Follicular fluid stimulation of steroidogenesis in immature granulosa cells in vitro.

Granulosa cells from small (1-2 mm) immature porcine follicles were cultured in monolayer in culture media composed of equal parts of culture medium 199 and either (a) fluid from small follicles, (b) fluid from large (6-12 mm) follicles or (c) adult female porcine serum for 6 days, with or without 100 ng LH and/or 2 microgram FSH/ml. Both basal and gonadotrophin-stimulated progesterone secretion were greater in the presence of fluid from large follicles than in serum, for all 6 days. After 4 days of culture, fluid from small follicles enhanced gonadotrophin-stimulated progesterone secretion over that occurring in serum, but to a lesser extent than fluid from large follicles. These studies suggest the presence of a maturation stimulating molecule(s) in follicular fluid which increases in activity or concentration as the follicles enlarge. This factor may be essential for normal granulosa cell maturation in vivo.