Levels of Progesterone in Peripheral Plasma During the Menstrual Cycle of the Rhesus Monkey

Plasma progesterone concentrations throughout the menstrual cycles of 12 normal rhesus monkeys were determined using a competitive protein binding technique for progesterone analysis. During the first 11 days of the cycle peripheral plasma progesterone levels were below 0.5 mμg/ml, rising to a mean of 3–4 mμg/ml between days 11 and 15, remaining at these values for approximately 7 days, then falling to the low levels observed during the early portion of the cycle 3 days before the onset of menstruation. Qualitative and quantitative variations in plasma progesterone concentration between individual menstrual cycles are described as are fluctuations during the luteal phases of individual cycles. (Endocrinology81: 1161, 1967)