Light-dark differences in the effects of ambient temperature on gaseous metabolism in newborn rats.
Body temperature (T(b)) of rat pups (7-9 days old) raised under a 12:12-h light-dark (L-D) regimen (L: 0700-1900, D: 1900-0700) was consistently higher in D than in L by approximately 1.1 degrees C. We tested the hypothesis that the L-D differences in T(b) were accompanied by differences in the set point of thermoregulation. Measurements were performed on rat pups at 7-9 days after birth. O(2) consumption (VO(2)) and CO(2) production (VCO(2)) were measured with an open-flow method during air breathing, as ambient temperature (T(a)) was decreased from 40 to 15 degrees C at the constant rate of 0.5 degrees C/min. At T(a) >/=33 degrees C, VO(2) was not significantly different between L and D, whereas VCO(2) was higher in L, suggesting a greater ventilation. Over the 33 to 15 degrees C range the VO(2) values in D exceeded those in L by approximately 30%. Specifically, the difference was contributed by differences in thermogenesis at T(a) = 30 to 20 degrees C. As T(a) was decreased, the critical temperature at which VO(2) began to rise was lower in L. We conclude that the higher T(b) of rat pups in D is accompanied by a higher set point for thermoregulation and a greater thermogenesis. These results are consistent with the idea that, in newborns, endogenous changes in the set point of thermoregulation contribute to the circadian oscillations of T(b).
Seifert
E L
EL
Department of Physiology, McGill University, Montreal, Quebec, Canada H3G 1Y6.
Mortola
J P
JP
D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism / Q000502:physiology*; D001831:Body Temperature / Q000502:physiology / Q000528:radiation effects; D001833:Body Temperature Regulation / Q000502:physiology / Q000528:radiation effects; D002245:Carbon Dioxide / Q000378:metabolism*; D002940:Circadian Rhythm / Q000502:physiology; D003624:Darkness; D008027:Light; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013696:Temperature
D002245:Carbon Dioxide; D010100:Oxygen