500 



PHYSIOLOGY OF GONADS 



son, puberty occurs at the very time when 

 older females are emerging from anestrum. 

 Whereas anestrum is often correlated with 

 season of the year, there are exceptions, 

 notably among dogs, in which the correla- 

 tion is ill defined (Engle, 1946). 



In its shortest form ovarian quiescence 

 lasts for only a few days, probably often 

 without being recognized, between the end 

 of one cycle and the active follicular phase 

 of the next. In the chimpanzee it is thought 

 to be the chief factor in the irregularity of 

 length of the cycle (Young and Yerkes, 

 1943). Rossman and Bartelmez (1946) de- 

 scribed a comparable occurrence in mon- 

 keys. At the other extreme, anestrum may 

 occupy the major part of the year in mones- 

 trous animals that have a very limited 

 breeding season. 



A. THE OVARY IN ANESTRUM 



Generally speaking, depression of ovarian 

 function is most extreme in greatly pro- 

 longed periods of quiescence. In the ferret, 

 Hammond and Marshall (1930) reported 

 that in the anestrous ovary follicles can 

 hardly be recognized with the naked eye, 

 because they remain small and deeply 

 placed. The largest follicles at the "end of 

 the season" averaged 460 /x in diameter 

 whereas a "long time after" the average 

 was only 240 jx, increasing again to 720 yu, 

 at the api^roach of a new season. By con- 

 trast, the largest follicles of animals in full 

 heat ranged between 1220 and 1440 /x. Fol- 

 licle atresia abounds in the anestrous ovary 

 of the 13-lined ground squirrel (Johnson, 

 Foster and Coco, 1933). In sheep, however, 

 follicles of large size may be present at 

 any time during anestrum (Kammlade, 

 Welch, Nalbandov and Norton, 1952). 



Some moderate degree of secretory activ- 

 ity of the ovary is indicated even at the 

 depth of i^rolonged seasonal anestrum (13- 

 lincd ground squirrel, Moore, Simmons, 

 Wells, Zalesky and Nelson, 1934; ferret, 

 Hill and Parkes, 1933; opossum, Risman, 

 1946). Although at this time uterus, vagina, 

 and vulva are small, ovariectomy or hypo- 

 l^hysectomy causes a further reduction. On 

 the other hand, these structures are readily 

 stimulated by injection of estrogens. 



It may be said that low-grade follicular 

 cycles proceed throughout the anestrous 



interval, but whether tliere is any syn- 

 chronization of one follicle with another is 

 unknown. Some insight into this problem 

 is furnished by study of (1) the transition 

 from anestrum to the breeding season, and 

 (2) the closely analogous phenomena of 

 adolescence. In the report by Hammond and 

 Marshall, it was shown that in ferrets dur- 

 ing anestrum and proestrum there is a pro- 

 gressive increase in size of the vulva which 

 directly parallels the diameter of the largest 

 follicles. The absence of overt cyclic change 

 is not surprising in view of the fact that 

 estrus is continuous in this species. In 

 polyestrous animals, on the other hand, it 

 might be expected that during anestrum fol- 

 licle growth and accompanying estrogen se- 

 cretion are cyclic, at least at the approach 

 of puberty or of "the season." Important in- 

 formation on this question has been ob- 

 tained from some of the primates, notably 

 the macaque (Allen, 1927; Hartman, 1932) 

 and the chimpanzee (Zuckerman and Ful- 

 ton, 1934; Schultz and Snyder, 1935). 



Slight transitory reddening of the skin of 

 the perineum ("sex skin") of the monkey 

 may occur at intervals for several months 

 preceding the onset of menses, accompanied 

 by moderate desquamation of vaginal epi- 

 thelium. During the long intervals of amen- 

 orrhea that some individuals exhibit during 

 the summer, there is a tendency toward 

 cyclic vaginal desciuamation (Fig. 8.2). The 

 sex skin of the chimpanzee may begin to 

 swell more than a year before the first 

 menstruation. During the ensuing months 

 the swelling may be irregularly cyclic or 

 continuous. Thus, one may judge that low- 

 grade follicular cycles, accompanied by pe- 

 riodic increases in estrogen secretion, may 

 succeed one another during seasonal or 

 ])repubertal anestrum, but that in certain 

 cases these cycles may overlap to such de- 

 gree that rather continuous estrogen secre- 

 tion takes place. 



B. THE HYPOPHYSIS 



The secretory activity of the anestrous 

 ovary is apparently adequate to prevent 

 "castration" changes in the adenohypoph- 

 ysis, for as shown by Moore, Simmons, 

 \^'ells, Zalesky and Nelson (1934) removal 

 of the ovary of anestrous ground squirrels 

 I'esults in hypertrophy of the hypophysis, 



