HORMONES 



3()S 



Hormones of the anterior pituitary 



The anterior lobe produces six well-recognized hormones, which have 

 been named according to their biological effects. All six have been 

 extensively purified and found to be proteins of relatively low mo- 

 lecular weight. The functions of several have been considered briefly 

 in previous sections of this chapter. Additional properties are listed 

 in Table 11-2. 



One of the most interesting and important of the group is the adreno- 

 corticotropic hormone (ACTH, p. 291). The active protein can be 

 hydrolyzed with pepsin or hydrochloric acid until about half of the 

 peptide bonds have been broken without diminishing the activity. This 

 indicates that the effective substance most probably is a peptide com- 

 posed of far fewer amino acids than the ACTH protein. This peptide 

 has not been isolated in pure form, but partly purified products have 

 been obtained which are reported to have molecular weights in the range 

 1000-2000 and to be much more active than ACTH protein on a weight 

 basis. 



The growth hormone (GH) has the power of stimulating growth, both 

 of the skeleton and soft tissues of the animal body. Normally the long 

 bones are "closed off" at the ends and stop developing shortly after the 

 attainment of sexual maturity. This cessation of bone elongation is 

 probably caused by the sex hormones produced at that time. However, 

 in some cases this does not occur, and the continued production of excess 

 GH, leads to gigantism. Heights of eight and nine feet have occurred 

 in human beings. If extra secretion of GH occurs after full maturity, 

 some parts of the body are still able to grow and others are not. This 

 results in distorted growth, which causes a gorilla-like appearance. This 

 condition is called acromegaly (Fig. 11-5). Conversely, a deficiency of 

 GH causes one type of dwarfism. Such dwarfs have normal intelligence 

 but are physically small, delicately formed, and doll-like. The diabeto- 

 genic activity of the pituitary (p. 325) probably is also the result of 

 GH, or of a substance closely associated with it. 



The lactogenic hormone of the anterior pituitary, sometimes called pro- 

 lactin, is another very interesting substance, not only because it stimulates 

 milk production by mammals, but also because it seems to influence mental 

 attitudes. Its effects have been described by R. G. Hoskins as follows: 



"In addition to its effect on milk production, the anterior-lobe product prolactin 

 has a striking influence on animal behavior. It induces broodinessi in the fowl and 

 modifies the nesting behavior in certain fish (Riddle). Its influence on the instinctual 

 behavior of rats has been studied by Wiesner and Sheard and by Riddle. 



"The method of procedure is to place young female rats in cages with materials for 

 nest building. They are then tested as to the strength of their maternal urge by 



