The Pituitary Stalk and Ovulation 57 



In considering the sequence of events underlying the onset of puberty, 

 account must be taken of the endocrine status of the immature animal. It is 

 likely that the adenohypophysis and gonads are active, secreting glands in 

 prepubertal forms. The data for this statement have been reviewed in detail 

 by Donovan and Harris (20) and may be summarized as follows: 

 {a) The immature gonad secretes sex hormones, since prepubertal castra- 

 tion in the rat results in regression of the seminal vesicles and penis 

 (15), an increase in pituitary content of gonadotropin (52) and the 

 development of castration cells in the pituitary gland (17). 

 {b) The immature pituitary gland secretes gonadotropic hormones since 

 hypophysectomy in infantile rats results in regression of both ovarian 

 (84) and testicular (83) development, 

 (c) A feed-back action of gonadal hormones on pituitary function is 

 indicated by the fact that castration of one of a pair of infantile rats 

 united in parabiosis leads to precocious puberty in the other (61, 62); 

 this can be prevented by the administration of low doses of gonadal 

 hormone to the castrate partner (13). It is probable that a temporary 

 fall in blood concentration of ovarian hormones, resulting in increased 

 gonadotropin secretion, underiies the precocious puberty seen to 

 follow auto-transplantation of infantile ovaries (74, 40). 

 It seems then that before puberty the anterior pituitary gland and gonads 

 are functionally active but, although capable of maintaining adult repro- 

 ductive function at this time, their activity is restricted to a low level. The 

 fact that a feed-back mechanism of gonadal hormones is present in the 

 immature form implies the existence of some control mechanism regulating 

 gonadal activity at this level. 



In 1956 Donovan and van der Werff ten Bosch (21) reported that vaginal 

 canalization in the rat, which serves as an index of ovarian maturation, 

 occurred significantly earlier in animals with lesions in the anterior hypo- 

 thalamus than in control animals. In a recent report (23) these workers give 

 an account of a study based on over 200 animals divided into the following 

 groups — normals, blank-operated and those with various hypothalamic or 

 preoptic lesions. It was found that lesions placed in the anterior region of the 

 hypothalamus in animals 10-15 days of age will, on the average, advance 

 puberty by 5-7 days. In one experiment 34 blank-operated animals had a 

 mean pubertal age of 43.3 days, whilst 13 rats with hypothalamic lesions had 

 a mean pubertal age of 38.1 days. Lesions in the preoptic region did not 

 hasten the onset of puberty. It is of interest that some of the sexually 

 precocious rats displayed cycles of prolonged estrus, and their ovaries 

 contained no corpora lutea, though others had normal vaginal cycles and 

 were fertile. The effective lesions were found to be situated basally in the 

 hypothalamus immediately behind the optic chiasma. Such lesions did not 

 result in hyperphagia and obesity and did not significantly affect the weight 



