Sub-lethal effects on offspring of male rats treated with methadone before mating.

We have observed that ingestion of methadone (METH) by male rats prior to mating greatly increased the neonatal death rate of their offspring. In this experiment male rats were allowed drinking water containing METH for 24 hrs, alone or in the presence of females, and then mated with drug-naive females. When both males and females were exposed to METH the frequency of matings was decreased. Offspring of METH males were lighter in weight at birth and at weaning, particularly if their sires had been exposed to females during the period of METH ingestion. Although the neonatal death rate of the METH offspring was more than twice that of controls this difference was not statistically significant. The enhancement of METH effects by concurrent exposure to females leads us to propose that the locus of action of METH is the developing spermatozoa.