Regulation of Biologically Active Dimeric Inhibin A and B From Infancy to Adulthood in the Male

Abstract

Inhibins are glycoprotein members of the transforming growth factor-β family that have been implicated in the control of spermatogenesis by exerting a negative feedback on FSH secretion. In addition, locally produced inhibins may play a role in paracrine regulation of testicular function. Immunoassays were used to measure the two biologically active dimeric forms of inhibin (inhibin A and B) in serum, seminal plasma, and urine. To better define their actions, inhibins were measured in the male during infancy, sexual maturation, and senescence. Inhibin B but not A was measurable in the serum of male newborns, infants, children, and adults. In adult males, measurable levels of inhibin B were detected in the seminal plasma but not the urine. The circulating levels of inhibin B increased shortly after birth and peaked at 4–12 months of age (210 ± 31 pg/mL). The concentration measured in the serum then decreased to a low of 81 ± 12 pg/mL of inhibin B from 3–9 yr of age followed by a gradual increase beginning ...