A radioimmunoassay of oestrone in plasma. Plasma levels of oestrone and oestradiol in oophorectomized Rhesus monkeys during treatment with subcutaneous implants containing oestrone.

A highly specific antiserum to oestrone was used to develop a sensitive radioimmunoassay. Plasma was generally analysed without prior separation of the oestrogens. A small amount of plasma (0.1-0.2 ml) was extracted once with diethyl ether. The above and previously described radioimmunoassays were used to estimate plasma levels of oestrogens in oophorectomized monkeys treated with subcutaneous oestrone implants. Three monkeys received a rod containing 40 mg of oestrone. The rods were kept in place for about one year. The release rates from the rods were calculated. The oestrone plasma levels were initially high (370-500 pg/ml). In about 3 months they had fallen to a level of 50-100 pg/ml which was maintained till the removal of the rods. A rise in the oestradiol plasma levels was also observed. It is concluded that rods are suitable for administration of oestrone.