Ambient temperature modulates hypoxic-induced changes in rat body temperature and activity differentially

Abstract

When rats, acclimated to an ambient temperature (T(a)) of 29 degrees C, are exposed to 10% O(2) for 63 h, the circadian rhythms of body temperature (T(b)) and level of activity (L(a)) are abolished, T(b) falls to a hypothermic nadir followed by a climb to a hyperthermic peak, L(a) remains depressed (Bishop B, Silva G, Krasney J, Salloum A, Roberts A, Nakano H, Shucard D, Rifkin D, and Farkas G. Am J Physiol Regulatory Integrative Comp Physiol 279: R1378-R1389, 2000), and overt brain pathology is detected (Krasney JA, Farkas G, Shucard DW, Salloum AC, Silva G, Roberts A, Rifkin D, Bishop B, and Rubio A. Soc Neurosci Abstr 25: 581, 1999). To determine the role of T(a) in these hypoxic-induced responses, T(b) and L(a) data were detected by telemetry every 15 min for 48 h on air, followed by 63 h on 10% O(2) from rats acclimated to 25 or 21 degrees C. Magnitudes and rates of decline in T(b) after onset of hypoxia were inversely proportional to T(a), whereas magnitudes and rates of T(b) climb after the hypothermic nadir were directly proportional to T(a). No hyperthermia, so prominent at 29 degrees C, occurred at 25 or 21 degrees C. The hypoxic depression of L(a) was least at 21 degrees C and persisted throughout the hypoxia. In contrast, T(a) was a strong determinant of the magnitudes and time courses of the initial fall and subsequent rise in T(b). We propose that the absence of hyperthermia at 21 and 25 degrees C as well as a persisting hypothermia may protect the brain from overt pathology.

Autonomic Nervous System under Ketamine/xylazine and Pentobarbital Anaesthesia in a Wistar Rat Model: A Chronobiological View

“…Similar, but probably more pronounced rhythm alterations occur in rats anaesthetized with pentobarbital. Other explanations for the modulation of daily rhythmicity may be found in the studies by Mortola and Seifert (2000), Bishop et al (2001), Bosco et al (2003), Kaplan et al (2003) and Mortola (2007). The fact that hypoxia modifies the circadian oscillation of important variables, such as body temperature and metabolism, may lead to the expectation that the daily rhythms of many functions are disrupted by hypoxia according to their relationships and connection with the primary variables.…”

Ventilatory and metabolic responses to hypoxia in the smallest simian primate, the pygmy marmoset

“…This practice may soon change, because clinical studies examining the feasibility and ethics of allowing a natural "hypothermia"' in infants during asphyctic episodes are beginning (42). The issue of therapeutic hypothermia is complicated, and recent work on long-term hypoxic exposure shows that T b returns to normal (4,35) after 24 h of hypoxic exposure, emphasizing that the benefits offered through lower T b may only be transient. This long-term response is not well understood and warrants further investigation.…”

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).…”