The influence of gonadotropic hormones on the EGF receptor regulation in the rat ovary.

Ovaries of immature rats are endowed with only a small number of EGF binding sites (59.2 X 10(-15) mol/mg protein). During development from day 20 to 28, the binding capacity increases 2.5 times, while the growth of the ovaries remains small. Treatment with FSH on day 20 advances the EGF binding capacity with a 4-fold increase in the number of binding sites within the first two days. HCG has no or only a slight effect on the EGF binding capacity. The EGF receptor formation after FSH treatment takes place before the ovaries begin to grow rapidly. Accelerated ovarian growth is associated with a decrease of EGF binding capacity reaching values below those of the control animals during the subsequent days. The dissociation constants (KD) of the FSH stimulated receptors and of receptors present during development are found in the order of 2.7 and 8.7 X 10(-9) M. The physiological function of the EGF receptor for ovarian cell proliferation and follicular growth is discussed.