Mechanisms Controlling Ovulation of Avian and Mammalian Follicles 125 



that ovulations induced after hypophysectomy were caused by exogenous 

 hormones rather than by the release of the hen's own LH. Success of treatment 

 was judged either by laid eggs or by the presence of ovulated ova at autopsy 

 which was performed at appropriate times following treatments. 



In the absence of hormonal support the ovary of hypophysectomized hens 

 undergoes extremely rapid atrophy (Table 1 ; compare Figs. 1 and 2). 



Table 1 . Effect of Hypophysectomy on Rate of Follicular Atresia 

 OF Laying Hens 



Attention is called to the fact that atresia begins not with the largest but 

 with the smallest follicles (Table 1, 6 hr). By 12 hr after operation it includes 

 the large follicles, but even by 18 hr the medium-sized follicles are not as 

 hard hit as are the two extreme size classes. By 24 hr after hypophysectomy 

 virtually all follicles of measurable size have become atretic. 



On the basis of these data we know that, in the absence of exogenous 

 hormone support, we can count on an interval of about 12 hr after hypo- 

 physectomy during which most follicles of ovulable size can be caused to 

 ovulate with appropriate exogenous hormonal stimulus. 



We shall first consider experiments in which an ovulating dose of LH was 

 injected into laying hens which were hypophysectomized after lay of the C^ 

 follicle and 18 hr prior to the next anticipated release of their own LH. A 

 single intravenous injection of LH was given to some hens as early as 2 hr, 

 to others as late as 24 hr after hypophysectomy. The results of this experiment 

 proved to be as interesting as they were unexpected. It will be seen (Table 2) 

 that while at 2 hr all hens ovulated only one ovum, at 6 and 12 hr after the 

 operation the majority of hens ovulated two, and in one case even three ova. 

 The changes in the efficiency of ovulation, with increasing time after hypo- 

 physectomy, are further shown in the following comparison : 



Hours after hypophysectomy : 2 3 4 6 12 15 18 24 



Average No. of ovulations/hen: 1.00 1.25 1.25 1.88 1.63 1.38 0.63 0.13 



In the intact laying hen it is not possible to induce more than one ovulation 

 which is always the largest follicle in the ovary. But, in hypophysectomized 



