Oxytocin-induced facilitation of lordosis behaviour in rats is progesterone-dependent

Oxytocin was administered intracerebroventricularly to ovariectomized female rats and its effect on lordosis was examined. In Experiment 1a, oxytocin (0.17 mU in 4 microliters saline) failed to facilitate lordosis behaviour in animals primed acutely with 10 micrograms estradiol benzoate (EB) and 300 micrograms progesterone (P). In Experiment 1b, however, oxytocin significantly facilitated lordosis in animals primed acutely with 10 micrograms EB and 250 or 200 micrograms P. In Experiments 2a and 2b, oxytocin failed to facilitate lordosis in animals treated acutely with 10 micrograms EB, or chronically with 0.8 micrograms EB daily for eight days prior to testing. These results support the hypothesis that the facilitation of lordosis in ovariectomized rats by centrally-administered oxytocin is progesterone-dependent.