STIMULATORY EFFECT OF GROWTH-HORMONE ON IN-VITRO MATURATION OF BOVINEOOCYTES IS EXERTED THROUGH THE CYCLIC ADENOSINE-3',5'-MONOPHOSPHATE SIGNALING PATHWAY

The aim of this study was to investigate whether the stimulatory effec t of growth hormone (GH) on the in vitro maturation and cumulus expans ion of bovine oocytes is exerted through the cAMP or the tyrosine kina se pathway. Therefore bovine cumulus-oocyte complexes (COCs) were cult ured in Medium 199 without fetal calf serum and gonadotropins, but sup plemented with 100 ng/ml bovine GH (bGH; NIH-GH-B18) with or without 1 0 mu M methyl 2,5-dihydroxycinnamate (erbstatin analogue), a specific tyrosine kinase inhibitor; 100 mu M 2',3'-dideoxyadenosine (DDA), a sp ecific adenylate cyclase inhibitor; or 10 mu M H-89, a specific inhibi tor of cAMP-dependent protein kinase A. Epidermal growth factor (EGF; 20 ng/ml) was added as a positive control for tyrosine kinase activati on, and FSH (0.05 IU/ml) was added as a positive control for cAMP medi ation during in vitro maturation in the absence or presence of the inh ibitors. Culture was performed at 39 degrees C in a humidified atmosph ere with 5% CO2 in air. To assess the effect on nuclear maturation, th e proportion of oocytes in metaphase II stage after 16 h of culture wa s determined using 4,6-diamino-2-phenylindole staining. To determine t he effect on cumulus expansion, the diameter of COCs at the onset and after 24 h of culture was measured. The stimulatory effects of GH on o ocyte maturation and cumulus expansion were blocked by DDA and H-89 (p < 0.01). Similarly, FSH-induced cumulus expansion was abolished by DD A and H-89 (p < 0.05), while DDA did not block either EGF-induced oocy te maturation or cumulus expansion. Erbstatin analogue significantly b locked the stimulation of oocyte maturation and cumulus expansion by E GF (p < 0.02) but did not inhibit GH action on the COCs. It is conclud ed that the stimulatory effect of GH on oocyte maturation and cumulus expansion is mediated by the cAMP signal transduction pathway and not by JAK2 phosphorylation.