MODULATION OF WATER DIFFUSION DURING GONADOTROPIN-INDUCED OVULATION -NMR MICROSCOPY OF THE OVARIAN FOLLICLE

The preovulatory rat follicle reaches a diameter of 1 mm with no inter nal blood vessels. Nutrient supply to the enclosed oocyte depends sole ly on passive diffusion across the follicular wall and the follicular fluid. Spin-echo and stimulated-echo NMR microscopy experiments were a pplied here for studying modulations in water diffusion during gonadot ropin-induced maturation of perfused rat ovarian follicles (32 degrees C). Two diffusion compartments were observed for the follicular wall. The intracellular water diffusion coefficient, measured at a short di ffusion time (9 ms) was 0.28 x 10(-5) cm(2)/s. Diffusion at long diffu sion times was restricted to 16 mu m, the size of cells in the follicu lar wall, and did not change during maturation. In the follicular flui d a transient 26% decrease in the diffusion coefficient was observed 4 -7 h after gonadotropin stimulation, a change that is bound to affect the metabolic balance of the oocyte before ovulation.