THE PITUITARY AND THE THYROID 



after small doses.'' This fact, confirmed by the observations 

 of others, may be related to the endogenous formation of an 

 "antithyrotropic" hormone postulated by Collip and Ander- 

 son.'^ A fraction from the serum of horses previously treated 

 with large doses of thyrotropic hormone not only lowered the 

 basal metabolism of normal rats but also prevented any in- 

 crease of basal metabolism if administered simultaneously 

 with thyrotropic hormone. In the latter case, however, there 

 were anatomical indications of stimulation of the thyroid. 

 Animals rendered resistant by prolonged treatment with 

 thyrotropic hormone or by treatment with "antithyrotropic" 

 principle still reacted promptly to thyroxin; so the effect was 

 considered not to be "antithyroid." Confirmatory observa- 

 tions have been made by others (e.g., Scowen and Spence, 

 1934; and Eitel and Loeser, 1935). 



"Antithyrotropic hormone" can be produced by the hypo- 

 physectomized rat (Collip and Anderson), When it is pre- 

 sumably present in the blood of rats or guinea pigs, the pitui- 

 tary contains little or no thyrotropic hormone (Anderson and 

 Collip, Eitel and Loeser). This "antihormone," however, 

 does not prevent the increased excretion of creatine at- 

 tributed to the thyrotropic hormone (Pugsley and others, 

 1934). Eitel and Loeser injected large doses of thyrotropic 

 hormone repeatedly into the wether. They found that the 

 maximum amount of "antihormone" in the blood was pres- 

 ent in the fourth to fifth week, and that very little was present 

 in the twelfth to thirteenth week; later, when even less "anti- 

 hormone" was present, there was also little histologic evi- 

 dence of stimulation of the animal's thyroid. 



Inasmuch as thyroxin produced as prompt and intense an 

 effect in rats in which the "antihormone" prevented thyro- 

 tropic effects, Collip and Anderson concluded that the action 



" For a description of similar experiments in the rabbit, see Hertz and Kranes 

 (1934)- 



'3 Collip and Anderson (1934-35), and Anderson and Collip (1934). 



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