Abstract
Goitres were produced in guinea pigs by administering propylthiouracil (PTU) dissolved in drinking water. It was found that a diurnal pattern of blockade of hormone synthesis and relief from such blockade developed. Evidence presented for thyroid blockade are gland weights of 500 mg or more; for relief from block, high uptake in vitro of 125I −1, formation in vitro of thyroid hormones, and great sensitivity to thyrotropic hormone (TSH). Methods for estimating PTU are described which permit studies of the kinetics of this drug in guinea pigs and mice. Guinea pigs do not develop tolerance to PTU. The t 1 2 for a single oral dose was 7.5 ± 1.5 hr; after 3 months of daily intake of PTU, another t 1 2 estimate gave 6.2 ± 1.3 hr. In mice, at least two phases (0.5 and 2.7 hr) in the disappearance of i.v. PTU were found. Several unidentified metabolites could be shown in guinea-pig tissues. The ratio of the radioactivities of bile and serum after a single oral dose of 35S-PTU was greater than 10 : 1. As bile did not contain any unchanged PTU, guinea-pig liver appears to metabolize PTU rapidly.
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