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Abstract Gonadotropin Stimulation of the Expansion of Cumulus Oophori Isolated from Mice: General Conditions for Expansion In Vitro The hormonal stimulation of cumulus expansion (mucification) was studied using oocyte‐cumulus cell complexes isolated from Graafian follicles of C57BL/6J mice. Cumulus expansion was stimulated in vitro with human chorionic gonadotropin (HCG) and highly purified rat follicle stimulating hormone (FSH) in Whitten's medium containing fetal bovine serum (FBS). Highly purified rat luteinizing hormone failed to stimulate cumulus expansion. The 50% maximal stimulating concentration of FSH was found to be about 3–4 ng/ ml. Cumulus expansion was also stimulated by dibutyryl cyclic adenosine monophosphate (DBcAMP), but not by dibutyryl cyclic guanosine monophosphate or butyrate. Neither progesterone, testosterone, nor 17β‐estradiol stimulated cumulus expansion. Expanded cumuli were dispersed by hyaluronidase. The stimulation of cumulus expansion by FSH, HCG or DBcAMP required the presence of FBS. The active component of serum had a molecular weight greater than 10,000 daltons and did not require the association of a steroid for activity. Since DBcAMP does not stimulate cumulus expansion in the absence of FBS, it is suggested that the serum factor(s) is involved after the step of FSH stimulation of cAMP production by the complex. The cumulus does not expand if FSH is added to cultures after seven hours of spontaneous oocyte maturation, when the oocytes are at late metaphase I or early anaphase I of meiosis. Therefore, the changes which occur in the oocytecumulus cell complex during spontaneous oocyte maturation affect the ability of the complex to respond to FSH and bring about the expansion of the cumulus.
John J. Eppig (Sun,) studied this question.