The progesterone content of rabbit uterine flushings

Abstract

A detailed study was made of the progesterone [P] content of uterine flushings taken from rabbits of different endocrine states. [One group of rabbits was given human chorionic gonadotropin.] A high content of P was recovered from the uterine lumen of pregnant and pseudopregnant rabbits. The amount of P recovered in the flushings was not simply dependent on the concentration in the plasma, because plasma P concentrations rose before detection of P in the flushings and remained high after uterine P content had fallen. P did not appear in the uterine fluid unless uterine protein was present. This was particularly evident in rabbits treated with P in which, despite abnormally high plasma concentrations, little P was found in uterine fluid until the protein content increased. After treatment of rabbits with estrogen [estradiol] at the time of ovulation, uterine P was present in higher amounts concomitant with an elevation of protein content although the peak values of P and protein were delayed by 2-3 days. Plasma P concentrations of about 5 ng/ml were necessary before P appeared in the uterine lumen.