244 



HYPOPHYSIS AND GONADOTROPHIC HORMONES 



sida, ]\Ieyer, ^NlcShan and Wisnicky, 1943; 

 Dowling, 1949; ^Vlarden, 1952), including 

 man (Davis and Hellbaum, 1944; Maddock, 

 1954). In the absence of luteinizing hor- 

 mone, a situation insured by removal of the 

 recipient animal's own hypophysis, FSH- 

 stimulated ovaries present the appearance 

 of being a mass of translucent cystic fol- 

 licles. During a normal estrous cycle the 

 number of follicles developing to maturity 

 differs among species, but for any given spe- 

 cies the number is quite constant (Brambell, 

 1956). Inasmuch as the size of the ovaries 

 in the continuous (nonseasonal) breeder re- 

 mains reasonably constant, it follows that 

 the level of FSH stimulation must also be 

 maintained at a similar norm. Follicular en- 

 largement, which is brought about in large 

 measure by the accumulation of antral 

 liquor, occurs at a constant rate for any 

 given species (Hisaw, 1947; Brambell, 

 1956). Accordingly, when ovarian enlarge- 

 ment is induced with increasingly greater 

 dosages of exogenous FSH, the growth of 

 individual follicles is not accelerated but 

 more and more follicles are brought to ma- 

 turity; the number, however, is not pre- 

 cisely proportional to the dose. The simul- 

 taneous development of an excessive num- 

 ber of Graafian follicles is the basis of the 

 many demonstrations of artificially induced 

 superovulation and superfetation in rats 

 (Evans and Simpson, 1940), rabbits 

 (Pincus, 1940; Parkes, 1943), sheep (Zawa- 

 dowsky, 1941; Hammond, Jr., Hammond 

 and Parkes, 1942; Casida, Warwick and 

 Meyer, 1944), and cattle (Dowling, 1949; 

 Hammond, Jr., 1949). The administration 

 of FSH to immature animals hastens the 

 maturation of the ovaries and leads to 

 marked sexual precocity in all mammals 

 tested, including the monkey (Simpson and 

 van Wagenen, 1953) and cattle (Casida, 

 Meyer, McShan and Wisnicky, 1943). In- 

 asmuch as FSH activity may be restricted 

 to the growth of follicles, accelerated pu- 

 berty in the instances noted must have oc- 

 curred in part through the concomitant se- 

 cretion of endogenous gonadotrophins, 

 among which LH would be pi'imarily neces- 

 sary. 



That FSH secretion fluctuates rhythmi- 

 cally during reproductive cycles in sexually 

 mature female mammals is suggested bv the 



evidence of Simpson, van Wagenen and 

 Carter (1956), showing an increase in the 

 level of pituitary FSH content during the 

 follicular phase of the menstrual cycle in 

 monkeys. This is in general agreement with 

 the older literature on other mammals (van 

 Dyke, 1939; Smith, 1939). On the other 

 hand, the possibility that rhythmic fluctua- 

 tion in the secretion of gonadotrophin may 

 not be confined to FSH is discussed below. 



3. Physiologic Effects in Males 



In males FSH acts on the spermiogenic 

 cells in the testes with the same selectivity 

 that it exhibits for germinal tissues in the 

 female gonad. The growth of the testes is 

 predominantly due to FSH and is a re- 

 flection of an increase in the size of the 

 seminiferous tubules and of spermatogenic 

 activity (Greep and Fevold, 1937; Creep, 

 van Dyke and Chow, 1942; Simpson, Li 

 and Evans, 1951). When FSH is adminis- 

 tered to immature male rodents the size of 

 the testes is greatly increased, but an ac- 

 celeration of the appearance of fully formed 

 spermatozoa has not been observed. True 

 sexual precocity in males has not, therefore, 

 been obtained, even when every other as- 

 pect of the reproductive system is fully de- 

 veloped. Nelson (1952) cited evidence for 

 the view that FSH may be responsible only 

 for the proliferation of spermatogonia and 

 primary spermatocytes. He speculates that 

 an androgenic influence may participate in 

 the final stages of spermatogenesis. 



Testes developed under the stimulation 

 of exogenous FSH exhibited no change in 

 the number, appearance, or secretory ac- 

 tivity of the intertubular cells of Leydig 

 (Greep and Fevold, 1937; Greep, van Dyke 

 and Chow, 1942; Simi)son, Li and Evans, 

 1951 ) . The unchanged male accessory sexual 

 structures register clearly the fact that no 

 androgen was produced as a result of the 

 treatment. 



4- I'SII in lielation to Conipeusatorij Gon- 

 adal Responses 



A difl'erence in the responses of male and 

 female gonads to FSH is that under ex- 

 ogenous FSH stimulation the testes do not 

 develop beyond their maximal normal adult 

 size as do the ovaries. It has been noted that 

 tlie sexes also differ in the degree of com- 



