High Performance Liquid Chromatographic Separation of Estradiol-17 α and -17/β in Biological Fluids; Application to Plasma, Milk and Urine of Cows

High-performance liquid chromatography of steroid hormones

Although a considerable amount of work has been carried out in the last ten years in developing methods for the separation of steroids by HPLC, it is still not widespread for the reasons discussed above. There is however no doubt that further developments in HPLC technology, in increasing sensitivity and/or specificity of detection systems, perhaps with microbore columns, may lead to an increase in the use of this powerful analytical procedure as an additional separation method to improve specificity of assay. Solution of the problem of simple interfacing of HPLC systems with mass spectrometers (discussed in another chapter by Games) should further increase the application of HPLC. HPLC is of particular value in providing a means of separating unstable compounds prior to assay by relatively nonspecific quantitation methods. Most steroids do not fall into this category, but the steroid vitamin D and its metabolites do and HPLC has proved in this area to be invaluable (see chapter by Jones & DeLuca). There are a multiplicity of different HPLC systems for the separation of steroids, varying in column type (and manufacturer), solvent composition and method of elution, temperature of elution, etc., and only a few attempts have been made to rationalise these data. It would therefore seem that a fruitful area of future study would be the investigation of computerised systems for the selection and optimisation of HPLC systems for particular steroid separations.

A double antibody radioimmunoassay for free and conjugated estradiol-17 beta in cow's milk

A radioimmunoassay for free estradiol-17 beta, conjugated estradiol-17 beta or total (free + conjugated) estradiol-17 beta in defatted milk of cows is described. Conjugated estradiol-17 beta was hydrolyzed by enzymes of Helix pomatia juice. Estrogens were extracted with dichloromethane; no other purification step was required before radioimmunoassay because of the high specificity of the antiserum. Immunoprecipitation was used to separate bound and free estradiol-17 beta. Concentrations measured were corrected for procedural losses on a per sample basis. The assays were shown to be accurate and specific. The sensitivity was 1.3pg/ml for the assay of free estradiol-17 beta (5ml of milk extracted) and 2.9pg/ml for conjugated or total estradiol-17 beta (2 ml of milk hydrolyzed and extracted). Estrogens were measured in the milk of cyclic cows and in cows stimulated with pregnant mare serum gonadotropin (PMSG). A preovulatory increase was clearly observed. Wether or not the ovary was stimulated by PMSG, concentrations of estrogens were higher and the relative increase during the preovulatory peak was greater for conjugated estradiol-17 beta than for the free form. The assay of conjugated or total estradiol-17 beta in defatted milk should be a practical method for assessing preovulatory growth of follicles in cows.