Oxytocin in the Corpus Luteum of the Cynomolgus Monkey (Macaca fascicularis)

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Abstract
To determine if oxytocin (OT) is present in cynomolgus monkey corpus luteum, OT was measured by a specific and sensitive [radioimmunoassay] RIA in 13 corpora lutea, ovarian venous plasma on the ipsilateral side and peripheral venous plasma at different stages of the luteal phase. Serial dilution of acetic acid extract of the corpus luteum showed parallelism with standard OT in the RIA. Total content of OT in corpus luteum was 1.9 .+-. 0.5 ng (mean .+-. standard error of the mean [SEM] with a content of 0.4-0.8 ng in early luteal phase, 1.0-6.2 ng in midluteal phase, and 0.4-0.7 ng in late luteal phase. OT concentrations in corpus luteum were 21.0-75.2 ng/g wet wt in early luteal phase, increasing to 34.4-602.5 ng/g in midluteal phase; and declining to 3.4-117.4 ng/g in late luteal phase. OT concentrations/mg protein in the corpus luteum were 0.05-19.6 ng with peak concentrations of 14.7-19.6 ng/mg protein on day 22. Sephadex G-25 column chromatography of the corpus luteum extract revealed a single peak for binding activity similar to that of synthetic OT on the RIA. Ovarian vein blood from the same side as the corpus luteum had a significantly higher OT concentrations of 161.2 .+-. 29.7 pg/ml on days 15-24 than 16.8 .+-. 3.6 pg/ml on days 25-28 (P < 0.01) and peripheral plasma OT levels of 23.2 .+-. 3.4 pg/ml (P < 0.025). OT is present and probably produced by monkey corpus luteum with peak OT concentrations found in midluteal phase. Thus, OT may play a role in primate corpus luteum function.