1 84 Discussions 



I must say that I am pleased that the site of effective lesions in our rats is in the same 

 general area as the tumors associated with precocious puberty in humans. On the 

 other hand, the fmdings raise important questions about the mechanism involved 

 in the early onset of cycling in the experimental animals. Dr. Harris mentioned this 

 morning, and 1 would like to emphasize it again, the possibility that the effects of 

 these lesions are not due to interruption of some sort of inhibitory mechanism, but 

 possibly the lesions are stimulatory in themselves. We know that the arcuate nucleus 

 is involved in the regulation of gonadotropin secretion in the adult rat. Is it possible, 

 therefore, that irritation around lesions destroying only part of this nucleus in immature 

 animals stimulates the adjacent intact portions? Another unsettled question is why 

 hypothalamic lesions are effective only in female animals. These are problems which 

 can only be answered by future research. 



M. C. Chang: I should like first to express my sincere thanks to our hosts for the invitation 

 and to congratulate the previous speakers. Dr. Nalbandov presented beautiful photo- 

 graphs and interesting results on which I can only express my admiration. Then he 

 concluded with the provocative idea that "ovulation is normally a process of physio- 

 logical atresia which occurs as the result of absence of hormones rather than their 

 presence and is thus comparable to menstruation" and that "LH (or another substance?) 

 produces its effect on ovulation by initiating the process of atresia perhaps by initiating 

 ischemia". It is very important for the progress of science to have theories to work on 

 but I should like to pass a few comments for our discussion: (1) If ovulation occurs 

 as a result of absence of hormones rather than their presence then hypophysectomy, 

 the removal of FSH and LH should induce ovulation. But according to his results, 

 a small amount of LH was still needed. (2) Using hypophysectomized animals to 

 prove or to disprove a particular point is perfectly reasonable, but one must bear in 

 mind that hypophysectomy may increase the threshold of one physiological process 

 or decrease the threshold of another. How far the information obtained from hypo- 

 physectomized animals can be generalized to such an extent as a physiological process 

 of ovulation in an intact animal is worthy of consideration. (3) Follicular atresia and 

 menstruation, I think, are not comparable to ovulation because the former two 

 processes are degenerative and regressive processes while the latter is an active and 

 progressive physiological process. (4) Does ischemia play a part in ovulation? After 

 reading Dr. Nalbandov's abstract, we ligated the left ovarian artery of two rabbits, 

 then gave LH for the induction of ovulation. When examined subsequently the right 

 ovaries were found to have ovulated normally while the left ovaries failed to ovulate. 

 When we ligated the left ovarian artery about two hours before the expected time of 

 ovulation the left ovaries again failed to ovulate. It seems that ovulation requires a 

 normal supply of blood, and perhaps a larger than normal blood supply, at the time 

 of ovulation and that severe ischemia would prevent ovulation rather than initiate 

 ovulation. 



Mr. Hammond gave us an excellent review on the artificial induction of ovulation 

 in sheep and cattle. He mentioned the importance of nutrition in relation to the 

 induction of ovulation. Here I should like to stress the influence not only of nutrition 

 but also of environmental factors. Dr. Fernandez-Cano and I (Amer. J. Physiol. 196, 

 653, 1959) have reported that in the rat following stress, such as brief changes of 

 environmental temperature or reduced atmospheric pressure, there would occur 

 inhibition of estrus and ovulation for a long time, about two to three estrous cycles. 

 It seems to me that for the induction of ovulation by administration of hormones 

 one should pay attention not only to ovulation but also to the proper estrous behavior, 

 the transportation of sperm and eggs, the capacitation of sperm and the fertilization 

 of eggs, and the proper implantation of eggs under the administration of hormones. 

 If any one of these processes is upset by hormonal treatment the fertility of animals 

 hardly can be improved. 



Since this conference is mainly dealing with ovulation I should like to introduce here 

 some results of my own. In 1944 Mr. Hammond, Jr. and I injected two groups of 

 pregnant rabbits with 50 LU. or 500 LU. of HCG and we observed a large number 



