Role of nitric oxide on mitochondrial biogenesis during the ovarian cycle.

The mitochondrial changes in the ovary during the ovarian cycle are adapted to a cyclically increased-decreased energy demand. In the proliferative phase, the increased energy needs are sustained by the recruitment of mitochondria in active state 3, by an increased tissue O2 consumption and ATP production and by an increase in the number of mitochondria. In the phase of decreased energy needs, mitochondria-dependent apoptosis reduces tissue and mitochondrial O2 uptake. The ovary morphological changes during the cycle describe a process in which the follicles undergo a clear cycle with two sequential phases: proliferation and apoptosis. The follicular growth stimulated by FSH characterizes a tissue that shows a quick cell proliferation. During the ovarian cycle, tissue and mitochondrial O2 uptakes, mitochondrial mass, mitochondrial NO production and cytochrome oxidase activity exhibit a biphasic pattern, with marked increases in the ovary proliferative phases. Relatively low levels of NO seem to drive the cell signaling for follicle proliferation, whereas relatively high NO levels trigger mitochondria-dependent follicle apoptosis.