130 A. V. Nai hanoov 



incomplete observations are interpreted to mean that the process of "physio- 

 logical atresia" is inevcrsiblc and that follicles which have reached that stage 

 have three possible fates they can be maintained in that piiase with small 

 doses of l^'SH-containing hormones, they can ovulate in the presence of LH, 

 or they can become physically atretic in its absence. 



If gonadotropic hormones are injected into laying hens, ovulations are 

 stopped and, depending on the dose of hormone injected, the ovary will be 

 slightly stimulated or overstimulatcd. Ovulations will be held in abeyance 

 until in injection which will cause the ovulation of one or more follicles, all 

 of which will iinariably be near normal ovulatory size. These observations 

 are cited as additional evidence for the contention that immature follicles 

 receiving adequate gonadotropic hormone support are incapable of ovulating. 

 Only those follicles which have reached ovulatory size and are too large (or 

 too numerous in cases of superovulations) lo be adequately supplied by 

 gonadotropic hormone are capable of ovulating in response to ovulatory 

 doses of LH. 



While additional work will have to be done, much of the evidence presented 

 for birds appears applicable to mammals. Meanwhile it is impossible to 

 discuss the subject in detail until additional evidence is obtained. 



SUMMARY AND CONCLUSIONS 



Data are presented to show that ovulability of follicles is significantly 

 greater in hypophysectomized hens than it is in normal controls, and that 

 the rale of ovulation increases as the interval from hypophysectomy to LH 

 injection increases. The sensitivity of follicles to l.H is increased in hypo- 

 physectomized hens and is significantly greater 12 hr after operation than 

 at 6 hr. 



While it is never possible lo induce multiple ovulations or to cause ovula- 

 tions ol' immature follicles in inlacl hens not treated with hormones, this can 

 be done consistently in hypophysectomi/ed laying hens. 



On the basis of these data the theory is proposed that ovulation is normally 

 due to non-support of the mature follicle by gonadotropic (FSH-containing) 

 hormones. This hormone withdrawal makes them capable of ovulating if 

 they receive the signal (LH) to do so. 



The theory further proposes that LH acts on the ovulable follicle by causing 

 general or localized ischemia which results in necrosis of the stigma and leads 

 to its eventual rupture. 



Comparative studies on the rate of blood How through mammalian and 

 avian follicles in relation to time of ovulation are being continued. 



REFERENCES 



1. Bergeus, a. C. J. and C. H. Li, Amphibian ovulation /// vitro induced l^y mammalian 



pituitary hormones and progesterone, Eiulociiiiolo}^}' 66, 225, 1960. 



2. Brinkhv, H., Unpublished data, I960. 



