MECHANISMS CONTROLLING OVULATION OF 

 AVIAN AND MAMMALIAN FOLLICLES* 



A. V. Nalbandov 

 University of Illinois, Urbana 



It is generally conceded that mature follicles rupture in response to the action 

 of an ovulation-inducing hormone (commonly considered to be the luteinizing 

 hormone, LH), but the mechanism of ovulation remains unknown (7). In 

 many mammals the interval between LH release (or injection) and ovulation 

 is about 10 hr, but the changes which take place in the follicle wall between 

 the time when LH first bathes the follicular cells and the time when these 

 cells part along the stigma and allow the ovum to escape are practically 

 unknown. 



It should be kept in mind that LH release from the pituitary is a relatively 

 sudden event which lasts 30 min in the rat (4), 60 min in the rabbit (5) and 

 26 to 150 min in the chicken (12), and that all protein hormones, and LH is 

 no exception, are destroyed very rapidly after they enter the circulation. Thus, 

 whatever influence LH has on mature follicles causing them to rupture 

 about 10 hr later is of transient nature and is certainly not sustained over 

 the whole interval between LH-release and ovulation. It seems that LH 

 initiates a change which then runs its course and terminates in ovulation. 

 The purpose of this paper is to present data on the ovulability of follicles and 

 to propose a theory of the mechanism of ovulation based on these data. 



Several older theories on the mechanism of ovulation have been summarized 

 and reviewed by Hartman (6). Follicles do not rupture because their "ulti- 

 mate" size has been reached or because the interior pressure of the liquor 

 folliculi bursts the follicular wall. It is known that follicles can continue to 

 grow long past the time when they should normally rupture. Cysts are often 

 many times larger than follicles of ovulatory size and the internal pressure 

 in cysts is much greater than it is in follicles; yet, cysts may persist for weeks 

 or months without rupturing. In pigs, cattle and sheep, follicles become 

 flabby a few hours before ovulation even though there is no visible break 

 in the follicle wall and no detectable oozing of its contents. These facts 

 certainly do not argue in favor of intra-follicular pressure as being the cause 



* Data presented were taken from the Ph.D. Thesis submitted by Howard Opel 

 (University of Illinois), 1960. 



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