Circulating concentrations of oxytocin during pregnancy in ewes.

Oxytocin and progesterone were measured radioimmunologically during a control cycle, early pregnancy and during several time courses until term in 4 ewes of a local Maroccan breed of sheep. Oxytocin concentrations increased in a similar matter after day 3-4 of the control cycle or after mating and decreased on days 13-15 of early pregnancy about 2 days earlier than during the oestrous cycle. After days 18-19 of pregnancy oxytocin concentrations remained low until term at concentrations as observed during the non-luteal phase of the oestrous cycle. Contrary progesterone concentrations remained high throughout gestation. Maternal recognition of pregnancy seems to have only a slight effect on the secretion pattern of oxytocin for few days after day 12. The results indicate a similar unknown mechanism during the cycle and early pregnancy for the vanishing oxytocin secretion and perhaps synthesis.