Abstract
We reported in the human newborn that the TSH and T3 increases in serum might be due to extrauterine cooling. To study this we have used the newborn sheep. Five groups were studied. Skin and rectal temps, were monitored, and FFA, T4, and T3 measured in serum.
Group I: (n = 8; mean gest. age: 143 d; mean birth wt. 3.1 kg) delivered into air, 20-22° C., cord cut immediately.
Group II: (n = 9; 143 d; 4.3 kg) delivered into 39° water (60 min) and then room air with cord intact (60 min).
Group III: (n = 4; 144 d; 3.7 kg) delivered into air; cord cutting delayed 60 min.
Group IV: (n = 4; 142 d; 4 kg) same as group II; TRH given at 60 min.
Group V: (n = 4; 142 d; 3.3 kg) same as group II; T3 given at 60 min.
Newborn lambs in room air showed a marked increase in T3 and FFA. T4 increased more slowly. As long as the cord was intact T4, T3 and FFA were unchanged in spite of cooling; after cord cutting T3 and FFA increased. Shivering did not prevent body cooling. TRH caused a delayed (4hr.) increase in T4 and T3. T3 augmented the FFA response and produced a more rapid increase in body temp.
We conclude: 1) cord cutting is the primary stimulus increasing T3 and FFA in the newborn; 2) 60 min. FFA and T3 levels correlate with minimum rectal temp.; 3) T3 potentiates the FFA response; 4) the rapid increase in T3 does not seem to be due to TRH, and may be due to increased T4-T3 conversion.
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Sack, J., Beaudry, M., Delamater, P. et al. THE MECHANISM OF THE T3 RESPONSE TO PARTURITION. Pediatr Res 9, 682 (1975). https://doi.org/10.1203/00006450-197508000-00094
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DOI: https://doi.org/10.1203/00006450-197508000-00094