Luteal concentrations of oxytocin decline during early pregnancy in the ewe.

The concentration of oxytocin in ovine corpora lutea dropped during pregnancy from 373 ng/g wet weight on Day 14 to less than 5 ng/g between Day 50 and term. The major decrease occurred before Day 20 after mating. Circulating concentrations of oxytocin also decreased between Days 10 and 15 after mating, and were low in late gestation; however, concentrations of oxytocin in plasma on Days 16 and 17 were raised. Mean luteal concentrations of oxytocin ranged from 730 to 2482 ng/g between Days 8 and 14 of the oestrous cycle in non-pregnant sheep. Secretion of oxytocin by the corpus luteum is thought to be one of the mechanisms leading to luteal regression; therefore loss of oxytocin from the corpora lutea in early gestation may contribute to their maintenance.