The influence of acute hypoxia and carotid body denervation on thermoregulation during non-rapid eye movement sleep in the developing lamb

We investigated the influence of ambient temperature on the thermoregulator y response to hypoxia in developing lambs before (at 4 and 14 days of age) and after (17 and 30 days of age) carotid body denervation (CBD). Lambs wer e studied during non-rapid eye movement sleep at thermoneutral (23-15 degre es C) and cool (10-5 degrees C) ambient temperatures, during normoxia and a cute hypoxia (inspired oxygen content of 13 %). Measurements of oxygen cons umption, arterial partial pressures of O-2 and CO2, colonic temperature, in cidence of shivering and plasma concentrations of thyroid hormones, cortiso l, insulin and glucose were made under each condition. Oxygen consumption w as higher at cool compared with thermoneutral ambient temperatures and decr eased during hypoxia during cooling at all stages. At 4 days of age, only o ne lamb shivered during cooling in normoxia, but 4 out of 12 lambs shivered during hypoxia and colonic temperature fell, significantly by 0.2 degrees C. At 14 days, 8 out of 12 lambs shivered during cooling, of which 6 contin ued to shiver during hypoxia but colonic temperature did not change signifi cantly. Plasma triiodothyronine concentrations increased on cooling at 4 an d 14 days, an affect that was inhibited by hypoxia at 4, but not 14 days of age. At 17 days of age, i.e. post-CBD, plasma thyroid hormone concentratio ns and oxygen consumption were lower during cold exposure compared with int act lambs at 14 days of age. In CBD lambs, imposing further hypoxia resulte d in colonic temperature falling 0.6 degrees C during cooling, with only 2 out of 10 lambs shivering. Plasma glucose and insulin, but not cortisol, co ncentrations decreased during hypoxia, irrespective of age or CBD. It is co ncluded that hypoxia has an important influence on metabolism and thermoreg ulation, which is modulated by age and environmental conditions. Compromise d carotid body function, in lambs older than 2 weeks of age, can result in severe hypoxia and thermoregulatory dysfunction even with modest environmen tal cooling.