Effect of different levels of intracellular cAMP on the in vitro maturation of cattle oocytes and their subsequent development following in vitro fertilization

Serum, gonadotrophins, growth factors, and steroid hormones stimulate the i n vitro maturation (IVM) of competent oocytes, acting, directly or indirect ly, upon the adenylate cyclase pathway to produce the intracellular messeng er, cAMP. The intracellular levels of cAMP in cattle cumulus-oocyte complex es (COC) were manipulated by adding to the collection and maturation media invasive adenylate cyclase (iAC), a toxin produced by the bacterium, Bordet ella pertussis. High concentrations of iAC (1 or 5 mu g/ml) in the maturati on medium inhibited the resumption of meiosis, while low concentrations (0. 1 or 0.01 mu g/ml) resulted in high rates of maturation to the MII stage (9 2.6 +/- 2.5 and 98.5 +/- 1.4% respectively). The same low concentrations of iAC in the maturation medium resulted in rates of development to the blast ocyst stage 8 days post insemination (30.1 +/- 4.2 and 45.1 +/- 3.9%, respe ctively), which were either not different, or significantly better, than th ose obtained after IVM in medium supplemented only with serum and gonadotro phins (36.1 +/- 2.9%). Finally, the addition of 0.1 mu g/ml iAC and 0.5 mM 3-isobutyl 1-methylxanthine (IBMX) in the collection medium significantly i mproved the blastocyst rate when IVM was performed in control medium or med ium supplemented with 0.01 mu g/ml iAC (31.9 +/- 5.5 vs. 12.1 +/- 1.6 and 4 5.5 +/- 2.9 vs. 19.1 +/- 2.3% respectively). It is concluded that the maint enance of an optimal intracellular concentration of cAMP before and during IVM ensures a high developmental competence of bovine oocytes matured in me dium without serum and hormones. (C) 1999 Wiley-Liss, Inc.