Inhibition of LH-induced and spontaneous meiotic maturation in mouse oocytes by Nα-tosyl-L-lysine chloromethylketone

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Abstract
The effect of Nα‐tosyl‐L‐lysine chloromethylketone (TLCK), an inhibitor of trypsin‐type proteases, on luteinizing hormone (LH)‐induced and spontaneous meiotic maturation and follicular production of cAMP in mice was determined. When follicle‐enclosed mouse oocytes were incubated with LH (1μg/ml), they underwent the breakdown of the germinal vesicle (GVBD). TLCK (0.02–0.5 mM) inhibited LH‐induced GVBD in folliculated oocytes. The concentration (0.5 mM) of TLCK that inhibited LH‐induced GVBD did not significantly suppress LH‐induced cAMP production by follicle cells. The effect of TLCK on spontaneous maturation in cumulus cell‐enclosed and denuded oocytes was also determined. TLCK strongly inhibited spontaneous maturation in denuded oocytes only if it was added to the incubation medium for 1–3 h before oocytes were liberated from the follicular tissue. The inhibition of oocyte maturation by TLCK was significantly greater in cumulus cell‐enclosed oocytes than in denuded oocytes, either with or without preincubation with TLCK. These results suggest that trypsin‐type protease in oocytes participates in the process of meiotic maturation in mouse oocytes.