the emergency room. Laboratory tests indicated a creatine kinase (CK) level of 2545 IU/L (normal range, 45–260 IU/L), CK-myoglobin fraction of 8.5 ng/mL (normal < 6.7 ng/mL), and CK-myoglobin relative index of 30% (normal range, 25%– 30%). Myoglobin was measured at 499 ng/mL (normal = 80 ng/mL). The attending physician treated the athlete with intravenous fluids.

Differential Diagnosis:

Exercise-associated muscle cramps, dehydration, exertional rhabdomyolysis.

Treatment:

The patient was treated with rest and rehydration. One week after the incident, he began biking and swimming. Eighteen days later, the patient continued to demonstrate elevated CK levels (527 IU/L) but described no other symptoms and was allowed to return to football practice as tolerated. Two months after the incident, his CK level remained high (1900 IU/L).

Uniqueness:

The athlete demonstrated no signs of heat illness upon entering the cold-water immersion but experienced severe leg cramping after immersion, resulting in a diagnosis of exertional rhabdomyolysis. Previously described cases have not linked cold-water immersion with the pathogenesis of rhabdomyolysis.

Conclusions:

In this football player, CK levels appeared to be a poor indicator of rhabdomyolysis. Our patient demonstrated no other signs of the illness weeks after the incident, yet his elevated CK levels persisted. Cold-water immersion immediately after exercise should be monitored by the athletic training staff and may not be appropriate to prevent muscle damage, given the lack of supporting evidence.