FOLLICULAR MECHANISMS ASSOCIATED WITH 4-VINYLCYCLOHEXENE DIEPOXIDE-INDUCED OVOTOXICITY IN RATS

The mechanism of 4-vinylcyclohexene diepoxide (VCD)-induced oocyte des truction in small preantral follicles of rats and mice has not been el ucidated, This study examined the effects of daily dosing of female ra ts with VCD on protein synthesis and follicle viability, An investigat ion of granulosa cells as a target for VCD was also made, Small preant ral follicles (25 to 100 mu m) isolated from untreated immature rats ( day 28) as well as from rats injected daily for 10 d with VCD (0.57 mm ol/kg, IF) or vehicle control (sesame oil) were incubated for 3, 6, or 10 h in vitro with or without VCD, Viability (trypan blue dye exclusi on) or protein synthesis (H-3-leucine incorporation) in follicles was measured, Large preantral follicles (100 to 250 mu m), isolated oocyte s or granulosa cells from small preantral follicles, hepatocytes, and adrenal cells served as controls, Viability was not compromised in sma ll follicles isolated from untreated or VCD-injected rats, However, fo llowing in vitro incubation of small preantral follicles with VCD, the re was a significant decrease in viability by 6 h, This loss in viabil ity was observed in granulosa cells and was even greater in follicles from dosed as compared with undosed animals, The various cell types we re incubated in vitro with or without VCD for 3 h and the rate of prot ein synthesis was measured by H-3-leucine incorporation during the las t hour of incubation, Incubation of small preantral follicles from unt reated animals with VCD for 3 h produced significant inhibition in the rate of protein synthesis, This effect was reversed and significantly stimulated after 6 and 10 h of incubation with VCD, Follicles from an imals that had been dosed daily with VCD for 10 d demonstrated similar inhibition of protein synthesis following 3 h in vitro incubation wit h VCD; however, unlike those from undosed rats, follicles from dosed r ats did not recover from this inhibition after 6 or 10 h of in vitro i ncubation with VCD, In vitro incubation with VCD stimulated the rate o f protein synthesis in large preantral follicles; however, no effect o n the rate of protein synthesis was observed in isolated oocytes and g ranulosa cells, hepatocytes, or adrenal cells, These observations sugg est that VCD affects follicular viability via an effect on granulosa c ells and that daily dosing of rats with VCD makes small preantral foll icles more susceptible to ovotoxicity by VCD.