Abstract
The activity of Na+, K+-activatied ATPase or transport ATPase (tATPase) was measured on a cell membrane fraction of the anterior pituitary of male rats. The enzyme activity increased either 2 weeks after thyroidectomy or one week after adrenalectomy. The increased activity was depressed 4 hours after injection of a small amount of T4 (20μg per 100g body weight) or corticosterone (1 mg per 100g body weight), respectively. Similar depres depressive effects were observed with the enzyme preparation from intact animals. Physiologically occurring thyroid hormones, T4, T3 and TA4, depressed the enzyme in vitro. Glucocorticoids, corticosterone, cortisol, cortisone and dexamethasone, were similarly effective in vitro. The effective concentrations of these hormones were as low as 10-8M. In contrast, D-T4, iodide, iodotyrosines, testosterone propionate, estradiol-17β and cholesterol were entirely ineffective. These results indicate that rat anterior pituitary tATPase is one of the target enzymes of the thyroid and adrenocortical hormones. The enzyme is directly and specifically depressed by these hormones.
These findings were discussed in relation to the mechanisms of the feedback regulation of anterior pituitary functions by the thyroid or adrenal cortex.
