Influence of thyrotropin-releasing hormone administration at birth on thermoregulation in lambs delivered by cesarean

OBJECTIVE: We examined the hypothesis that exogenous stimulation with thyro tropin-releasing hormone immediately before umbilical cord clamping can imp rove thermoregulation in near-term lambs delivered by cesarean. STUDY DESIGN: Twin lambs were injected with either saline solution alone (c ontrol, n = 12) or thyrotropin-releasing hormone in saline solution (n = 16 ) and were immediately placed in a warm (30 degreesC; n = 14) or cool (15 d egreesC; n = 14) ambient temperature. In vivo measurements of temperature c ontrol (colonic temperature, oxy gen consumption, and incidence of shiverin g) were then performed during the first 6 hours after birth, in conjunction with plasma thyroid hormone measurements. Brown adipose tissue was then sa mpled for measurement of uncoupling protein 1 abundance. RESULTS: Plasma triiodothyronine concentrations were significantly higher i n lambs treated with thyrotropin-releasing hormone than in control lambs be tween 3 and 6 hours after birth, as were plasma thyroxine concentrations 1 and 5 hours after birth. Delivery temperature had no effect on plasma thyro id hormone concentrations. At 6 hours after birth the abundance of uncoupli ng protein 1 was higher in lambs treated with thyrotropin-releasing hormone than in control lambs. Lambs treated with thyrotropin-releasing hormone ex hibited 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 aft er birth colonic temperature was significantly higher in cool-delivered lam bs treated with thyrotropin-releasing hormone than in the control group. Ox ygen consumption was higher in cool-delivered lambs than warm-delivered lam bs, but this was not influenced by thyrotropin-releasing hormone. irrespect ive of delivery temperature, lambs treated with thyrotropin-releasing hormo ne possessed more pericardial adipose tissue and hepatic glycogen than did control lambs. CONCLUSION: Thyrotropin-releasing hormone treatment stimulated thyroid horm one secretion in the neonatal lamb and improved thermoregulation during the first 6 hours after birth in near-term lambs delivered by cesarean under c ool conditions.