Immunoassay studies of thyrotropin in rat pituitary glands and serum.

Abstract

A sensitive and specific radioimmunoassay for rat thyrotropin (TSH) has been developed which utilizes 125I-mouse thyrotropic tumor TSH, antibovine TSH serum and USP bovine TSH as a standard. TSH in serum and pituitary homogenates was found in fractions corresponding to those previously shown to contain biological activity after gel filtration on Sephadex G-200. Serum TSH in normal rats after decapitation ranged from 15 to 66 μU/ml. During pentobarbital anesthesia, serum TSH was significantly lower (10–37 /μU/ml). Mean normal rat pituitary TSH content was 44 mU/gland. After 50μg thyroxine (T4) every other day for 14 days, serum TSH became undetectable (<6 μU/ml) in 5 of 7 rats, and pituitary content fell to 25 % of normal. Chronic propylthiouracil (PTU) treatment resulted in a progressive increase in serum TSH over a 12-week period. Pituitary TSH content, however, was below normal after 3 weeks of PTU, but rose progressively thereafter to exceed normal at 12 weeks. Following intravenous administration of t...