RESUMEN
The aim of this study was to determine whether the circadian cycle of core temperature (Tc) and oxygen consumption (VO2) in juvenile rats is correlated with changes in the thermogenic activity of brown adipose tissue (BAT). Nine-day-old rat pups derived from two colonies with 12:12 h light-dark cycles 180 degrees out of phase were artificially reared in continuous light for 12-48 h while Tc and VO2 were recorded. For measurement of GDP binding half the pups from each colony were killed during the maximum phase of their circadian Tc cycle and the other half during the minimum phase. During the maximum phase (0.5-2 h after lights-off in the colony of origin), when Tc was 36.1 +/- 0.1 degrees C, GDP binding (pmol/mg protein) was 575 +/- 31 (n = 19). During the minimum phase (0.5-2 h after lights-on), when Tc was 32.9 +/- 0.5 degrees C, GDP binding was 361 +/- 47 (n = 19). Moreover, the correlations between Tc, VO2, and GDP binding determined during the maximum plateau of the circadian cycle differ substantially from those determined during the minimum phase. Consequently, developmental studies of thermoregulation and BAT activity in suckling pups are seriously compromised if circadian phase is neglected.
Asunto(s)
Tejido Adiposo Pardo/fisiología , Regulación de la Temperatura Corporal , Ritmo Circadiano , Tejido Adiposo Pardo/efectos de los fármacos , Tejido Adiposo Pardo/metabolismo , Animales , Temperatura Corporal/efectos de los fármacos , Guanosina Difosfato/metabolismo , Consumo de Oxígeno/efectos de los fármacos , Propranolol/farmacología , Ratas , Ratas Zucker , Maduración SexualRESUMEN
To find out whether or not juvenile rats can sustain circadian rhythms of core temperature (Tc) in the absence of diurnal cues, we continuously recorded Tc for 12 days in isolated pups artificially reared in continuous dim light. Possible effects of uncontrolled environmental 24-h cycles were excluded by simultaneously studying pups born on the same day to two mothers entrained to 12:12 h light-dark cycles 180 degrees out of phase. Age-dependent changes were discriminated from the effects of sustained isolation by comparing Tc records between pups isolated from 10 or from 4 days of age (late- or early-isolated pups). Both groups of pups showed Tc cycles in phase with the light cycle in the colony of origin and with highest amplitudes from 10 to 13 days of age. Tc cycles with a period length close to 24 h could be seen through the 12th day of artificial rearing for early-isolated pups but only until the 6th day for late-isolated pups. In the third postnatal week the rhythm faded gradually. Self-sustained circadian Tc rhythms observed in isolated 1- to 2-wk-old pups demonstrate a functional endogenous clock in the juvenile rat.