Discussions 



117 



sterile rat, following the "interrupting" dose of progesterone, stores sufficient gonado- 

 tropin to be released on hypothalamic stimulation and cause ovulation. However, 

 ovulation did not occur in any of the progesterone experiments regardless of the 

 dosage employed. This would tend to support the hypothesis that progesterone 

 facilitates ovulation in the rat by its action on the hypothalamus, perhaps in a fashion 

 described by Kawakami and Sawder {Endocrinology 65, 631, 1959) for the rabbit. 



Fig. 8. Effect of daily injections of progesterone on the vaginal cycle of the androgen- 

 sterilized, persistent-estrous rat. 



The data further implicate the anterior regions of the hypothalamus as the specific 

 sites of progesterone action. Thus, prepubertal treatment of rats with androgen may 

 not only render the preoptic areas of the hypothalamus refractory to electrical stimula- 

 tion but to progesterone as well. Further evidence suggesting that progesterone may 

 exert its action at the preoptic area has been presented by Greer {Endocrinology 53, 

 380, 1953) and Van Dyke et al. {Proc. Soc. Exp. Biol. Med. 95, 1, 1956) who reported 

 that rats in which ovulation had been interrupted by anterior hypothalamic lesions 

 would not ovulate in response to progesterone. 



These data, although in contrast to the observation reported by Everett for the 

 normal rat, do support the hypothesis that the preoptic region of the rat may be the 

 critical site for control of ovulation. 



This work was supported by Grant Number RG-5496 from the United States Public 

 Health Service. 



Chairman Nelson: We shall now have a period of general discussion. I think perhaps I 

 would like to call on Dr. Folley to contribute such remarks as he wishes to the dis- 

 cussion this morning. 



Dr. S. John Folley: First, may I say what I should have said yesterday afternoon, when 

 Dr. Creep called on me. I want to express my sincere thanks to the appropriate people 

 who made it possible for me to come all the way from England to be present at this 

 wonderful meeting. It is particularly fortunate that arrangements could be made to 

 hold it in such magnificent surroundings which provide a wellnigh perfect environ- 

 ment for the discussion of a specialized subject by a small group such as this. I regard 

 it as a great privilege to be here. 



