Is oxytocin of conceptus origin involved in inhibition of luteal regression in early pregnancy in ewes?

ABSTRACT

This study describes the presence in and production by the ovine conceptus of an oxytocin-like peptide during the early stages of development. Oxytocin was measured by radioimmunoassay in ovine conceptuses from days 14 to 30 of pregnancy. Tissue concentrations of oxytocin increased from day 14 (24.8 +/- 5 pg/100 mg) until day 19 (122.9 +/- 52 pg/100 mg) and then decreased (3 +/- 1 pg/100 mg). Oxytocin was released into culture medium by day-15 ovine conceptuses at a rate of 262 +/- 55 pg/24 h. Reverse-phase high-performance liquid chromatography (HPLC) analysis of peptides extracted from a pool of ovine conceptuses was conducted using chromatographic conditions developed to separate oxytocin from other nonapeptides. Radioimmunoassay of HPLC fractions for oxytocin revealed an immunoactive conceptus peptide in a single fraction at the same retention time as chromatographed authentic oxytocin. Radioimmunoassay and chromatographic data therefore suggest that this oxytocin-like peptide is similar, if not identical, to authentic oxytocin. Concentrations of oxytocin in conceptus tissue were maximal during the period of inhibition of luteal regression (days 14-19). It is proposed that conceptus oxytocin is involved in the maintenance of luteal function in early pregnancy.