Mechanisms regulating the menstrual cycle in women.

Use of the principles and methods of systems analysis in order to know more about normal reproductive function is discussed. This paper is divided into 4 sections. The first section deals with the events in the early and late proliferative period of the menstrual cycle. The main emphasis is on the relationship between follicle-stimulating hormone (FSH) and estrogens. In the second section evidence is presented which indicates that the rising titer of estrogens is the trigger of the preovulatory luteinizing hormone (LH) release. In the third section studies are discussed that relate to the secretion of progesterone by the corpus luteum and of the duration of the postovulatory period. In the fourth section a short description is given of the manner in which the available physiological information may be incorporated into a model of the menstrual cycle. Finally some results of computer simulation based on this model are described. The major value of such modeling lies in the requirement inherent in the techniques to express explicitly all linkages between the variables under consideration in the model as well as to derive equations that while compatible with the physiological information yield realistic curves in computer simulations. Often such simulation reveals internal inconsistencies that had not been realized or yields new insight into physiological processes. Following the paper is a discussion among scientists emphasizing the usefulness of the dual experimental and analytical approach.