Discussions 



185 



of fresh corpora lutea in the ovaries (from 2 to 35). The majority of the animals 

 ovulated a larger number of eggs than expected. In the accompanying table I present 

 data collected more recently. It seems that ovulation can be easily induced in the 

 pregnant rabbits and that about half of the pregnant animals superovulate; that is, 

 ovulate a larger number of eggs than expected. The eggs are perfectly normal as shown 

 by the presence of the first polar body and the second maturation spindle. They are 

 physiologically normal because they can be fertilized either in vitro or after transfer 

 to the fallopian tubes of mated rabbits. When a few pregnant rabbits were bred to 

 males no ovulation occurred. Injection of gonadotropic hormone intraperitoneally 

 into pregnant rats also induces ovulation, but only a small number of eggs were 



Table 1. Induction of Ovulation in the Pregnant Rabbit by 

 Administration of Sheep Pituitary Extract 



Total 

 No. of 

 animals 



No. of 

 animals 

 failed to 



ovulate 



Average No. of 



ovulation spots 



or eggs recovered 



Estrous animals bred 2-3 times 

 Non-pregnant animals intravenous injection of 



28-42 I.U. of pituitary extract 

 Pregnant animals (20-29 day) injection of 28-42 



I.U. of pituitary extract 



51 



42 

 46 



9.3 (2-17) 



9.7 (1-15) 



14.7 (4-31) 



found from a few rats ovulated. You may recall that Burdick and Crump have 

 reported that pregnant mice can be induced to ovulate by injection of chorionic 

 gonadotropin (Endocrinology 48, 273, 1951). I wonder whether the induction of 

 superovulation in the pregnant rabbit could throw some light on the hormonal 

 control of ovulation. 



Chairman Hisaw: Dr. Breneman, would you like to add something to the discussion? 



Dr. W. R. Breneman: I have only one or two points to make relative to Dr. Nalbandov's 

 paper. I like his ideas and in line with his conclusions and also at the suggestion of 

 Dr. Fraps we have been attempting to inhibit one ovulation in hens by the adminis- 

 tration of lithosperm. This material, an extract of the plant Lithospermutn ruderale, 

 will inhibit LH after mixture in vitro and will also inhibit the effect of LH on the 

 testes of chicks in vivo. 



Although Dr. Nalbandov did not point this out, most of you know that egg-laying 

 in the hen usually occurs a little later on each succeeding day. It is possible to anticipate, 

 therefore, the time of an ovulation and make lithosperm injections before ovulation 

 occurs. When an injection is made approximately one hour before the anticipated 

 ovulation, that ovulation is usually inhibited but succeeding ones occur normally. 

 Originally we gave as much as 40 mg of lithosperm intraperitoneally but recently, 

 with improved extracts, we find 1.0 mg is an ample amount to produce inhibition. 

 That is, one ovulation is skipped. 



Follicle growth continues when low dosages are given but is stopped with the high 

 doses. Our current data indicate that it is possible to inhibit FSH in vivo with lithosperm 

 but the dose required to inhibit FSH is many times that which is necessary to inhibit 

 LH. It also requires much more lithosperm to inhibit FSH in vitro than it does LH. 



Dr. S. J. Folley: I want to mention the case of the goat. Unlike what H. H. Cole showed 

 many years ago for the ewe, in the female goat it is frequently possible, by a single 

 injection of PMS, to induce not only ovulation but also estrus during the anestrous 



