Mechanisms Controlling Ovulation of Avian and Mammalian Follicles 123 



of ovulation. Similarly, one can discount the massaging effects of the fimbria 

 as aiding in ovulation since follicles rupture normally in animals in which 

 the fimbriae have been amputated or in which the whole reproductive tract 

 has been removed. Neither can intestinal pressure on the ovaries be called 

 upon as an aid in follicular ruptures since in sheep and rabbits ovulation 

 proceeds normally in exteriorized ovaries not in contact with the gut. 



Rugh (11) and Wright (14) have found that in hypophysectomized frogs 

 follicles can be made to ovulate more readily than in intact frog females 

 (sample responses: 100% ovulation in hypophysectomized females vs. 

 30-40% ovulation in intact control frogs). To Wright this observation 

 suggested the possibility that the pituitary gland, due to unavoidable trauma 

 at the time of hypophysectomy, may release a substance which sensitizes 

 follicles and makes them more susceptible to the effects of ovulation-inducing 

 hormones. Although this sensitizing substance was not identified, it was 

 assumed to be the follicle-stimulating hormone (FSH). In another study 

 Wright (13) confirmed earlier observations that frog ovaries taken from 

 intact females can be made to ovulate in vitro. His data are of interest in 

 view of the discussion to follow. Wright found that, as the amount of frog 

 pituitary tissue added to the vessels containing frog ovaries decreased from 

 two to one and on down to l/16th of one gland, eflftciency of ovulation 

 increased from about 20 to 80%. Wright proposed that this decrease in the 

 efficiency of ovulation could be due to an excess of LH in the vessels contain- 

 ing the higher concentration of pituitary gland tissue. When the concentration 

 of pituitary tissue in the fluid bathing the ovaries was kept constant, efficiency 

 of ovulation gradually increased with time, being 0% at 5 to 10 hr after the 

 start of the in vitro trials and approaching 100% at 24 hr. 



Most recently Bergers and Li (1) showed that ovaries of frogs pretreated 

 with extracts of frog anterior pituitary tissue ovulated in vitro in response 

 to ovine LH (ICSH) or growth hormone with about equal efficiency. 

 However, this is not as great as that obtained with frog pituitary gland 

 extracts. No in vitro ovulations were obtained with either prolactin or FSH. 

 Progesterone was also able to induce in vitro ovulations but the number of 

 eggs shed was below that obtained from the hypophysial hormones. 



Chicken follicles too may ovulate in vitro provided they are exposed to 

 the endogenous hormones for an as yet undetermined minimum time prior 

 to being excised. According to Neher et al. (10), follicles removed one hour 

 prior to normally expected ovulation can ovulate in vitro, while preliminary 

 data (unpublished) suggest that removal 3 to 5 hr prior to expected rupture 

 is not followed by dehiscence. 



In women, follicles are surrounded by a network of reticular fibers and 

 reticular cells which resemble smooth muscle cells without fibrils. In rabbit, 

 pig and sheep follicles, true smooth muscle cells are present either in both 

 the theca interna and the theca externa, or only in one of them but not in 



