Circadian rhythms of body temperature and activity levels during 63 h of hypoxia in the rat

Abstract

The hypothermic response of rats to only brief ( approximately 2 h) hypoxia has been described previously. The present study analyzes the hypothermic response in rats, as well as level of activity (L(a)), to prolonged (63 h) hypoxia at rat thermoneutral temperature (29 degrees C). Mini Mitter transmitters were implanted in the abdomens of 10 adult Sprague-Dawley rats to continuously record body temperature (T(b)) and L(a). After habituation for 7 days to 29 degrees C and 12:12-h dark-light cycles, 48 h of baseline data were acquired from six control and four experimental rats. The mean T(b) for the group oscillated from a nocturnal peak of 38.4 +/- 0.18 degrees C (SD) to a diurnal nadir of 36.7 +/- 0.15 degrees C. Then the experimental group was switched to 10% O(2) in N(2). The immediate T(b) response, phase I, was a disappearance of circadian rhythm and a fall in T(b) to 36.3 +/- 0.52 degrees C. In phase II, T(b) increased to a peak of 38.7 +/- 0.64 degrees C. In phase III, T(b) gradually decreased. At reoxygenation at the end of the hypoxic period, phase IV, T(b) increased 1.1 +/- 0.25 degrees C. Before hypoxia, L(a) decreased 70% from its nocturnal peak to its diurnal nadir and was entrained with T(b). With hypoxia L(a) decreased in phase I to essential quiescence by phase II. L(a) had returned, but only to a low level in phase III, and was devoid of any circadian rhythm. L(a) resumed its circadian rhythm on reoxygenation. We conclude that 63 h of sustained hypoxia 1) completely disrupts the circadian rhythms of both T(b) and L(a) throughout the hypoxic exposure, 2) the hypoxia-induced changes in T(b) and L(a) are independent of each other and of the circadian clock, and 3) the T(b) response to hypoxia at thermoneutrality has several phases and includes both hypothermic and hyperthermic components.

The influence of a mild thermal challenge and severe hypoxia on exercise performance and serum BDNF

“…This observation might be explained by what is known in the literature as a hypoxia-induced anapyrexia or hypometabolism, in other words the regulated decrease of the body temperature in response to acute hypoxia exposure (Steiner and Branco 2002;Grishin 2011;Cadena and Tattersall 2014). The anapyretic response in combination with metabolic suppression serves as an important protective function to tissues (for example the heart and the brain) that risk damage due to oxygen deficit (Wood 1995) and has been observed in studies with rats (Mortola and Seifert 2000;Bishop et al 2000;Cadena and Tattersall 2014). Recently the first evidence of the existence of this response in humans has been observed (DiPasquale et al 2015).…”

Breathing around the clock: an overview of the circadian pattern of respiration

“…Because the circadian pattern of T b reflects the balance between heat loss and heat production (Refinetti and Menaker 1992), one would expect that hypoxia, by interfering with the thermoregulatory mechanisms, also modifies the normal circadian patterns of T b . Indeed, rats in 10% O 2 for several days, while showing rather small changes in their activity pattern, presented a profound depression in the circadian amplitude of T b and V _ O 2 Fenelon et al 2000;Bishop et al 2000Bishop et al , 2001Seifert and Mortola 2002c). In human subjects, the amplitude of the circadian oscillation of temperatures monitored at some skin locations varied between high altitude and sea level, and the tympanic temperature had a significantly lower oscillation at high altitude (Vargas et al 2001).…”

Chronobiological Aspects of the Heart Rhythm Disorders at the Change of Pulmonary Ventilation in Rat Model

“…The significant hypoventilatory LD differences in the thresholds show the different LD effects of hypoventilation-induced systemic asphyxia on the electrical stability of the rat heart. The higher values in the dark part of the day are probably the result of varying myocardial sensitivity to systemic asphyxia in the LD dependence, although there are more reports referring to the depressive effect of hypoxia on the circadian rhythms in rats (Bishop et al, 2000;Fenelon et al, 2000;, in golden hamsters (Jarsky & Stephenson, 2000), and in humans (Bosco et al, 2003). An important and still unanswered question remains: whether the mechanisms responsible for altered myocardial vulnerability are mobilized mainly by hypoventilation-induced systemic asphyxia and reoxygenation with the additive effect of the LD cycle, or are they mobilized by the factors oscillating in the circadian dependence, with the additive effect of hypoventilation/reoxygenation?…”