Lack of positive correlation between adenyl cyclase activity and iodide transport in rat thyroids.

Abstract

Adenyl cyclase activity was determined in 9000 X g pellets of thyroid homogenates from a) intact rats that received no medication vs propylthiouracil (PTU) treatment for 20 days; b) untreated hypophysectomized rats vs similar rats injected with TSH (1 U) and PTU (20 mg) daily for 3 days, and c) hypophysectomized rats which were given no TSH or a single dose (1 U) of the hormone. In experiment c), thyroids for enzyme assay were removed 10 or 30–45 min after the injection of TSH. Thyroidal iodide transport was measured by the thyroid—serum radioiodide concentration (T/S) ratio, which averaged 69 vs 219 in the intact and PTU—treated rats, 5.2 vs 185 in untreated hypophysectomized rats and those injected with TSH+ PTU, and 4.4 vs 81 and 5.2 vs 78, respectively, in 2 groups of hypophysectomized rats and similar rats treated with TSH 24 hr before they were killed. In spite of the stimulation of the thyroid by endogenous or exogenous TSH reflected by these marked rises in the T/S ratios, adenyl cyclase activity ...