SECRETION PATTERN OF IMMUNOREACTIVE INHIBIN IN MEN

Chronological changes in serum concentrations of inhibin, a gonadal gl ycoprotein hormone, were studied in healthy male Volunteers (age 24-27 years). Secretion profiles of immunoreactive inhibin (ir-inhibin) wer e compared with those of luteinizing hormone (LH), follicle-stimulatin g hormone (FSK) and testosterone. Blood samples were collected every 1 5 min for 24 h. Serum inhibin concentrations were measured by a two-si te immunoenzymatic assay with antibodies raised against distinct epito pes of the recombinant 1-32 amino acids of the cr-subunit of human inh ibin, The normal range for men was 0.79-3.1 U/l x 10(-3), the sensitiv ity of the assay was 0.1 U/l x 10(-3) (cv: within-assay, 6.8%; between -assay, 8.2%). Luteinizing hormone and FSH were measured by immunoradi ometric assay and testosterone by radioimmunoassay. Secretion profiles of inhibin and testosterone were tested for diurnal Variations by cos inor rhythmometry. Highest ir-inhibin concentrations were observed in the morning at 08.00 h, with peak values of 2.45-3.20 U/l x 10(-3). Du ring the evening and the night, ir-inhibin levels were relatively low; lowest concentrations were observed between 01.00 h and 02.00 h at ni ght: 1.20-1.86 U/l x 10(-3). Highest testosterone levels were observed in the morning (20.5-36.6 pmol/l), lowest concentrations were detecte d at night (7.35-12.6 pmol/l). Cosinor rhythmometry supported the sugg estion that there is a clear circadian secretion of ir-inhibin and tes tosterone, respectively. The secretion pattern of ir-inhibin was analy zed by the Cluster pulse analysis computed algorithm, which identified four to seven inhibin pulses per day, depending on the person under o bservation, A significant correlation could be observed between median testosterone and ir-inhibin concentrations (r = 0.449, p < 0.001). In conclusion, ir-inhibin and testosterone in healthy male volunteers fo llow a clear diurnal rhythm. Moment to moment changes of ir-inhibin ca n be observed in al secretion profiles investigated. A probable physio logical role for pulsatile inhibin secretion is not yet clarified.