Follicular fluid stimulation of progesterone secretion: time course, dose-response and effect of inhibiting de novo cholesterol synthesis.

This study extends our previous observations of follicular fluid stimulation of progesterone secretion by granulosa cells from immature porcine antral follicles in vitro. Granulosa cells were incubated with either charcoal-treated fluid from large porcine follicles or serum in TC medium 199. Within minutes of the addition of follicular fluid to the cells, enhanced progesterone secretion was observed. A second, more substantial enhancement of progesterone secretion was observed after an additional incubation of 24 to 48 h. As we were unable to detect significant amounts of progesterone within either freshly collected or incubated cells, follicular fluid appears to stimulate both the synthesis and secretion of progesterone rather than just the secretion of preformed progesterone. Inhibition of de novo cholesterol synthesis with an inhibitor of the conversion of 7-dehydrocholesterol to cholesterol, reduced progesterone secretion by cells incubated with serum to a greater extent than by cells incubated with follicular fluid. These studies suggest that follicular fluid may stimulate both de novo cholesterol synthesis and progesterone synthesis from preformed cholesterol. A dose-response test for follicular fluid stimulation of progesterone secretion indicated that 30% follicular fluid in TC medium 199 was as stimulatory as 50% follicular fluid. Ten percent follicular fluid was not stimulatory by itself, but in combination with 1 microgram of FSH/ml (ovine follicle-stimulating hormone), stimulated progesterone secretion to a greater extent than 30% or 50% follicular fluid alone.