THE PITUITARY STALK AND OVULATION 



G. W. Harris 



Department of Neiiroendocrinology, Institute of Psychiatry 

 Mauds ley Hospital, London S.E.5, England 



The ripening of an ovarian follicle and its rupture, with discharge of an ovum, 

 is dependent on the secretion of the anterior pituitary gland. Administration 

 of purified follicle-stimulating hormone (FSH) results in follicular enlarge- 

 ment, but such follicles are unable to reach full size or secrete estrogen unless 

 some luteinizing hormone (LH) is also present (39). Ovulation is most 

 effectively produced by administration of FSH with a small amount of LH 

 (ratio about 10 : 1). 



FOLLICULAR GROWTH 



Until recently the central neural factors responsible for regulating the 

 pituitary secretion of FSH had received little attention. Studies of such factors 

 require the use of animals with quiescent ovaries; either immature animals 

 or adult animals with a well-marked anestrous period. 



(i) The Hypothalamus and Development of Puberty 



It was at first thought that the onset of puberty was due to an ageing or 

 maturation process in the endocrine glands concerned. However, Foa (34) 

 showed that ageing of ovarian tissue could not be concerned since the ovaries 

 of immature animals transplanted to mature animals show changes typical 

 of the adult organ; likewise ovaries from a mature animal transplanted to 

 the prepubertal become quiescent and undergo atrophy. After it was realized 

 that the anterior pituitary gland was responsible for ovarian activity, it was 

 found that this gland contained active gonadotropic hormone before the onset 

 of maturity and that the implantation of anterior lobes of immature animals 

 into other immature animals might induce gonadal activity. Further, Harris 

 and Jacobsohn (48) found that pituitary tissue obtained from new-born rats 

 grafted under the hypothalamus of hypophysectomized adult female rats 

 became vascularized by the hypophysial portal vessels, and was capable of 

 supporting full adult reproductive functions. Thus the functional activity 

 of the ovary and anterior pituitary gland in the immature animal does 

 not depend on an intrinsic property of the tissue but on the "environment" 

 in which it is situated. 



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