Rat oocyte maturation in vitro : Relief of cyclic AMP inhibition by gonadotropins

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Abstract
The hormone-independent, spontaneous maturation that rat oocytes undergo in vitro can be inhibited by derivatives of cyclic[c]AMP and inhibitors of cyclic nucleotide phosphodiesterase. This inhibition of maturation was shown to be partially relieved by preparations of ovine and rat luteinizing hormone [LH] or follicle-stimulating hormone [FSH]. The ability of gonadotropins to foster the resumption of maturation in cultures of cAMP-inhibited oocytes suggests that this system is suitable for studies of the hormonal control of oocyte development. The dose and time dependency of the response to gonadotropins was examined to study the role of these hormones in oocyte maturation and to compare this effect to other known responses of the cumulus-oocyte complex. Highly purified preparations of rat gonadotropins were less effective inducers of maturation than the more commonly used, but considerably less purified, preparations of ovine gonadotropins. Almost complete relief of inhibition was observed when the oocytes were exposed to a combination of rat LH and FSH. Oocyte maturation was not influenced by the sex steroids progesterone or 17.beta.-estradiol. cAMP may be involved in the intrafollicular inhibition of oocyte maturation; both gonadotropins may be required for maximal stimulation of the resumption of oocyte meiosis; steroids are not involved in this response to gonadotropins.