624 



VERTEBRATE LIFE AND ORGANIZATION 



Figure 30.9. The effects of hypophysectomy in the rat. A, Normal littermate 

 control; B, littermate hypophysectomized when 36 days of age. Ai, A2 and A^ are thyroids, 

 adrenals and ovaries from normal animal; Bi, B2 and Bs are thyroids, adrenals and 

 ovaries from hypophysectomized animal. Note marked differences in size. ( 1 urner: 

 General Endocrinology.) 



As early as 1860 it was recognized that gigantism was correlated with an 

 enlargement ol the pituitary. A growth-promoting extract of beef pitiii- 

 taries was prepared by Evans and Long in 1921 and pure growth hor- 

 mone was isolated in 1944. This controls general body growth and bone 

 growth and leads to an increase in the amount of cellular protein (Fig. 

 30.10). Overactivity of the pituitary during the growth period leads to 

 very tall, but well-proportioned persons, and imderactivity leads to small 

 persons of normal body proportions, called midgets. After normal growth 

 has been completed, hypersecretion of growth hormone produces acro- 

 megaly, characterized by the thickening of the skin, tongue, lips, nose 

 and ears and by growth of the bones of the hands, feet, jaw and skull. 

 Other bones have lost their ability to respond to growth hormone. A 

 race of hereditarily dwarf mice is known whose pituitaries apparently 

 lack the type of cell which secretes growth hormone. These animals can 

 be induced to grow to normal size by implanting a pituitary from a 

 normal mouse. Growth hormones from different species have been found 

 to differ slightly in their amino acid composition and in their effective- 

 ness. Thus beef growth hormone will cause growth in rats but not in 

 man or monkeys. Growth hormone prepared from human or monkey 

 pituitaries will stimulate growth in man and monkeys. 



