Is the circadian core temperature rhythm of juvenile rats due to a periodic blockade of thermoregulatory thermogenesis

摘要: Previous studies have demonstrated an endogenous circadian rhythm of core temperature (T c) in suckling-age rat pups. Our aim was to establish whether the low and irregular T c at beginning light phase is caused by a temporary blockade thermoregulatory thermogenesis. We therefore isolated artificially fed 10-day-old pups for 30 h five ambient temperatures (T a), ranging from thermoneutrality severe cold loading, while continuously recording metabolic rate (MR). During maximum MR increased linearily with decreasing T a — as much 260% daily mean (TNMR) so that decreased less than 1°C increasing load. minimum phase, all but lowest fell to, or even below, TNMR amplitude 2 5°C Under most load, however, further decrease prevented increase 135% TNMR. Supplementing synthetic milk noradrenaline (1.2 mg kg−1 h−1) during upto 290% The loose regulation juvenile thus not peripheral impairment thermogenic capacitiy phase.