Changes in Plasma Concentrations of Progesterone and Estradiol-17.BETA. in Non-Pregnant and Pregnant Cheetahs (Acinonyx jubatus).

Changes in plasma progesterone and estradiol-17β concentrations in 3 non-pregnant and 2 pregnant cheetahs were determined by radioimmunoassays. Progesterone concentrations in the non-pregnant cheetahs varied between 0.78 and 6.20 ng/ml and exhibited elevations at intervals of 10 to 12 weeks. There was one cheetah (2-year-old) in which plasma estradiol-17β concentrations elevated 1 to 2 weeks prior to the peak plasma progesterone concentrations. In the pregnant cheetahs, plasma progesterone concentrations increased at Day 3, rose to a peak (13 ng/ml) at Day 27, and decreased gradually until the time of birth. Plasma estradiol-17β concentrations in the pregnant cheetah attained a peak value (430 pg/ml) at Day 4 (before copulation), decreased gradually until Day 60 and increased again at Day 66 (409 pg/ml). In an aborted cheetah, the estradiol-17β level showed only a slight increase. These data provide the first assessment of reproductive functions in the female cheetah as monitored by plasma steroid profiles.