A Bioassay for Thyroxine Based on Rat Kidney Transamidinase Activities

Abstract

Kidneys removed from rats 6 weeks after thyroidectomy have been found to have low transamidinase activities which were similar to those found in kidneys from hypophysectomized rats. Injections of growth hormone into thyroidectomized rats or of thyroxine into hypophysectomized rats were without any effect on the low enzyme activities, whereas the injections of growth hormone into hypophysectomized rats or of thyroxine into thyroidectomized rats did have an effect on the low transamidinase activities. Thyroxine is concluded to have a concomitant or prerequisite role in the direct regulation of transamidinase activities by growth hormone. A bioassay for thyroxine based on the transamidinase activities of kidneys from thyroidectomized rats has been developed. (Endocrinology87: 1237, 1970)