Evidence for the presence of oxytocin in the corpus luteum of the goat.

Purified acetic acid extracts of corpora lutea (CL) of non-pregnant goats were found to contain substantial amounts of oxytocin (OT) as measured by radioimmunoassay. OT standard and the CL extracts released prostaglandin F2 alpha (PGF2 alpha) from rat isolated uteri in a quantitatively similar manner. Treatment of both OT standard and CL extract with sodium thioglycolate, oxytocin antiserum or oxytocin antagonist abolished this biological activity. Acid extracts of CL of pregnant goat were found to contain approximately 2% of levels during the cycle by day 21 after fertile mating and this had a reduced ability to release PGF2 alpha from rat uterus. It is concluded that both the immunoreactivity and the biological activity of the CL extracts are due to the presence of an oxytocin-like substance and that tissue levels of oxytocin are low in pregnant compared to non-pregnant goats.