Progesterone and estradiol in the saliva and plasma during the menstrual cycle

Plasma and salivary progesterone and estradiol were measured throughout nine menstrual cycles and before and after intramuscular injection of progesterone in four women. Mean +/- standard error of the mean (SE) salivary progesterone increased significantly from 238.7 +/- 14.3 pg/ml in the proliferative phase to 475.3 +/- 39.8 pg/ml in the secretory phase (p less than 0.001). There was a highly significant correlation between plasma and salivary progesterone levels throughout the menstrual cycle (r = 0.5841, p = 0.001). The ratio of plasma to salivary progesterone was 6.4 during the proliferative phase and increased to 26.7 during the secretory phase. Free unbound progesterone as determined by equilibrium dialysis gave a mean +/- SE level of 126.8 +/- 6.9 pg/ml during the proliferative phase and increased significantly to 196.8 +/- 18.8 pg/ml during the secretory phase (p less than 0.001). The corresponding levels in the plasma were 88.5 +/- 11.2 pg/ml, which increased significantly to 332.2 +/- 39.2 pg/ml (p less than 0.001). Free progesterone constituted 53.7% and 41.4% of salivary progesterone during the proliferative and secretory phases, respectively, whereas the corresponding percentages in the plasma were 5.8% and 2.6%. Both plasma and salivary progesterone levels increased in a dose-dependent manner after an intramuscular injection of progesterone, with peak levels being attained from 2 to 3 hours after the injection. Salivary estradiol levels were 5 to 18 and 8 to 35 pg/ml in the proliferative and secretory phases, respectively, but showed no correlation with plasma estradiol levels. The findings are discussed in relationship to the origin of salivary progesterone and the potential use of it as an index of ovulation.