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Light-dark differences in the effects of ambient temperature on gaseous metabolism in newborn rats
1Department of Physiology, McGill University, Montreal, Quebec, Canada H3G 1Y6.
Insights
Newborn rat pups show higher body temperatures during the dark phase, indicating a higher thermoregulation set point and increased heat production. This suggests internal biological clocks influence body temperature regulation in neonates.
Area of Science:
- Physiology
- Chronobiology
- Neonatal Research
Background:
- Circadian rhythms influence physiological processes, including body temperature, in many species.
- Understanding thermoregulation in newborn mammals is crucial for their survival and development.
- Previous studies suggest diurnal variations in body temperature, but the underlying mechanisms in neonates are not fully elucidated.
Purpose of the Study:
- To investigate whether differences in body temperature between light and dark phases in rat pups are associated with changes in thermoregulatory set points.
- To examine the metabolic responses, specifically oxygen consumption and carbon dioxide production, related to thermogenesis under varying ambient temperatures.
- To explore the role of endogenous circadian changes in regulating body temperature oscillations in newborn rats.
Main Methods:
- Measurements of body temperature (T(b)) in rat pups (7-9 days old) under a 12:12-hour light-dark cycle.
- Assessment of oxygen consumption (VO(2)) and carbon dioxide production (VCO(2)) using an open-flow system.
- Gradual decrease in ambient temperature (T(a)) from 40°C to 15°C to evaluate thermogenic responses.
Main Results:
- Rat pups exhibited consistently higher body temperatures during the dark phase compared to the light phase.
- Oxygen consumption was significantly higher (approximately 30%) in the dark phase across a range of decreasing ambient temperatures, indicating increased thermogenesis.
- The critical ambient temperature triggering increased oxygen consumption was lower in the dark phase, suggesting a higher thermoregulatory set point.
Conclusions:
- The higher body temperature observed in rat pups during the dark phase is linked to an elevated thermoregulatory set point and enhanced metabolic heat production.
- These findings support the hypothesis that endogenous circadian rhythmicity directly influences the set point of thermoregulation in newborn mammals.
- The study highlights the importance of internal biological clocks in mediating daily fluctuations of body temperature during early development.
Abstract:
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).