Evidence against benefit from replacement doses of thyroid hormones in nonthyroidal illness (NTI): studies using turpentine oil-injected rat.

Sprague-Dawley rats were treated with saline or turpentine oil (5 mu 1/g bw sc at 3-day intervals x3) with or without replacement doses of T4 (0.8 g/100 g bw/day ip) or T3(0.3 microgram/100 g bw/day ip). Injection of turpentine oil to the rat consistently caused a significant reduction in serum total T4, total T3, free T4 index and TSH. Despite marked changes in thyroidal economy in experimental rat, iodothyronine 5'-monodeiodinating activity (MA) in the liver, the kidney and the hearth and the hepatic alpha-glycerophosphate dehydrogenase activity were decreased inconsistently and when decreased, the various enzyme activities were not influenced appreciably by treatment with replacement doses of T4 or T3. Cerebral cortical T4 5-MA was normal or increased in the turpentine oil-injected rat. Dermal T4 5-MA was decreased in the turpentine oil-injected rat and replacement doses of thyroid hormones did not normalize it. Urinary excretion of urea nitrogen was normal in the turpentine oil-injected rat and did not change appreciably after treatment with thyroid hormones. Our data suggest that replacement doses of thyroid hormones are not beneficial to a host with altered thyroid economy during a systemic illness.