17-BETA-ESTRADIOL COUNTERACTS THE FORMATION OF THE MORE ACIDIC ISOFORMS OF FOLLICLE-STIMULATING-HORMONE AND LUTEINIZING-HORMONE AFTER MENOPAUSE

OBJECTIVE When the gonadotrophin levels increase at midcycle, more bas ic isoforms of FSH and LH appear in the circulation. However, when the se gonadotrophins increase at menopause more acidic forms appear. The present study was done to see whether chronic 17 beta-oestradiol (E(2) ) administration to post-menopausal women could counteract the formati on of the more acidic isoforms after the menopause. DESIGN Serum sampl es were obtained from 16 postmenopausal women, mean age 70 years (rang e 63-84 years), 46-169 days after the subcutaneous insertion of a 20-m g E(2)-implant. FSH, LH and E(2) in the sera were measured with fluoro immunoassays. The median charge and the degree of charge heterogeneity of the FSH and LH isoforms were determined for each serum by electrop horesis in 0.1% agarose suspension. Sera from an age-matched control g roup were analysed in parallel. RESULTS The E(2) levels in the E(2)-tr eated women were 230-570 pmol/I, within the range expected during the midluteal phase of the normal menstrual cycle. The mean serum FSH and LH levels were similar to normal follicular phase FSH and LH levels (8 .6 and 20.8% respectively of the control group). It was estimated that individual serum specimens from both groups contained 20-30 different isoforms for both FSH and LH. The median charges of the isoforms of F SH and LH were more basic in all the E(2)- treated subjects than in th eir corresponding untreated controls. The mean median charge for FSH w as close to the values for the follicular and luteal phases and that f or LH close to that for the luteal phase. In some E(2)-treated women t he isoforms were even more basic with a charge similar to that at the midcycle peak. The degree of charge heterogeneity for the E(2)-treated group was significantly (P < 0.001) larger than for the controls and similar to that during the normal menstrual cycle. CONCLUSION Chronic E(2) administration to post-menopausal women counteracted the formatio n of more acidic isoforms of both FSH and LH after the menopause.