Plasma oxytocin during pregnancy and lactation in the cynomolgus monkey

Abstract

Plasma levels of oxytocin were measured during pregnancy and lactation in a group (n=23) of cynomolgus monkeys (Macaca fascicularis). Blood samples were taken biweekly from conscious animals during the last trimester of pregnancy and continuing through 6 weeks of lactation. Oxytocin was measured by a specific and sensitive radioimmunoassay which was developed for this study. The assay was useful for measuring plasma levels of oxytocin since it had excellent sensitivity (~0.3 pg/assay tube) and a 50% displacement level of 5 pg/assay tube. Recovery studies and measurement of serial dilutions of extracted plasma demonstrated that the assay was valid for determination of plasma oxytocin in the cynomolgus monkey. Results showed oxytocin was low throughout pregnancy, peaked on the date of parturition, and returned to baseline during lactation. In samples taken 1 week prepartum, oxytocin was 2.1±0.26 and increased to 22.4±6.7 pg/ml on the date of parturition (mean ±SEM). Oxytocin was also measured in a subgroup of animals (n=7) in which the pregnancies terminated in stillbirth or spontaneous abortion.