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Summary. Isolated Graafian follicles cultured intact were used as a test-system for the meiosis-inducing action of hormonal preparations and for analysing the mediation of this hormone effect. When enlarged follicles were explanted from rats on the day of pro-oestrus before 14.00 hours, i.e. before the preovulatory lh-surge, the oocytes remained in the dictyate state of meiosis throughout an 18-hr culture period. Completion of the first meiotic division could be induced by addition of lh or prostaglandin E2 to the culture medium, or by microinjection of dibutyryl cyclic AMP into the antrum of the cultured follicle. Addition of hcg or fsh to the culture medium was also effective, though possibly due to lh-like activity present in these preparations. Prostaglandin F2α, at 2·8 × 10−5 m, was only partly effective; prolactin, progesterone, 20α-dihydroprogesterone, oestradiol-17β, linolenic acid and adenosine-5′-monophosphate were completely ineffective. The maturation-inducing action of lh was not blocked by cyanoketone, an inhibitor of steroid synthesis. Addition of lh to the culture medium stimulated the formation of cyclic AMP by the isolated follicles. Exogenous cyclic AMP enhanced protein kinase activity in the supernatant fraction of follicular homogenates. It is proposed that the action of lh on oocyte maturation involves the mediation of the adenyl cyclase/cyclic AMP system and possibly of the prostaglandins. An action of steroids could not thus far be implicated. The experimental model described permits study of the mechanism of the meiosis-inducing action of lh under controlled conditions in vitro.
Tsafriri et al. (Sun,) studied this question.