Inhibin B in men with normal and disturbed spermatogenesis

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Abstract
Inhibin, a dimeric gonadal glycoprotein, inhibits the production and/or secretion of follicle stimulating hormone (FSH). The major species currently recognized are inhibin A (αβ A subunit) and inhibin B (αβ subunit). In men, inhibin B seems to be the physiologically important form of inhibin. Therefore we measured serum inhibin B using a new two-site immunoenzymatic assay in 14 men (mean ± SEM age, 34.5 ± 0.7 years) with sperm counts >20 × 106/ml, in 35 men (mean ± SEM age, 36.4 ± 1.3 years) with oligozoospermia (sperm count 6/ml) and in men with azoospermia (three orchidectomized men, three men with Klinefelter's syndrome, 10 men with Kallmann's syndrome). We compared inhibin B concentrations with serum FSH and sperm concentrations. In men with normal sperm concentrations (44.7 ± 6.4 × 106/ml), the concentration of inhibin was 223 ± 18 pg/ml and of FSH 5.0 ± 0.7 IU/1; in patients with low sperm concentrations (3.7 ± 0.8 × 106/ml), the concentration of inhibin B was 107 ± 12 pg/ml and of FSH 12.2 ± 1.5 IU/1. In all patients, except those with hypogonadotrophic hypogonadism, the relationship between inhibin B and FSH concentrations was inverse (r = −0.69, P < 0.0001). In all patients the sperm concentration was positively correlated with inhibin B concentrations (r = 0.70, P < 0.0001) and negatively correlated with FSH concentrations (r = −0.37, P < 0.01). We conclude that inhibin B may be a marker of exocrine testicular function and could offer improved diagnosis and treatment modalities for male infertility.

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