Insulin alone can lead to a withdrawal of meiotic arrest in the carp oocyte

Meiotic arrest of oocyte in an Indian carp, Labeo rohita Ham. has been foun d for the first time to be withdrawn by insulin only. Addition of insulin t o oocytes in vitro caused germinal vesicle breakdown (GVBD), one of the fir st visual markers to determine initiation of the final maturational process . Under the influence of insulin the germinal vesicle (GV) of the oocyte mi grated towards the animal pole, reached the micropyle and then dissolved (G VBD). By using different concentrations of insulin i.e., 0.063, 0.63, 6.3 a nd 12.6 muM, optimum amount required was found to be 6.3 muM. Induction of GVBD by insulin could be blocked by cycloheximide (Chx), a translation inhi bitor, while actinomycin D (AcD) had no effect suggesting, non-involvement of transcriptional activity in this process. Addition of the maturation-ind ucing steroid 17 alpha ,20 beta -dihydroxy-4-pregnen-3-one (DHP) stimulated (P < 0.01) GVBD of carp oocytes and its combination with insulin showed an additive effect. Gonadotropin (GtH) caused GVBD but its effect was greatly augmented by insulin. Our results demonstrate that not only can insulin al one induce GVBD in carp oocytes, but it also augments the stimulatory effec t of DHP or IGF-I or GtH on GVBD. This information will be important in hor monal manipulation during induced breeding of carp.