Mathematical model of FSH-induced cAMP production in ovarian follicles

During the terminal part of their development, ovarian follicles become tot ally dependent on gonadotropin supply to pursue their growth and maturation . Both gonadotropins, follicle-stimulating hormone (FSH) and luteining horm one (LH), operate mainly through stimulatory G protein-coupled receptors, t heir signal being transduced by the activation of the enzyme adenylyl cycla se and the production of second-messenger cAMP. In this paper, we develop a mathematical model of the dynamics of the coupling between FSH receptor st imulation and cAMP synthesis. This model takes the form of a set of nonline ar, ordinary differential equations that describe the changes in the differ ent states of FSH receptors (free, bound, phosphorylated, and internalized) , coupling efficiency (activated adenylyl cyclase), and cAMP response. Clas sical analysis shows that, in the case of constant FSH signal input, the sy stem converges to a unique, stable equilibrium state, whose properties are here investigated. The system also appears to be robust to nonconstant inpu t. Particular attention is given to the influence of biologically relevant parameters on cAMP dynamics.