Sex steroids in reproductive tract tissues: regulation of estradiol concentrations by progesterone

Estradiol-17j3 (E2) and progesterone (P) were quantified in the reproductive tract tissues and striated muscle of rhesus monkeys and rats. After homogenates of these tissues had been extracted with ether and defatted, E2 and P were isolated by chromatography on Sephadex LH-20 columns and quantified by radioimmunoassay. Rhesus monkeys that had been treated with E2 had signifi-cant elevations of this steroid in the reproductive tract tissues (oviduct and uterus) but not in skeletal muscle. When monkeys were treated with a combination of P and E2 the amount of E2 in the reproductive tract of this species was significantly reduced. Similar results were obtained in rats, i.e., after combined progesterone and estradiol treatment, the tissue levels of E2 were signifi-cantly lower than those in the uteri of animals not given P. The levels of P were significantly higher in the skeletal muscle of rats treated with E2 + P. E2 treatment alone increased the amount of endogenous P found in the uterus of the rat