Thyrotropin and prolactin response to ambient temperature in newborn infants.

Plasma TSH and PRL level was measured by RIA in 8 full-term newborn infants with mean birth weight of 3420 g (range 3000-4100 g) and mean gestational age of 39.0 weeks (range 38-40 weeks) at postnatal age of 3-4 days. Determinations were performed at neutral thermal environment (32 degrees C) and after 1 h exposure to cold (28 degrees C) and warm (37 degrees C) environment. In response to cold challenge, TSH and PRL increased significantly from 4.17 +/- 0.28 mU/1 and 4625 +/- mU/1 to 4.76 +/- 0.21 mU/1 (p less than 0.01) and 5975 +/- 944 mU/1 (p less than 0.05), respectively. When the newborns were placed in warm environment, both TSH and PRL fell significantly to 3.52 +/- 0.4 mU/1 (p less than 0.05) and 3318 +/- 759 mU/1 (p less than 0.05), respectively. A weakly significant positive correlation was found between TSH and PRL levels suggesting that thermal stress in the newborn results in similar alterations in TSH and PRL, presumably through the same central mechanism.