Immunoassayable somatomedin C in seminal plasma of azoospermic men

Somatomedin C is a Sertoli cell peptide and since measurements of other Sertoli cell products in semen have provided a useful indices of testicular function, it was considered pertinent to measure the semen levels of Somatomedin C. Somatomedin C was measured by RIA in seminal plasma of vasectomized subjects (n = 18), subjects with agenesis of the seminal vesicles and vasa deferentia (n = 6) and subjects with azoospermia resulting from seminiferous tubule damage without obstruction (n = 23). Normal fertile subjects (24 men with a sperm concentration greater than 20 X 10(6)/ml) were used as controls. In all subjects, seminal levels of transferrin were also measured as an index of Sertoli cell function. The majority of seminal Somatomedin C appears to derive from the testis and/or epididymis. However, in several normal controls seminal levels of Somatomedin C (median = 3.52; range = 1.10-15.67 U/ejaculate) were found to be within the range for vasectomized subjects (median = 0.78; range = 0.46-4.20 U/ejaculate). In subjects with azoospermia the seminal levels of Somatomedin C (median = 2.06; range = 0.60-10.12 U/ejaculate) were significantly lower (P less than 0.02) than in fertile controls. However, values for these two groups overlapped. It is concluded that Somatomedin C in semen is not a reliable index of seminiferous tubule function and does not appear to be of diagnostic value in male infertility.