A Relationship between Thyroid Function and a Naturally Occurring Inhibitor of Hypophysial Proteinases.

The protrinases of the pituitary gland have received increasing attention in recent years and much of the work has been directed toward finding a physiological function for the enzymes. Adams and Smith (1) described both peptidase and proteinase activities in the gland. Ellis (2) purified one of the proteinases and described a number of its physical and chemical properties. A peptidasc that cleaves bovine growth hormone at a methionyl bond has also been studied by Ellis (3). Reichert (4) found a difference between mammalian and fish hypophysial proteinases and has suggested that the enzymes possessing an alkaline pH optimum may be characteristic of the mammal. Kobayashi et al. (5) noted a correlation between proteolytic activity of the pituitary gland and testicular growth, suggesting that the enzymes may be involved in release of the gonadotropins. Related to this is the report by Reichert (6) of increased proteolytic activity in the ovary upon gonadotropic stimulation. A substance in serum that inhibits the fragmentation of growth hormone and prolactin has been found. In this communication we wish to present evidence which shows that the concentration of this inhibitor is influenced by the physiological status of the thyroid gland.