THE PITUITARY AND THE THYROID 



the quantitative assay of the thyrotropic hormone. Row- 

 lands and Parkes (1934) based their assay on the change in 

 weight of the thyroid lobes of female^" guinea pigs weighing 

 200 g. initially. They define as a "unit" the daily dose, ad- 

 ministered once daily for 5 days, which causes sufficient hy- 

 pertrophy of the thyroid lobes so that the latter weigh 60 

 mg. (this is about twice the normal weight). They estimated 

 that the fresh pars glandularis of the ox contained six units. 

 Rowlands and Parkes also studied the relationship between 

 dose and response (weight-change of thyroid). In another 

 report, Heyl and Laqueur (1935) recommended that the 

 quantitative assay of the thyrotropic hormone be based upon 

 the histologic change in the immature guinea pig's thyroid. 

 They were of the opinion that weight-change is an unsatis- 

 factory criterion because it is due to a second substance, act- 

 ing synergistically with that producing histologic signs of 

 thyroid stimulation. 



Other interrelationships or effects of the thyrotropic hormone. 

 — Although Aron and Benoit (1932) reported that large doses 

 of oestrin antagonized the thyrotropic effect of an anterior 

 pituitary extract, this has been denied by other investigators. 

 It is agreed that the injection of oestrin into mice or rats may 

 be followed by histologic signs of lessened secretory activity 

 on the part of the thyroid without markedly interfering with 

 the thyrotropic effect of the pituitary. Therefore, it has been 

 suggested that oestrin interferes with the liberation of thy- 

 rotropic hormone from the pars glandularis. (See Benazzi, 

 1933; Bialet-Laprida, 1933-34; Calatroni, Heyl, Repetti, 

 1934.) Parabiosis between a normal and a thyroidectomized 

 rat or between a normal and a spayed rat is accompanied by 

 no changes in the thyroid (Naiko and Ikonen, 1934). On the 

 other hand, experimental hyperthyroidism may markedly 

 prolong the oestrous cycle (Reiss and Pereny, 1928; Suzue and 



" Some authors consider that the thyroid response is greater in female than in 

 male guinea pigs. 



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