CHEMICAL REGULATORS 401 



they were able to induce lactation in spayed, virgin rabbits, which 

 had developed mammary glands prior to the operation, througii 

 the injection of a substance secured from the anterior pituitary. 

 Some years later 'prolactin was extracted in an im|)uro form which, 

 while not causing development of the mammary gland, nevertheless 

 brought about the onset and continuation of the secretory phase. 

 Prolactin \^^ls effective after castration. 



D. Thyreotropic Hormone. While many investigators have 

 demonstrated a close relationship between the pituitary and the 

 thyroid gland, it was not until 1927 that the pituitary gland of the rat 

 was removed to show that the thyroid is dependent upon this structure 

 for stimulation. In 1933, a purified extract under the name of the 

 thyreotropic hormone was prepared. 



E. Adrenotropic Hormone. It was shown in 1930 that if the 

 anterior lobe of the pituitary is removed in rats atrophy of the cortex 

 of the adrenals follows, although normality may be restored by in- 

 jecting pituitary extracts. Later Houssay and his co-workers showed 

 that the active agent in such experiments is a product of the an- 

 terior lobe, also proving the existence of this adrenotropic principle. 



Most biologists now concede the existence of these five hormones 

 from the anterior lobe of the pituitary gland. Evidence is rapidly 

 accumulating which supports the idea of the existence of three more, 

 F to H. 



F. Blood Sugar-raising Principle. It has been previously 

 shown that the removal of the pancreas results in the appearance 

 of sugar in the urine, that is, experimental diabetes is produced. 

 Overactivity of the pituitary, as acromegaly, for example, is usually 

 associated with hyperglycemia (over the normal amount of sugar in 

 the blood) and glycosuria (sugar in the urine). Furthermore, a nor- 

 mal animal develops the same condition when injected with anterior 

 pituitary extracts. Now, when the hypophysis is removed hypo- 

 glycemia results and the animal is very sensitive to insulin. Also it 

 has been shown that if both the anterior pituitary and the pancreas 

 are removed the experimental diabetes resulting from the loss of the 

 pancreas is greatly decreased. It is apparent, then, that in the 

 absence of the pancreas the anterior pituitary tends not only to 

 increase the blood sugar but also to make the animal sensitive to 

 insulin. This clearly indicates that there is a balance between these 

 two glands. It might be added that extracts of the anterior pitui- 

 tary increase the blood sugar in the absence of the pancreas, thy- 



