FOLLICLE-STIMULATING-HORMONE AND GROWTH-HORMONE ACT DIFFERENTLY ON NUCLEAR MATURATION WHILE BOTH ENHANCE DEVELOPMENTAL COMPETENCE OF IN-VITRO MATURED BOVINE OOCYTES

This study was designed to investigate the effect of follicle-stimulat ing hormone (FSH) on nuclear maturation, fertilization, and early embr yonic development of in-vitro-matured bovine oocytes and to find out w hether this effect is exerted through a cyclic adenosine monophosphate (cAMP) signal transduction pathway. In addition the effect of the com bination of FSH and growth hormone (GH) on subsequent cleavage and emb ryo development was studied. Therefore cumulus oocyte complexes were c ultured in the presence of FSH (0.05 IU/ml) and the nuclear stage of t he oocytes was assessed using 4,6-diamino-2-phenyl-indole (DAPI) stain ing either after 16, 20, or 24 hr of in vitro maturation or 18 hr afte r the onset of fertilization. To assess the effect of FSH and the comb ination of FSH and GH added during in vitro maturation on the developm ental capacity of the oocytes, cumulus oocyte complexes were incubated in the presence of either FSH (0.05 IU/ml) or FSH (0.05 IU/ml) plus G H (100 ng/ml) for 22 hr, followed by in vitro fertilization and in vit ro embryo culture. To investigate whether FSH-induced oocyte maturatio n is exerted through the cAMP pathway, cumulus oocyte complexes were c ultured in M199 supplemented with FSH (0.05 IU/ml) and H-89 (10 mu M), a specific inhibitor of cAMP-dependent protein kinase A. After 16 hr of culture, the proportion of oocytes in metaphase II (MII) stage was determined. Cultures with GH and without FSH and H-89 served as contro ls. The percentage of MII oocytes at 16 hr of incubation was significa ntly lower (P < 0.001) in the presence of FSH than in the control grou p, while the number of MII oocytes beyond 20 hr did not differ from th e control group. That points to a transient inhibition of nuclear matu ration by FSH. Opposite to FSH, addition of GH during in vitro maturat ion significantly enhanced the number of MII oocytes after 16 hr of cu lture (P < 0.001), which points to the acceleration of nuclear maturat ion by GH. Addition of FSH during in vitro maturation significantly en hanced the proportion of normal fertilized oocytes, cleaved embryos an d blastocysts (P < 0.001). Similarly, addition of GH during in vitro m aturation significantly enhanced the number of cleaved embryos and bla stocysts (P < 0.001); however, in vitro maturation in the presence of GH and FSH did not result in an extra enhancement of the embryo develo pment. Both the inhibition of nuclear maturation by FSH and its accele ration by GH was completely abolished by H-89. In conclusion, in vitro maturation of bovine oocytes in the presence of FSH retards nuclear m aturation via a cAMP-mediated pathway, while it enhances fertilizabili ty and developmental ability of the oocytes. Supplementation of GH and FSH during in vitro maturation did not result in an extra increase in the number of blastocysts following in vitro fertilization and in vit ro embryo culture. (C) 1998 Wiley-Liss, Inc.