EFFECTS OF NICOTINE ON IMPLANTATION IN THE RAT

The effects of nicotine on blastocyst implantation were investigated in the rat. Flushing each uterine horn with a constant force and volume of saline at selected times during pregnancy demonstrated that, in control animals, implantation had progressed sufficiently by 1200 h of Day 5 (Day 0 = day of insemination) to prevent conceptus retrieval. In contrast, in animals receiving twice daily s.c. injections of nicotine (5 mg/kg body weight/injection), blastocysts could be retrieved as late as 2100 h of Day 5. Thus, in nicotine-treated rats, the development of blastocyst attachment sufficient to resist flushing was delayed approximately 9 h. Simultaneous entrance of fertilized ova into the uterine lumen at 1800 h of Day 3 in both control and nicotine-treated animals demonstrated that this delay could not be attributed to altered transport through the oviduct. Associated with the altered time course of implantation in nicotine-treated rats were changes in blastocyst development: the time of zona pellucida loss and the growth of the inner cell mass were delayed. However, the number of blastocysts ultimately implanting in nicotine-treated animals did not differ from that of controls.