264 



HYPOPHYSIS AND GONADOTROPHIC HORMONES 



tion that initiation of ovarian secretion pre- 

 cedes the capacity to respond morphologi- 

 cally to gonadotrophins has not yet been 

 substantiated by experimental evidence. 



Under normal circmiistances, it is pos- 

 sible that gonadal maturation is brought 

 about by the elaboration of gradually in- 

 creasing amounts of pituitary gonadotro- 

 phins, primarily FSH, or by a gradual in- 

 crease in competence of the gonads to 

 respond to gonadotrophins already present 

 even in immaturity. It is tempting to sur- 

 mise that the gonads of the immature ani- 

 mal elaborate sufficient steroid to suppress 

 the development of gonadotrophic func- 

 tions. There is some evidence that this may 

 be true in females but the situation is less 

 clear in males. Gonadectomy at birth, as 

 Clark (1935b I has shown, leads quickly to 

 an increase in pituitary gonadotrophic po- 

 tency in females but not in males. The 

 mechanism which sustains immaturity may 

 therefore not be the same in the two sexes. 



Despite the apparent refractoriness of 

 infantile ovaries to gonadotrophins of ex- 

 ogenous origin, they respond readily to ex- 

 cessive endogenous gonadotrophins. Thus, 

 ovaries of newborn rats transplanted to the 

 anterior ocular chambers of spayed adult 

 rats respond quickly as shown by an increase 

 in size, follicle maturation, and ovulation, 

 and by the re-establishment of cyclic estrus 

 in the host (Dunham, Watts and Adair, 

 1941). Ovaries which would not normally 

 mature until 45 to 70 days of age were func- 

 tional as grafts at 10 to 20 days of age. This 

 hastening of maturity was not influenced by 

 the period between spaying and grafting, i.e., 

 grafting at the time of spaying was just as 

 effective as grafting at a later time. 



It is pertinent that considerable advance- 

 ment of sexual maturation was seen by 

 Greep and Chester Jones (1950b) in rats in 

 which the ovaries were removed on the 26th 

 day of life and grafted into the neck. These 

 young animals exhibited opening of the 

 vaginal membrane and vaginal estrus within 

 5 to 10 days. In this strain of rats vaginal 

 patency normally appears at about 55 days 

 of age. It was assumed that in the interval 

 before circulation was re-established in the 

 graft the i)ituitary had increased its secre- 

 tion of gonadotrophins as it is known to do 

 when "lonadal secretions are (>liniinate(l or 



rendered ineffective. The revascularized 

 ovaries responded precociously to this 

 heightened pituitary stimulation. Although 

 ]Mandl and Zuckerman (1951 1 were not able 

 to confirm these findings, it is to be noted 

 that the vaginas in their control rats opened 

 at a mean age of 37 days, which allows small 

 latitude for demonstrating a hastening of 

 vaginal opening by this procedure. Many 

 workers have seen precocious vaginal estrus 

 in immature female parabionts following 

 gonadectomy of their partners (for review 

 see Finerty, 1952» and an increase in blood 

 level of FSH has been detected in rats 7 

 days after spaying (Cozens and Nelson, 

 1958). It is evident, therefore, that the pi- 

 tiiitaries and gonads are in delicate hor- 

 monal balance through the period of imma- 

 turity, any disruption of which leads quickly 

 to alteration of the endocrine state. 



B. PUBERTY AND MATURITY 



Puberty is characterized by comj^lex in- 

 teractions between the gonadotrophins and 

 the sex steroids. These become particularly 

 evident in the cyclical episodes in the life 

 of the mature female (Young and Yerkes, 

 1943). Experiments which have attempted 

 to unravel these basic pituitary-gonadal in- 

 terrelationships and the mechanisms re- 

 sponsible for cyclic gonadal functions have 

 involved, as one method of attack, the in- 

 jection of steroid hormones into intact 

 ])ubertal or adult female mammals. 



The influence of the steroid hormones, es- 

 pecially that of the gonadal hormones and 

 their congeners, on the pituitary has been 

 extensively studied. The great variety of 

 experimental procedures employed in these 

 studies has not negated their importance, 

 but it has made comparison of results for 

 a given steroid or between different steroids 

 more difficult and of less validity than might 

 otherwise have been the case. Van Dyke 

 (1939) and Burrows (1949) have provided 

 comprehensive reviews of these data. It will 

 serve the purpose here to examine recent 

 studies wherein a more discriminatory 

 methodology has been employed. These will 

 illustrate tlie major ai^proaches and re- 

 capitulate earlier findings. 



When any steroid, natural or synthetic, 

 endogenous or exogenous, acts on the pitui- 

 tarv. the alternatives ai'c that its function 



