Effect of ambient temperature during 1st day of life on thermoregulation in lambs delivered by cesarean section.
We examined the effect of delivering near-term twin lambs by cesarean section into a warm (30 degrees C) or cool (15 degrees C) ambient temperature on the control of thermoregulation. Heat production was measured 20-30 h after birth during non-rapid-eye-movement sleep at 29 and 14 degrees C. At 29 degrees C there was no difference in heat production between groups, but at 14 degrees C cool-delivered (CD) lambs exhibited a 62% greater metabolic response. Irrespective of delivery temperature, 15 of the 18 lambs used shivering thermogenesis during cold exposure, indicating a reduction in the ability to use nonshivering thermogenesis in brown adipose tissue (BAT). Mean plasma concentrations of thyroxine and triiodothyronine were 35 and 45% greater, respectively, in CD lambs than in warm-delivered lambs. The level of guanosine 5'-diphosphate binding in BAT was lower than in normally delivered lambs and was not different between CD and warm-delivered lambs. Cesarean section delivery prevents the rise in BAT thermogenic activity, which results in an increased reliance on shivering thermogenesis to maintain colonic temperature. Under these conditions, delivery into a cool environment increases the plasma concentration of thyroid hormones, which benefits the neonate by enabling a greater thermogenic response via shivering.
Clarke
L
L
Department of Biochemistry and Physiology, School of Animal and Microbial Sciences, University of Reading, Whiteknights, United Kingdom.
Darby
C J
CJ
Lomax
M A
MA
Symonds
M E
ME
D002001:Adipose Tissue, Brown / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D001833:Body Temperature Regulation / Q000502:physiology*; D001835:Body Weight / Q000502:physiology; D002245:Carbon Dioxide / Q000097:blood; D002585:Cesarean Section; D004032:Diet; D005260:Female; D006153:Guanosine Diphosphate / Q000378:metabolism; D007453:Iodide Peroxidase / Q000378:metabolism; D008928:Mitochondria / Q000201:enzymology / Q000378:metabolism; D010101:Oxygen Consumption / Q000502:physiology; D011247:Pregnancy; D012756:Sheep; D012768:Shivering / Q000502:physiology; D012890:Sleep / Q000502:physiology; D013696:Temperature; D013963:Thyroid Hormones / Q000097:blood
D013963:Thyroid Hormones; D002245:Carbon Dioxide; D006153:Guanosine Diphosphate; D007453:Iodide Peroxidase