Total T4 and T3 concentrations are often suppressed in burned patients. To investigate the significance of such changes, we have characterized serum T4 and T3 after full-thickness scald burns (60% body surface under anesthesia) of 270-gm male Sprague-Dawley rats housed in a light:dark cycle of 14:10 hr. Groups (N = 9-15) of BURN, SHAM (anesthesia, fur clipped, no burn) and CON (controls) were sacrificed on postburn days 8 and 14. T4 and T3 (radioimmunoassay), free indices (FT4I and FT3I = respective total T4 or T3 × in vitro charcoal T3 uptake, T3U), and free concentrations (FT4 and FT3 = total T4 or T3 × respective equilibrium dialyzable fraction, T4DF or T3DF) were not different between CON and SHAM. Compared to SHAM, mean T4 and FT4I (by about 48% of respective SHAM means on both days), TT3 (by 36, 43%), and FT3I (by 38, 45%) (days 8, 14) were suppressed in BURN (all p < 0.001). T4DF (both days) and T3DF (day 14) were significantly elevated in BURN, demonstrating a deficit in serum binding, but T3U was not. FT4 (by 26, 22%) and FT3 (by 33, 34%) (day 8, 14) were significantly lower in BURN. On either day, covariance analyses (BURN vs. combined CON+SHAM) correlated FT4I or FT3I with respective FT4 or FT3 (all p < 0.001, slopes not different in BURN vs. CON+SHAM), but the lower FT4I and FT3I in BURN significantly overestimated (all p < 0.001) the depression of respective FT4 and FT3 in BURN. Similarly to patients, burned rats exhibit suppressed circulating total and free T4 and T3 concentrations despite elevated dialyzable (free) fractions of T4 and T3. Because of failure of the T3U to account for this serum binding abnormality, the results are most consistent with a burn-induced circulating inhibitor(s) for binding of T4 and T3, not only to transport proteins but also in vitro charcoal, perhaps similar to inhibitors previously described in the sera of patients with various nonthyroidal illnesses. The thermally traumatized rat appears to be a good model for thyroid changes in burns and other nonthyroidal illness.
|Original language||English (US)|
|Number of pages||6|
|Journal||Journal of Trauma - Injury, Infection and Critical Care|
|State||Published - Oct 1985|
ASJC Scopus subject areas
- Critical Care and Intensive Care Medicine