Modelling the control of ovulation and polycystic ovary syndrome

The control of ovulation in mammalian species appears to be a highly robust process. The primary mechanism is believed to be competition amongst a group of developing follicles, mediated by a hormonal feedback loop involving in the first instance the pituitary. Successful follicles reach maturity and ovulate, the remainder atrophy and die. A model of this control process has been derived by Lacker and his group. Based on simple qualitative assumptions about the hormonal feedback loop, this is able to reflect many of the basic physiological features of ovulation in mammals. However, a fundamental hypothesis of Lacker's work is that all follicles are identical and respond to hormonal signals in precisely the same way. Not only is this improbable, but it also leads to several aspects of the model which are qualitatively unrealistic, most notable of these is its inability to accurately model the condition known as Polycystic Ovary Syndrome. This common malfunction of the ovulatory control mechanism accounts for up to three-quarters of cases of anovulatory infertility in humans and its understanding is therefore of considerable medical significance. In this paper we extend the analysis of Lacker's model to the case of non-identical follicles; this allows us to obtain behaviour much closer to that observed in PCOS patients and to draw some tentative conclusions about the mechanisms underlying this condition.