Influence of thyrotropin-releasing hormone administration at birth on thermoregulation in lambs delivered by cesarean.
OBJECTIVE
We examined the hypothesis that exogenous stimulation with thyrotropin-releasing hormone immediately before umbilical cord clamping can improve thermoregulation in near-term lambs delivered by cesarean.


METHODS
Twin lambs were injected with either saline solution alone (control, n = 12) or thyrotropin-releasing hormone in saline solution (n = 16) and were immediately placed in a warm (30 degrees C; n = 14) or cool (15 degrees C; n = 14) ambient temperature. In vivo measurements of temperature control (colonic temperature, oxygen consumption, and incidence of shivering) were then performed during the first 6 hours after birth, in conjunction with plasma thyroid hormone measurements. Brown adipose tissue was then sampled for measurement of uncoupling protein 1 abundance.


RESULTS
Plasma triiodothyronine concentrations were significantly higher in lambs treated with thyrotropin-releasing hormone than in control lambs between 3 and 6 hours after birth, as were plasma thyroxine concentrations 1 and 5 hours after birth. Delivery temperature had no effect on plasma thyroid hormone concentrations. At 6 hours after birth the abundance of uncoupling protein 1 was higher in lambs treated with thyrotropin-releasing hormone than in control lambs. Lambs treated with thyrotropin-releasing hormone exhibited a lower incidence of shivering than did control lambs between 5 and 6 hours after birth, and an effect of ambient temperature on the incidence of shivering was observed only in the control group. From 3 to 6 hours after birth colonic temperature was significantly higher in cool-delivered lambs treated with thyrotropin-releasing hormone than in the control group. Oxygen consumption was higher in cool-delivered lambs than warm-delivered lambs, but this was not influenced by thyrotropin-releasing hormone. Irrespective of delivery temperature, lambs treated with thyrotropin-releasing hormone possessed more pericardial adipose tissue and hepatic glycogen than did control lambs.


CONCLUSIONS
Thyrotropin-releasing hormone treatment stimulated thyroid hormone secretion in the neonatal lamb and improved thermoregulation during the first 6 hours after birth in near-term lambs delivered by cesarean under cool conditions.
Heasman
L
L
Academic Division of Child Health, University Hospital, Queen's Medical Centre, Nottingham, United Kingdom.
Clarke
L
L
Symonds
M E
ME
D002001:Adipose Tissue, Brown / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D001833:Body Temperature Regulation / Q000187:drug effects*; D002352:Carrier Proteins / Q000378:metabolism; D002585:Cesarean Section; D003080:Cold Temperature; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D006003:Glycogen / Q000378:metabolism; D007473:Ion Channels; D007743:Labor, Obstetric; D008099:Liver / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D024101:Mitochondrial Proteins; D011247:Pregnancy; D012016:Reference Values; D012756:Sheep; D013963:Thyroid Hormones / Q000097:blood / Q000378:metabolism; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D013997:Time Factors; D000071256:Uncoupling Protein 1
D002352:Carrier Proteins; D005230:Fatty Acids, Nonesterified; D007473:Ion Channels; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D013963:Thyroid Hormones; D000071256:Uncoupling Protein 1; D013973:Thyrotropin-Releasing Hormone; D006003:Glycogen