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

Abstract

Many enzyme activities which were increased by hydrocortisone were decreased by adrenalectomy. This effect was more apparent with enzymes related to amino acid metabolism than those related to carbohydrate metabolism. The latter, although significantly increased by hydrocortisone, did not show marked decreases after adrenalectomy. Hypophysectomy decreased the activities of many enzyme systems associated with carbohydrate metabolism more drastically than did adrenalectomy. The results with the enzymes related to amino acid metabolism were not as 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 L-thyroxine injections was decreased in magnitude or eliminated after adrenalectomy. This was particularly true for enzymes associated with carbohydrate metabolism. Several enzymes increased by L-thyroxine in intact animals were actually decreased in adrenalectomized rats after this treatment. This was particularly true for serine dehydrase and glutamic–pyruvic transaminase. These results are strongly suggestive of a thyroxine–adrenal interaction in the intact animal. Hypophysectomy had a similar effect on enzyme responses to L-thyroxine, with the exception of glutaminase. Therefore, many of the effects of hypophysectomy may actually be related to a lack of adrenal function. It was observed that the removal of the adrenal had similar effects on responses of enzyme activity after thyroxine treatment, as did pituitary removal. Certain of the enzymes were decreased to a greater extent by hypophysectomy, and others were actually increased in activity after removal of the pituitary. It therefore appears that in many enzyme systems there is a complete requirement for the pituitary and (or) adrenals for a L-thyroxine effect on enzyme activity. In other enzyme systems the dependence appears to occur but does not appear to be complete.