title: Inhibin B in seminal plasma: testicular origin and relationship to spermatogenesis.
abstract: In men, inhibin B is the circulating isoform involved in the regulation of follicle stimulating hormone (FSH) secretion. Within the testis, inhibin B may have a role in Sertoli and germ cell interactions, thus secretion into seminal plasma may reflect seminiferous tubule function. Using specific immunoassays, inhibin B was present in seminal plasma in fertile men (n = 105) and in unselected men attending an infertility clinic (n = 174) with a wide range in concentration from undetectable (<15 pg/ml) up to 54,100 pg/ml (geometric mean 280 pg/ml). There was a highly significant correlation between seminal plasma inhibin B concentration and sperm concentration (r = 0.46, P < 0.001), but no correlation with percentages of spermatozoa with progressive motility or normal morphology. Inhibin A and isoforms containing pro and alphaC immunoreactivity were not detectable. In post-vasectomy seminal plasma samples (18 of 20) inhibin B was undetectable, indicating that the testis is the predominant source. In unselected men attending an infertility clinic, inhibin B was undetectable in 17% (present in remainder; maximum concentration 26,200 pg/ml; mean 263 pg/ml), with a highly significant correlation between seminal plasma inhibin B and sperm concentration (r = 0.55, P < 0.0001). In men with oligo/ azoospermia (sperm concentration <20 x 10(6)/ml), seminal plasma inhibin B concentrations were lower in those with elevated plasma FSH concentrations (mean values 42 and 205 pg/ml, P < 0.05). Inhibin alpha and betaB subunits were localized predominantly in Sertoli and Leydig cells, using immunohistochemistry. We conclude that inhibin B of testicular origin is present in normal human seminal plasma, but with a very wide range in concentration, and may reflect the functional state of the seminiferous epithelium.
authors.affiliation: Department of Obstetrics and Gynaecology, Centre for Reproductive Biology, University of Edinburgh, UK.
authors.forename: R A
authors.initials: RA
authors.lastname: Anderson
authors.forename: D S
authors.initials: DS
authors.lastname: Irvine
authors.forename: C
authors.initials: C
authors.lastname: Balfour
authors.forename: N P
authors.initials: NP
authors.lastname: Groome
authors.forename: S C
authors.initials: SC
authors.lastname: Riley
mesh_terms: D000328:Adult; D005298:Fertility / Q000502:physiology; D006801:Humans; D007150:Immunohistochemistry; D007248:Infertility, Male / Q000378:metabolism; D007265:Inhibins / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D009994:Osmolar Concentration; D011184:Postoperative Period; D012661:Semen / Q000378:metabolism*; D013091:Spermatogenesis / Q000502:physiology*; D013737:Testis / Q000378:metabolism*; D014659:Vasectomy
chemical_list: D007265:Inhibins