EXTRATHYROIDAL ACTIONS OF PITUITARY THYROTROPIN: EFFECTS ON THE CARBOHYDRATE, LIPID AND RESPIRA- TORY METABOLISM OF RAT ADIPOSE TISSUE *

The thesis that pituitary thyrotropin (thyroid-stimulating hormone, TSH) affects multiple facets of intrathyroidal metabolism and that changes in iodine economy may constitute merely one ex-pression of these alterations (1, 2) is supported by many published reports. These are summarized in Table I. Only data derived by the direct ad-dition of TSH to in vitro systems have been tabu-lated since, herein, the possible metabolic adapta-tions to changes in thyroid blood flow need not be considered. The in vitro approach has demonstrated that a variety of the oxidative, assimilative and meta-bolic functions of surviving thyroid tissue are stim-ulated when TSH is introduced into media con-taining serum, or other potential organic sub-strates (3-8) (Table I, A). However, TSH also alters the respiration, hydration, and cytostruc-tural lipids of thyroid tissue even in simple sa-line media (1, 9-12) (Table I, B). The occur-rence of the latter phenomena in the absence of exogenous organic metabolites has prompted the suggestion that TSH primarily initiates a realign-ment of existing intrathyroidal pathways and/or a mobilization of preformed intrathyroidal sub-strates ( 5). In order to find an extrathyroidal counterpart for this postulated sequence, the effects of TSH upon adipose tissue have been examined. The inquiry was stimulated by the suggestions of Engel, Engel and McPherson that the generalized metabolic action of pituitary hormones may mimic their effects upon target glands (13, 14). In th