Abstract
1. In normal rats, plasma PB131I was maintained at the initial level or slightlyelevated during repeated blood collections under ether anesthesia, which wasarbitrarily called “maintenance of plasma PB131I”.
2. Maintenance of plasma PB131I was not related to increased TSH secretion, but seemed to be induced by multiple factors including indirect involvementof normally functioning pituitary gland.
3. Vasopressin preparation failed to induce an increased thyroid activity ofnormal rats, but suppressed it, as assessed by lack of maintenance of plasmaPB131I following injection of vasopressin.
4. The suppressive effect was induced by both Pitressin and synthetic lysinevasopressin. But the former was more potent than the latter.
5. Pitressin injection which caused a thyroidal suppression in normal ratsaugmented TSH action to increase plasma PB131I in hypophysectomized rats.
