EFFECT OF FETAL THYROIDECTOMY ON BROWN ADIPOSE-TISSUE AND THERMOREGULATION IN NEWBORN LAMBS

The effect of fetal thyroidectomy on thermoregulation in newborn lambs was investigated. Seven of 14 lambs born normally at term were thyroi dectomized at Day 127 of gestation, Colonic temperature and oxygen con sumption were measured during non-rapid eye movement sleep 6-45 h afte r birth. All lambs were then killed and perirenal brown adipose tissue was sampled for measurement of thermogenic activity (guanosine diphos phate binding), uncoupling protein and lipid contents. Thyroidectomize d lambs tended to have a mean colonic temperature 2.35 degrees C lower (P = 0.067) than controls and two became hypothermic (i.e. colonic te mperature <35 degrees C). Thyroidectomized lambs exhibited lower rates of oxygen consumption (P = 0.05) and an increased incidence of shiver ing thermogenesis. The perirenal adipose tissue of these lambs had a l ower thermogenic activity (P < 0.01), less uncoupling protein (P < 0.0 1) and higher lipid content (P = 0.072) compared with intact controls. It is concluded that fetal thyroidectomy results in a decreased abili ty of newborn lambs to utilize nonshivering thermogenesis in brown adi pose tissue as well as increasing the incidence of hypothermia, These changes are associated with decreased synthesis of uncoupling protein and functional development of brown adipose tissue in the late gestati on fetus.