PHYSIOLOGY OF ANTERIOR HYPOPHYSIS 



263 



dietary protein for the maintenance of 

 normal reproductive performance and for 

 recovery from the impairments induced by 

 severe protein restriction. Female rats fed 

 a diet containing less than 6 per cent pro- 

 tein showed marked atrophy of the repro- 

 ductive organs, whereas male rats fed pro- 

 tein-free diets showed little impairment of 

 spermatogenesis or loss of testis weight 

 although the accessory sex organs were 

 reduced by 50 per cent. Considerable data 

 are available indicating that protein restric- 

 tion impairs the secretion of gonadotrophin 

 in female rats (Samuels, 1950). Less atten- 

 tion has been paid to pituitary hormone 

 content. Leathem (1958) noted a reduction 

 in total gonadotrophic potency in male rats 

 fed a protein-free diet, whereas Srebnik and 

 Nelson (1957) obtained an approximate 2- 

 fold increase in FSH content with no change 

 in LH. They found also that protein restric- 

 tion did not interfere with increases in pro- 

 duction and release of FSH and LH follow- 

 ing ovariotomy. 



Rabbits are surprisingly resistant to pro- 

 tein depletion. Friedman and Friedman 

 (1940) found that female rabbits main- 

 tained on protein- free diets continued to 

 manifest estrus and their capacity for resti- 

 tution of the gonadotrophic hormone po- 

 tency of the anterior pituitary following 

 ovulation was unimpaired. The relationship 

 of deficiencies in specific amino acids to 

 pituitary gonadotrophic functions have not 

 Ijeen satisfactority elucidated. The conflict- 

 ing eviderite4s^ reviewed by Ershoff (1952). 



IV. Gonadal-Hypophyseal 

 Interrelationships 



The dependence of the gonads on the se- 

 cretions of the anterior lobe of the pituitary 

 has been clearly demonstrated in the mam- 

 mals and, although less well documented, 

 exists for all vertebrates, to a greater or 

 lesser degree. This dependence has brought 

 about the consideration of the adenohy- 

 pophysis as a "master gland," but this des- 

 ignation connotes a degree of independent 

 control over the endocrine function of the 

 gonads and the other so-called target or- 

 gans which is not strictly in accord with 

 the facts. There is strong evidence that each 

 of the target organs is an important factor 



in the determination of the functional level 

 of the hypophysis. The gonads and the pi- 

 tuitary play upon each other toward the 

 achievement of a balance of function, har- 

 monious with the fulfillment of the pro- 

 creative functions of the organism. This 

 reciprocal relationship, long known to endo- 

 crinologists, has been referred to as "nega- 

 tive feed-back" or "push-pull." Variations 

 in these interrelationships coincide with the 

 changing epochs of the life of the individual 

 animal. In the mammals the main phases 

 are immaturity, puberty, maturity, and 

 senescence. During each there are subtleties 

 of interplay between hypophyseal and gon- 

 adal influences. Mention should be made of 

 the fact that these interactions of the hy- 

 pophysis and gonads are in large measure 

 dependent on the permissive conditioning 

 of the internal environment by other glands, 

 but especially b}^ the thyroid and adrenals 

 (see chapters by Albert and by Young on 

 the ovary). 



A. IMMATURITY 



Following birth there is a period during 

 which the ovaries are quite unresponsive to 

 administered gonadotrophins. During this 

 period, extending to about 15 days of age 

 in rats, follicles are present which are in- 

 distinguishable morphologically from others 

 which respond readily at an older age. 

 Although the reason for this ovarian insensi- 

 tiveness to extraneous gonadotrophins dur- 

 ing infancy is unknown, Hisaw and Ast- 

 wood (1942) suggested that there must be 

 ]ihysiologic differences between follicles that 

 are morphologically similar. Zuckerman 

 (1952), on the contrary, believes that the 

 follicles become responsive only after a 

 theca interna has been fully differentiated. 

 Along this same line Hisaw (1947) specu- 

 lated that the secretion of estrogen by the 

 theca is a necessary preliminary to the at- 

 tainment of follicular sensitivity to gonado- 

 trophins. He suggested that estrogen acts 

 on the immature follicle in the manner of 

 an organizer, thus rendering the granulosa 

 competent to respond to FSH. Although 

 there is considerable evidence for a direct 

 action of estrogen on ovarian follicles (dis- 

 cussed more fully on page 268 and in the 

 chapter by Young on the ovary) the assump- 



