The effect of thyroxine on milk secretion and on the phosphatase of the blood and milk of the lactating cow

Abstract

The concentration of phosphatase in the blood serum of normal men differs very little from one adult individual to another. The same is true of a number of other species though in certain animals, such as the dog, the normal variation between individuals is somewhat wider than in man (see King and Armstrong (1934)). On the other hand, in apparently normal cows of the herd of the National Institute for Research in Dairying, it has been found that while the serum phosphatase of any one individual remains within comparatively narrow limits over a period of months, the values for different cows vary widely. Indeed, the level of phosphatase in the blood serum of some cows has been found to differ from that of others by factors as great as 12. In seeking to account for this curious phenomenon, we were led to consider hyperthyroidism in man, which was found by Kay (1930) to be accompanied by increased serum phosphatase. It occurred to us that a possible explanation of the wide variations in the serum phosphatase levels of different cows might be found in individual differences in thyroid activity, particularly since Scoz and Marangoni (1934) had shown that single injections of thyroxine into dogs lead to considerable transient increases in serum phosphatase. Accordingly we decided to study the changes in serum phosphatase brought about by injecting thyroxine into lactating cows characterized by widely different initial values of serum phosphatase. We considered that if our conjecture was correct, not only should the level of serum phosphatase rise as a result of the injections, but the response should be greatest in those animals whose initial levels were lowest. In view of the well-known relationship between serum phosphatase and the metabolism of calcium and phosphorus, it seemed desirable to study serum calcium and inorganic phosphate concurrently.