THE PITUITARY BODY 



3. The thyroid. — Young female rats which have become 

 dwarfed because of thyroidectomy will grow at a normal rate 

 if growth-promoting hormone is administered (Flower and 

 Evans, 1924). Similarly, female rats, thyroidectomized when 

 adult, respond to growth-promoting hormone both qualita- 

 tively and quantitatively like normal adult female rats 

 (Margitay-Becht and Binder, 1934). Smith, Greenwood, and 

 Foster (1927) reported that the injection of a suspension of 

 fresh thyroid gland of the sheep promoted the growth of the 

 thyroidectomized, but not of the hypophysectomized (or nor- 

 mal) rat. In later experiments. Smith (1933) performed both 

 hypophysectomy and thyro-parathyroidectomy in rats; in 

 such animals the effect of a growth-promoting extract was 

 improved by the addition of thyroid extract to the rats' diet. 

 In hypophysectomized rats, the thyroid glands of which were 

 intact, the injection of both thyroid extract and growth-pro- 

 moting hormone produced no greater rate of growth than did 

 the administration of the growth-promoting hormone alone 

 (Smith, 1930), All these findings suggest the following con- 

 clusions: (i) if failure to grow is due to a complete deficiency 

 of the pituitary secretion, no replacement therapy can be 

 effected by the administration of thyroid extract; (2) if 

 dwarfing occurs as a result of thyroidectomy, it probably is. 

 due to the insufficient secretion of the growth-promoting hor- 

 mone; and (3) the growth-promoting effects of an extract of 

 the pars glandularis may in part depend upon a stimulation 

 of the thyroid gland (conceivably, a growth-promoting ex- 

 tract, free from thyrotropic hormone, would be equally effec- 

 tive in hypophysectomized rats whether or not a thyroidec- 

 tomy had also been performed). 



Lee, Teel, and Gagnon (1929), and Lee and Gagnon (1930) 

 studied the gaseous metabolism of normal rats which had re- 

 ceived injections of growth-promoting extracts over long 

 periods. The respiratory quotient after starvation was the 

 same (0.72) in both the normal and the injected rats. In about 



[98] 



