Effect of thyroid hormones on metabolism. II. The effect of adrenalectomy or hypophysectomy on responses of rat liver enzyme activity to L-thyroxine injection

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Abstract
Many enzyme activities, increased by hydrocortisone, were decreased by adrenalectomy. especially those related to amino acid metabolism. Those related to carbohydrate metabolism, although significantly increased by hydrocortisone, did not show marked decreases after adrenalectomy. Hypophysectomy decreased activities of many enzyme systems related to carbohydrate metabolism more drastically than did adrenalectomy. The results with amino acid enzymes were not so clear. Several of these were decreased to a greater degree after hypophysectomy than after adrenalectomy. In contrast, several enzymes were also increased above the control values after hypophysectomy. Adrenalectomy was particularly efficient in decreasing the activities of several transaminases, and hypophysectomy had a marked effect upon decreasing TPN+-linked enzyme systems. The response of several enzymes to T4 injections was decreased in magnitude or eliminated after adrenalectomy, particularly for enzymes associated with carbohydrate metabolism. Several enzymes increased by T4 in intact animals were actually decreased in adrenalectomized rats after this treatment, especially serine dehydrase and glutamic-pyruvic transaminase. These results suggest a T4-adrenal interaction in the intact animal. Hypophysectomy had a similar effect on enzyme responses to T4, with the exception of glutaminase. Therefore, many of the effects of hypophysectomy may actually be related to a lack of adrenal function. Removal of the adrenal had similar effects on responses of enzyme activity after T4 treatment, as did pituitary removal. Certain of the enzymes were decreased to a greater extent by phyophysectomy, and others were actually increased in activity after removal of the pituitary and (or) adrenals for a T4 effect on enzyme activity. In other enzyme systems the dependence occurs but is not complete.