Biophysical Aspects of Ovulation

From a survey of available information about the physical aspects of mammalian ovulation it is apparent that there is no significant change in intrafollicular pressure in ovulation but that there is a marked increase in distensibility of wall tissue probably associated with a decrease in breaking strength (Fig. 5). Analyses of the mechanics of rupture indicate that a relatively small change in distensibility (strain/stress) can produce an unstable follicle which would rupture at normal intrafollicular pressures. A doubling of distensibility, as was induced in vitro by the action of follicular extracts, could render the “model” follicle unstable (Fig. 22). Larger increases in distensibility in vivo in physiological ovulation (6- to 10-fold increases) have been calculated (Fig. 5). Various lines of evidence suggest that the collagen component of the wall is important to its structural strength and that in ovulation the interfibrillar bonding is interfered with in such a way as to reduce the tension developed when the tissue is stretched (increased distensibility) and to permit increased slippage of the fibrils past one another (increased plasticity). An enzymatic agent is assumed, and a collagenase-like enzyme has been identified in the follicular tissue which appears to be released at ovulation. This activity has not been identified as the same which increases follicular distensibility in vivo. How LH stimulates the synthesis or release of the presumptive ovulatory enzyme is not certain, but the route seems more likely to be through stimulation of steroid secretion than by direct stimulation of enzyme synthesis or release. A currently rational hypothesis of ovarian processes in ovulation is illustrated in Fig. 23. See PDF for Figure All steps are supported weakly to firmly by work cited in the review, and none are contradicted by work ignored, I trust.