THYROXIN and adrenalin are both known to have a calorigenic effect, manifested by an increase in oxygen consumption (1, 2). Ring (3) showed that the response to adrenalin was potentiated by thyroxin, and that the logarithm of the response was proportional to the basal metabolism. That this was a direct relationship between the two hormones was demonstrated by the inability of non-thyroid metabolic stimulants and depressants, such as dinitrophenol and fasting, to affect the response to adrenalin. Schaeffer and Thibault (4, 5) also found that thyroxin greatly increased the response to adrenalin. The potentiation could be observed even before and after the calorigenic effect of the thyroxin itself was evident. In both investigations single large doses of thyroxin were used. Ring proposed that either a reversible chemical reaction between thyroxin and adrenalin or adsorption may be involved. Recent data on the action of hormones at the enzyme level suggest that adrenalin and thyroxin may influence consecutive rate-limiting reactions, adrenalin by increasing the amount of substrate, i.e., glucose (6, 7), and thyroxin by accelerating the utilization of glucose (8, 9, 10, 11). There is also the possibility that thyroxin prolongs the action of adrenalin by retarding its oxidation by amine oxidase, as thyroxin has been shown to decrease the level of this enzyme (12, 13, 14).
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H. EARTLY (1956) studied this question.