INTERACTIONS BETWEEN THE CENTRAL 



NERVOUS SYSTEM AND HORMONES 



INFLUENCING OVULATION* 



Charles H. Sawyer and M. Kawakami 

 Department of Anatomy, University of California, Los Angeles 

 and Veterans Administration Hospital, Long Beach, California 



INTRODUCTION 

 Even before the essential role of pituitary hormones in the process of ovulation 

 was suspected, it was recognized that activation of ovulation in certain species 

 required the nervous stimulation related to coitus. Haighton (1) suggested 

 this as early as 1797, but Heape (2) is generally credited with the discovery 

 of this reflex type of ovulation, which is the rule in rabbits, cats and several 

 other species. After the convincing demonstration of hypophysial involvement 

 in the ovulation process over 30 years ago by Smith and Engle (3) numerous 

 attempts were made to analyze the mechanisms by which the nervous system 

 activates the release of pituitary gonadotropin — not only in the reflex 

 ovulators but also in the more numerous spontaneously ovulating forms. 

 These experiments, involving central and peripheral nerve lesions, pituitary 

 stalk sections, hypophysial transplants, electrical stimulation techniques, 

 neurohumoral stimulants and pharmacological blocking agents, have been 

 reviewed comprehensively by Benoit and Assenmacher (4). 



During the 1920s and early 1930s, the physiology of the ovarian hormones, 

 estrogens and progesterone, was also being elucidated (5). The secretion of 

 these steroids was shown to be under the control of pituitary gonadotropins 

 and the latter, in turn, were visuahzed by several workers, including Moore 

 and Price (6) in 1932, to be influenced by a direct feed-back of target organ 

 steroids to the hypophysis. However, because castration cells did not develop 

 in transplanted pituitary glands, Hohlweg and Junkmann (7) proposed the 

 existence of a hypothalamic "sex center" which controlled the release of 

 pituitary gonadotropins and which was affected by the sex steroids in their 

 feed-back circuit. Recently Flerko and Szentagothai (8) have provided 

 evidence in the rat of a direct antigonadotropic action of ovarian steroids at 

 the hypothalamic level by observing the action of ovarian fragments trans- 

 planted into the region of the paraventricular nuclei. 



* Supported in part by a grant (B-1162) from the National Institutes of Health. 



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