THE MENSTRUAL CYCLE 



ously, about 1931-1932, to a number of investigators, among 

 them first perhaps Brouha and Simonnet in Paris, then to 

 Leonard, Hisaw and Meyer in Wisconsin, and Moore and 

 Price^ in Chicago. This hypothesis suggests that the cycle is 

 Hke a clockwork in which the pituitary is the driving force 

 and the regulatory escapement is the reciprocal action of 

 ovarian and pituitary hormones (Fig. 21). The pituitary 



ESTRUS 



E5TRU5 



HYPOPHYSIS 



ESTRIN 



Fig. 21. Diagram illustrating the alternation or "push-pull" hypothesis 

 of the ovarian cycle discussed in the text. 



makes the follicles grow, ripens the follicles and eggs, and 

 causes the production of estrogenic hormone. The rising tide 

 of estrogenic hormone thus checks the production of pituitary 

 hormone, which begins to fall off as estrus occurs. The estro- 

 genic hormone is used up, and as it reaches a low ebb, the 

 pituitary, now freed from the repressive action of the ovary, 

 again begins to secrete its gonadotrophic hormone. Up goes 

 the pituitary and then up goes the ovary again, thus getting 

 another cycle under way. This scheme, however, cannot fully 

 explain the cycle. As Lamport has shown, a push-pull action 

 of the two hormones would naturally tend, not to effective 

 cyclic fluctuations of estrogen, but to ever smaller changes 

 approaching equilibrium. We must therefore postulate some 

 other event which occurs from time to time to break the bal- 



2 For a discussion of this theory, see Carl R. Moore and Dorothy Price, 

 "Gonad hormone function." American Journal of Anatomy, vol. 60, pp. 

 13-72, 1932, and Harold Lamport, "Periodic changes in blood estrogen." 

 Endocrinology, vol. 27, pp. 673-680, 1942. 



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