Effects of dibutyryl cyclic AMP on oocyte maturation and ovulation in the perfused rabbit ovary

The involvement of cyclic AMP (cAMP) in mammalian oocyte maturation was assessed using cultures of rabbit cumulus-oocyte complexes and in-vitro perfused rabbit ovaries. Rabbit cumulus-oocyte complexes were cultured in Brackett's medium with or without dibutyryl cyclic AMP ((Bu)₂cAMP) at 10^-3, 10^-4 or 10^-5 M for 4-12 h. At 4 h spontaneous meiotic maturation was significantly inhibited by (Bu)₂cAMP (P < 0.025). With prolonged incubation, spontaneous maturation progressed despite exposure to (Bu)₂cAMP. When ovaries were continuously perfused in vitro for 12 h with (Bu)₂cAMP (10^-3 M) or medium alone, (Bu)₂cAMP stimulated ovarian progesterone production, but did not affect ovulation or maturation of follicular oocytes. When ovaries were perfused in vitro with or without (Bu)₂cAMP (10^-3, 10^-4 or 10^-5 M) for the first 2 h and then transferred to medium without (Bu)₂cAMP for an additional 10 h, ovulation did not occur, but transient exposure to (Bu)₂cAMP stimulated a dose-related increase in maturation of follicular oocytes. Degeneration of follicle-enclosed oocytes and cumulus-oocyte complexes was not affected by exposure to (Bu)₂cAMP. These results suggest that transient, but not continuous, elevation of cAMP after the gonadotrophin surge may be required for the initiation of oocyte maturation.