Inhibin B in seminal plasma: testicular origin and relationship to spermatogenesis.

Human Reproduction Inhibin B in seminal plasma: testicular origin and relationship to spermatogenesis Richard A.Anderson 2 3 D.Stewart Irvine 1 Claire Balfour 2 Nigel P.Groome 0 Simon C.Riley 2 0 School of Biological and Molecular Sciences, Oxford Brookes University , Oxford , UK 1 MRC Reproductive Biology Unit, Centre for Reproductive Biology, University of Edinburgh , Edinburgh 2 Department of Obstetrics and Gynaecology, Centre for Reproductive Biology, University of Edinburgh , 37 Chalmers Street, Edinburgh 3 Current address: Department of Reproductive Medicine, University of California San Diego , USA 5To whom correspondence should be addressed - 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 5 105) and in unselected men attending an infertility clinic (n 5 174) 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 5 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 aC 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 5 0.55, P , 0.0001). In men with oligo/ azoospermia (sperm concentration ,203106/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 a and bB 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. Key words: inhibin/Sertoli cell/spermatogenesis/testis The inhibin/activin family of dimeric peptide hormones are produced in the testis and are postulated to have paracrine and autocrine roles in the regulation of steroidogenesis and spermatogenesis (Lin et al., 1989; Chen, 1993; Mather et al., 1997) in addition to endocrine regulatory effects on follicle stimulating hormone (FSH) secretion (Burger and Igarashi, 1988). Inhibins are composed of a dimer of a common subunit and either a A (inhibin A) or B (inhibin B) subunit, while the activins are subunit dimers resulting in activin A (AA), activin B (BB) and activin AB (AB). The development of immunoassays specific for the dimeric forms has allowed the demonstration that inhibin B but not inhibin A is present in male serum in both fetus and adult (Anawalt et al., 1996; Illingworth et al., 1996; Wallace et al., 1997). The various inhibin/activin subunits have been localized in testis as messenger RNA and proteins. In the adult rat, the , A and B subunits were present in both Sertoli and Leydig cells (Roberts et al. 1989; Klaij et al. 1994) and in adult monkey, mRNA for all three subunits was localized predominantly in Sertoli cells (Zhang et al., 1997). The expression of mRNA in Sertoli cells varies with the stage of the seminiferous cycle (Bhasin et al. 1989), with differences between the various subunits possibly reflecting differential production of activin and inhibin (Klaij et al. 1994). In the human, subunit immunostaining is present in both Leydig and Sertoli cells (Bergh and Cajander, 1990), with an increase in positive staining in Leydig cells after human chorionic gonadotrophin (HCG) treatment and increased staining in Sertoli cells in conditions of impaired spermatogenesis. The A subunit has also been localized to both Leydig and Sertoli cells in normal adult testis, although the antibody used cross-reacted with the B subunit (Vleigen et al. 1993). In the fetal human testis, and B but not A subunits were immunolocalized in Leydig and Sertoli cells (Majdic et al. 1997), whereas A mRNA was predominantly found in the interstitial cells, and B mRNA was predominantly localized in the seminiferous tubules (Roberts, 1997). The distribution of the B subunit in adult human testis has not been described. Inhibin bioactivity is present in human seminal plasma (Scott and Burger, 1980, 1981; Robertson et al. 1989), and shows a positive relationship with sperm concentration and an inverse relationship with FSH concentration (Scott and Burger, 1981). However, bioactive inhibin concentrations in seminal plasma were normal following vasectomy. Cultured primate Sertoli cells secrete bioactive inhibin in a highly vectorial manner, the majority of secretion being into the adluminal compartment (Handelsman et al., 1990) and inhibin secretion European Society for Human Reproduction and Embryology in vitro is increased in response to FSH and in the presence of germ cells (Handelsman et al., 1990; Carreau, 1995). While inhibin B secretion into blood has been demonstrated to be of physiological relevance and to be under gonadotrophin, and particularly FSH, control (Anawalt et al. 1996; Illingworth et al. 1996; Nachtigall et al. 1996; Anderson et al. 1997), secretion into seminal plasma, which may more closely reflect the functional state of the seminiferous epithelium, has not been investigated. Here we report the presence of inhibin forms in seminal plasma and the relationship between inhibin B concentrations and spermatogenesis in men recruited from three groups: (i) men who had recently fathered pregnancies, (ii) men who had had a vasectomy and (iii) men attending an infertility clinic, with a wide range of reproductive function from normal to severely abnormal. Materials and methods Group 1. Fertile men This group comprised 105 men (mean age 33 years, range 2245) who were part of an ongoing programme to recruit semen donors for research purposes from antenatal parentcraft classes in a local maternity hospital and had fathered ongoing pregnancies 2037 weeks previously. Clinical history and physical examination were normal in all cases and semen quality was assessed according to WHO criteria (World Health Organization, 1992). Peripheral blood samples were obtained simultaneously, the plasma separated and stored at 20C until assay. Group 2. Post-vasectomy men This group comprised 20 men (mean age 35 years, range 2645) submitting routine semen samples 12 weeks after bilateral vasectomy. Group 3. I (...truncated)