Hormonal Regulation of Rat Kidney Transamidinase; Effect of Growth Hormone in the Hypophysectomized Rat1

Transamidinase activities have been demonstrated to be markedly lower in kidneys from hypophysectomized rats, than in kidneys from intact or sham-hypophysectomized rats. Adrenalectomy, thyroidectomy, or castration of the male rat is without any effect on the enzyme activity. Hypophysectomized rats given 3 daily doses of small amounts of growth hormone have greater kidney transamidinase activities than untreated hypophysectomized rats. The administration of a number of other hormones is without any effect on the enzyme activity. The use of the enzyme assay as a sensitive and specific measurement of growth hormone activity is suggested. The role of blood and kidney creatine and food deprivation in the alteration of kidney transamidinase activities was investigated. The loss of enzyme activity in the first 3 days following hypophysectomy can be attributed to food deprivation and the high levels of blood and kidney creatine. Food consumption and blood and kidney creatine of the hypophysectomized rats returned to normal levels within 7 days. After this time the low transamidinase activity is increased only by the administration of growth hormone. A direct hormone action on the synthesis or activation of transamidinase is proposed. (Endocrinology78: 1238, 1966)