DETECTION OF DIMERIC INHIBIN THROUGHOUT THE HUMAN MENSTRUAL-CYCLE BY 2-SITE ENZYME-IMMUNOASSAY

OBJECTIVE We have developed and validated a two-site immunoassay for t he measurement of dimeric inhibin in plasma and subsequently measured dimeric inhibin levels in plasma through the normal female menstrual c ycle. DESIGN Recombinant inhibin added to plasma samples was quantitat ively recovered in both follicular and luteal phase, and serial diluti ons of samples were tested for parallelism to similar dilutions of rec ombinant 32 kDa inhibin. Daily samples were assayed from four women th rough a menstrual cycle. PATIENTS (a) Four groups of six women who (i) were in the follicular phase of a normal menstrual cycle, (ii) were i n the luteal phase of a normal menstrual cycle, (iii) were post-menopa usal and (iV) who had received hMG to induce superovulation. (b) Four healthy female volunteers aged 25-33. RESULTS Post-menopausal women ha d less than 2 ng/l of inhibin whereas six women treated with hMG had d imeric inhibin concentrations up to 1125 ng/l. during the menstrual cy cle was similar to that observed with previous inhibin assays although the magnitude of change was considerably greater. CONCLUSION The huma n ovary, in particular the corpus luteum, secretes significant amounts of dimeric and therefore biologically active inhibin.During the early follicular phase, at the time of onset of menstruation, extremely low levels of dimeric inhibin were found (3.4 ng/l (Cl 2.2-5.0)) while in the late follicular phase, there was a marked increase in dimeric inh ibin concentration. The concentration of dimeric inhibin was maximal ( 65.6 ng/l (Cl 53.1-81.1)) in the mid-luteal phase. The overall pattern of dimeric inhibin concentration