Norethynodrel administered to adult female rats in a daily dose of 0·2 mg for a period of 22 days did not consistently inhibit ovulation or lead to refusal of the male. Acceptance of the male, however, was not always synchronized with follicular rupture. Fertilization occurred in animals mating at the correct time with respect to ovulation, although fewer eggs were fertilized than in control rats. There was some indication that the passage of the free ova through the oviduct is more susceptible to the action of norethynodrel than are the processes of either ovulation or fertilization.
In animals mating up to 22 days following the cessation of treatment, acceptance of the male was always synchronized with ovulation although the number of fertilized ova was lower than in the controls.