Estrone and Estradiol Levels in the Ovarian Venous Blood from Rats During the Estrous Cycle and Pregnancy*

Abstract

Estrone and estradiol measurements were made in rat ovarian vein plasma by radioimmunoassay using dextran coated charcoal for separation (Hotchkiss and Knobil, unpublished). Separation of the steroids was carried out by subjecting the ether extract of the plasma to phenolic partition and column chromatography (celite microcolumn). During the estrous cycle the estrogen secretion rate varied greatly. During diestrus the secretion rates of E₁ and E₂ were low. They had, however, risen sharply by the morning of proestrus. By 2100–2300 hr on the same day the levels again fell significantly, and then remained low during estrus. Secretion rates of E₁ and E₂ were similar early on Day 3 of pregnancy to the values seen at estrus. On Day 4 significant increases in secretion rates of both E₁ and E₂ were observed the peak secretion of E₁ and E₂ occurring between 1400–1600 hr. Estrogen secretion then dropped again to intermediate values and with minor fluctuations remained essentially unchanged until increases were again observed towards the end of pregnancy. The ratio of E₂/E₁ varied from 1 to 7 throughout estrous cycle and pregnancy. The largest ratios were seen at the maximal rates of secretion.