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Maintenance of convective requirement during recovery from moderate heat stress in newborn mice
Author(s) -
Avraam Joanne,
Frappell Peter B
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.6.a1444-a
Subject(s) - hyperthermia , hypothermia , overheating (electricity) , thermoregulation , anesthesia , metabolic rate , thermogenesis , ventilation (architecture) , hypoxia (environmental) , chemistry , oxygen , medicine , physics , mechanical engineering , organic chemistry , quantum mechanics , engineering , obesity
Hypothermia often provides a regulated protective mechanism that improves survival. In contrast, overheating may result in disruption of cerebral function, impacting upon respiratory/thermal control centers. Hyperthermia in newborns, particularly if accompanied by hypoxia, is associated with diminished arousals, increased apneas and failure of autoresuscitation. Recovery from hyperthermia is associated with an induced hypothermia which is believed to be a thermoregulatory phenomenon. Whether a hyperthermia induced hypothermia following heat stress occurs in newborn mice with limited thermoregulatory ability is unknown, and whether this affects the tight linkage between ventilation and metabolic rate normally maintained in hypothermic newborns remains to be elucidated. Newborn (day 2 and 7) pepN mice fitted with a small face mask and placed in an open flow respirometer were exposed to normoxia and initial ambient temperatures (Ta) of either 30°C, 32°C or 34°C for 40 min, after which Ta was decreased to and subsequently increased from 18°C at a rate of 0.5°C/min. Metabolic rate (rates of oxygen consumption and CO 2 production), ventilation (VE) and body temperature (Tb) were measured continuously. For both ages, nest Tb was ~30°C and the Tb‐Ta difference at day 2 and 7 was ~1°C or 2°C, respectively. In response to cooling from Ta = 30°C or 32°C both ages were capable of limited thermogenesis; in response to cooling from Ta = 34°C thermogenic effort was ablated. Irrespective of the initial Ta, the convective requirement (i.e. VE/metabolic rate) was maintained during heating and cooling for a given Ta; though the convective requirement tended to be higher in mice initially exposed to 34°C. The results support the notion that following moderate overheating and during recovery hypothermia the mechanisms that couple ventilation to metabolic rate are not impaired.