EFFECT OF FETAL THYROIDECTOMY ON THE METABOLIC RESPONSE TO BIRTH IN LAMBS

Abstract

The effect of perinatal changes in thyroid function on adaptation at birth as reflected in plasma free fatty acids (FFA's), catecholamines, glycerol and biophysical parameters was assessed in thyroidectomized (TX) (n=5) and sham (n=4) operated (control) fetal sheep. Surgery was done at 133±1 days gestation followed by cesarean delivery at 146±1 days gestation into a room held at 72°F. Measurements were made in utero before delivery and at timed intervals after birth. Blood gases, rectal temperature, pulse, respiratory rate, mean blood pressure, plasma glycerol and plasma norepinephrine levels were similar. Plasma epinephrine levels were markedly elevated after delivery in the TX animals with a mean (±SEM) peak level of 1849±593 pg/ml compared to a mean peak level of 263±129 pg/ml (p<0.01) in controls. FFA's were decreased in the TX animals with lower levels measured at 15 min (237±81 (SEM) μEq/L vs 688±79, p<0.01) and 30 min (439±66 vs 1026±230, p<0.01). T3 increased after delivery in controls (260-360 ng/dl) and was measurable but did not increase after delivery in the TX animals (8-45 ng/dl). Conclusions: 1) thyroid hormones play an important role in non-shivering thermogenesis after birth as reflected in decreased plasma FFA's in the TX animals; 2) altered thyroid status results in an augmented epinephrine response to birth; 3) absence of the perinatal T3 surge does not affect body temperature when the animal is exposed to a mild cold stress.

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