The Role of Steroids in the Control of Mammalian Ovulation 



47 



The significantly lower number of normal follicles without antra in the 30-day- 

 old rat series is certainly not seen in the 90-day-old rat series. The reduction in 

 corpus luteum number may be due to a reduction in the number of follicles 

 ovulating or to a facilitation of corpus luteum resorption, or, indeed, to a 



Table 3. The State of the Ovaries in Thirty-day-old Rats Receiving Norethynodrel 

 BY Daily Injection rw a Fifteen-day Period 



Underlined values differ significantly from control values. 



Table 4. The State of the Ovaries in Ninety-day-old Rats Receiving Norethynodrel 

 BY Daily Injection in a Fifteen-day Period 



Underlined values differ significantly from control values. 



retention of corpora lutea present at the tim^ the injections were begun. A 

 direct examination of the oviducts for ova could perhaps resolve these 

 possibilities. 



In conclusion, I should like to summarize as follows: (a) a good number 

 of steroid substances give evidence of acting as ovulation inhibitors in the 

 rabbit; (b) except, however, for certain progestational steroids, most of these 

 substances are of low or dubious activity; (c) among the compounds of 

 relatively high potency by subcutaneous injection, there are several in which 

 activity by mouth is apparently absent (e.g. XXIX, LIV) or much less than 

 by the parenteral route (e.g. XLI, LV); (cl) one compound, norethynodrel. 



