Critical evaluation of the radioiodination of follicle-stimulating-and luteinizing hormones by lactoperoxidase and its comparison with chloramine-T classical method

A method is described for the enzymatic radioiodination of human gonadotropins by a system consisting of lactoperoxidase, hydrogen peroxide and Na125I. A comparison witth the clhloramine-T modified technique was done a satisfactory specific activity (100 μCi/μg) of the labeled hormone was obtained with the enzymatic iodination, with much greater immunoreactivity and stability than after chloramine-T. As aqueous polyethylene glycol causes precipitation of antibody-bound peptide hormones with radioactive iodine with little or no precipitation of free hormones, a method of separation was developed and applied to radioimmunoassay of gonadotropins, providing several advantages over te double-antibody precipitation method. It was demonstrated that, in humans, the intravenous administration of synthetic LH-FSH/RH, stimulates the pituitary release of both LH and FSH. Results are reported now for normal women, infused with an acute load of 25μg of synthetic LH/FSH-RH and 8 hours infusion of 100μg, during the mid-follicular and luteal phases. The greatest gonadotropin responsiveness to LH/FSH-RH are found in the luteal phase during acute testing. No differences were noticed during chronic infusion as well as acute post-chronic, performed in both phases of the menstrual cycle. The possible modulating effects of steroidal secretion by the ovaries are discussed. (Author)