Endocrinology, Vol 108, 937-942, Copyright © 1981 by Endocrine Society

ARTICLES

Homologous radioimmunoassay for canine thyrotropin: response of normal and x-irradiated dogs to propylthiouracil

WJ Quinlan and S Michaelson

A RIA for canine TSH (cTSH) has been developed using a double antibody method. Rabbit anti-cTSH antisera was slightly cross-reactive with ovine TSH. No evidence of cross-reactivity was noted with human, bovine, rat RSH, or ovine LH. Serum cTSH in euthyroid dogs (9-10 yr of age; 7-14 kg) was 7.0 +/- 0.9 ng/ml (mean +/- SE; range, 2.7-7.9). Normal and x-irradiated (localized to the thyroid or cranium) dogs received 334 mg propylthiouracil (PTU) im in oil daily for 1 week as a goitrogenic challenge. A significant increase (P less than 0.05) in cTSH was noted in normal dogs and in two of four dogs that received 1000 Rads to the thyroid. No significant increase was observed in cTDH in any of the dogs previously given either 100 or 1000 Rads to the head. Although serum T3 and T4 were only slightly decreased (0.10 greater than P less than 0.15 and 0.15 greater than P less than 0.20, respectively) in thyroid-irradiated dogs, a significant decrease (P less than 0.01) in T3 was observed in both normal and x-irradiated dogs maintained on PTU for 1 week. The inability of head x-irradiated cTSH, suggests that moderate to high doses of x-irradiation can impair the ability of the hypothalamic-hypophysial-thyroid axis to respond to a goitrogenic challenge.