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Oxytocin, oxytocin-associated neurophysin (neurophysin), prostaglandin F_2α (PGF_2α), and progesterone concentrations were measured in the utero-ovarian vein (UOV) of sheep during the estrous cycle and early pregnancy. On days 13- 16 of the cycle, large pulses of PGF_2α, oxytocin, and neurophysin were measured in samples collected at hourly intervals from the UOV draining a corpus luteum (UOV/CL). Most of the PGF_2α pulses (96.5%) coincided with a pulse of both oxytocin and neurophysin, whereas only 55.6% of oxytocin pulses coincided with a pulse of PGF_2α. Therefore, during luteolysis in sheep, uterine PGF_2α release is closely associated with ovarian oxytocin release, and oxytocin release is unlikely to be dependent upon a uterine PGF_2α stimulus.

During frequent sampling, coincident oxytocin pulses were measured in 1) both UOVs when a CL was present in both ovaries and 2) the jugular …