Influence of zopiclone on male reproductivity in rats.

The influence of zopiclone, a non-benzodiazepine hypnotic, on male reproductivity and the recovery of the influences were examined in rats since it was found that oral administration of zopiclone to male rats produced sperm death and infertility at doses of 50 mg/kg or more. In the present study, zopiclone was administered orally by gavage at doses of 50 and 250 mg/kg once daily for 6 weeks to male rats of 8 weeks old. The rats were paired with untreated female rats at the end of the 2nd, 4th, and 6th weeks of administration and of the 2nd, 4th, and 6th weeks after termination of the administration. As the results, the copulation rates were 100% in the 50 mg/kg group, but the rate was low in the 250 mg/kg group at the end of the 2nd week of administration. The pregnancy rates of 0% and low motility and morphological abnormalities of the sperm were observed in the zopiclone-treated groups at the end of the 2nd week of administration. In the histological examination of the male reproductive organs, such changes as arrest of spermatogenesis and dilation of the epididymal ducts filled with the sperm were observed in the 250 mg/kg group at the end of the 2nd week of administration. In the recovery observation, the ability to impregnate female rats and the condition of the sperm recovered in the 50 mg/kg group at the end of the 2nd week of recovery. In the most rats of the 250 mg/kg group the ability to impregnate female rats and the condition of the sperm recovered at the end of the 4th and 6th weeks of recovery. However, in some rats of the 250 mg/kg group the ability to impregnate female rats and the condition of the sperm were still not recovered at the end of the 6th week of recovery.