Precocious oocyte maturation is induced by an inhibitor of cAMP-dependent protein kinase in the intact golden hamster

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Abstract
The purpose of this investigation was to determine if precocious oocyte maturation could be induced by modulating ovarian cAMP‐dependent protein kinase (PKA) or protein kinase C (PKC) signal transduction pathways in the intact hamster. The following inhibitors and stimulators were injected into the ovarian bursal cavity of the anesthetized hamster: N‐[2‐(p‐bromocinnamylamino)ethyl]‐5‐isoquinolinesulfonamide (H‐89), a relatively selective inhibitor of PKA phosphorylations; a structurally related compound, H‐7, a less potent and selective inhibitor used to alter PKA and PKC pathways; phorbol 12, 13‐didecanoate (PDDβ), an active stimulator of PKC and the inactive analog, 4 α‐phorbol 12, 13‐didecanoate (PDDα); and GF109203x, a potent and selective inhibitor of PKC phosphorylations. The experimental design was to inject the modulator into the bursal cavity of one ovary and control solution of diluent or inactive compound into the contralateral bursal cavity. After 1 hr oocytes were collected and evaluated microscopically for the presence or absence of a germinal vesicle. Only oocytes recovered from H‐89 treated ovaries (>50 μM) showed significantly greater frequency of meiotic resumption. Exposure of ovaries to H‐7 (≤150 μM), PDDβ (≤100 μM), or GF109203x (≤100 μM) did not significantly affect oocyte maturation state. These results suggest that ovarian protein phosphorylations carried out by PKA are necessary for the maintenance of oocyte meiotic arrest in situ.