THE GROWTH-PROMOTING HORMONE 



gonadotropic effects of prolan. However, they later with- 

 drew the conclusion that this effect was due to the growth- 

 promoting hormone (Evans, Simpson, and Austin, 1933). 



1. The gonads. — It has been shown repeatedly that, as a 

 result of the administration of a growth-promoting extract, 

 female rats exhibit a greater response relatively (and often in 

 absolute terms) than do males. Evans and Simpson (1931) 

 reported on the manner in which gonadectomy affected the 

 response.'" They concluded that the order of susceptibility 

 was the following: the spayed female, the normal female, the 

 castrated male, and, lastly, the normal male. By itself, this 

 statement suggests that the internal secretions of the gonads 

 antagonize the growth-promoting hormone. Gonadectomy, 

 however, influences the rate of growth and the ultimate size — 

 factors which doubtless also affect the response to the hor- 

 mone. 



If a daily injection of 10-20 rat units of oestrone is given to 

 rats from an age of 3-4 weeks to an age of 1 1-22 weeks, the 

 growth in weight (and to a lesser extent, the growth in bone- 

 length) is inhibited as much as 20-25 per cent. The pituitary 

 body of the injected rats appears normal histologically. If the 

 injections are stopped, rapid growth promptly sets in. The 

 normal growth in weight may occur in rats receiving both 

 oestrone and the growth-promoting hormone (Spencer, 

 D'xAmour, and Gustavson, 1932). In experiments lasting only 

 a few days, Engel (1934) was not able to find any change in 

 the response of rats to growth-promoting hormone, if either 

 oestrone or testicular hormone was also administered. 



The effects on the course of pregnancy and on the young, 

 which may follow the administration of a growth-promoting 

 extract of the pars glandularis, are not necessarily attribut- 

 able to the growth-promoting hormone. They will be dis- 

 cussed in chapter iv. 



'" Also see van Wagenen (1928). 



[97] 



