Local regulation of granulosa cell maturation

Fluid from small antral follicles inhibits several functions of porcine granulosa cells from 3-10-mm follicles in vitro, whereas fluid from large follicles stimulates cells from small follicles. Local factors may be needed in vivo to enable granulosa cells to fully respond to gonadotrophins. Only those follicles containing local stimulators may develop while those containing inhibitors may become arrested in development or become atretic. We have compared the actions of GnRH analogs and chondroitin sulfate (CS) on porcine granulosa cell steroidogenesis with actions of follicular fluids. GnRH agonist mimicked follicular fluid inhibition of progesterone secretion but GnRH antagonist did not antagonize follicular fluid's inhibitory actions. GnRH antagonist mimicked follicular fluid enhancement of basal and LH-stimulated progesterone secretion, but did not mimic follicular fluid enhancement of FSH action or stimulation of estrogen secretion. GnRH agonist blocked the enhancement of LH-stimulated progesterone secretion by both GnRH antagonist and stimulatory follicular fluid. CS inhibited basal and LH-stimulated progesterone secretion but did not inhibit pregnenolone utilization, aromatase activity or estrogen secretion. GnRH-like molecules and CS may be partially responsible for follicular fluid actions on granulosa cells. The actions of other molecules are needed to explain the total effects of follicular fluids on granulosa cells.