The Influence of Acute Hypoxia and Carotid Body Denervation on Thermoregulation During Non‐Rapid Eye Movement Sleep in the Developing Lamb

Abstract

summaryWe investigated the influence of ambient temperature on the thermoregulatory 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 were studied during non-rapid eye movement sleep at thermoneutral (23-15°C) and cool (10-5°C) ambient temperatures, during normoxia and acute hypoxia (inspired oxygen content of 13%). Measurements of oxygen consumption, arterial partial pressures of Oµ and COµ, colonic temperature, incidence of shivering and plasma concentrations of thyroid hormones, cortisol, insulin and glucose were made under each condition. Oxygen consumption was higher at cool compared with thermoneutral ambient temperatures and decreased during hypoxia during cooling at all stages. At 4 days of age, only one lamb shivered during cooling in normoxia, but 4 out of 12 lambs shivered during hypoxia and colonic temperature fell, significantly, by 0·2°C. At 14 days, 8 out of 12 lambs shivered during cooling, of which 6 continued to shiver during hypoxia but colonic temperature did not change significantly. Plasma triiodothyronine concentrations increased on cooling at 4 and 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 concentrations and oxygen consumption were lower during cold exposure compared with intact lambs at 14 days of age. In CBD lambs, imposing further hypoxia resulted in colonic temperature falling 0·6°C during cooling, with only 2 out of 10 lambs shivering. Plasma glucose and insulin, but not cortisol, concentrations decreased during hypoxia, irrespective of age or CBD. It is concluded that hypoxia has an important influence on metabolism and thermoregulation, which is modulated by age and environmental conditions. Compromised carotid body function, in lambs older than 2 weeks of age, can result in severe hypoxia and thermoregulatory dysfunction even with modest environmental cooling.

The Role of Brown Adipose Tissue and Energy Metabolism in Mammalian Thermoregulation during the Perinatal Period

“…In contrast, in precocial species such as lambs, maturity of BAT occurs 40 days before birth, peaks at birth, and rapidly decreases in the first 10 post-natal days. In this species, birth is also accompanied by an increase in voluntary muscle activity and the onset of shivering thermogenesis, a response depending on the BAT function and the magnitude of the thermal challenge [ 110 , 130 , 131 ]. Cannon and Needergaard [ 132 ] mentioned that the biochemical thermogenic index of BAT (known as the total amount of UCP1 per body weight) and its physiological capacity (the increase in O 2 after noradrenaline administration) are events that follow the same pattern in precocial and altricial species, suggesting that in altricial neonates BAT recruitment might be an adaptive response to extrauterine life that triggers the development of BAT during the first days after birth.…”