Gonadal and extragonadal expression of inhibin alpha, beta A, and beta B subunits in various tissues predicts diverse functions.

The S1-nuclease analysis was used to investigate the pattern of inhibin expression in the rat. In a first series of experiments, expression of the alpha, beta A, and beta B subunits of inhibin were monitored in various tissues from male and female rats. Two observations emerge from these studies. First, expression of inhibin subunits was found in gonadal and extragonadal tissues. In addition to the ovary and testis, inhibin alpha, beta A, and beta B RNAs were detected in the placenta, pituitary, adrenal, bone marrow, kidney, spinal cord, and brain. Detection of inhibin RNAs in the brain and spinal cord suggested that these subunits may exert neuroregulatory functions in the central and peripheral nervous systems. Furthermore, the presence of inhibin alpha and beta subunits in the placenta and the pituitary gland, two cell types that have clearly been shown to be regulated by exogenous inhibin, may reflect existing paracrine and/or autocrine processes active in these tissues. The second observation is that expression of inhibin subunit RNAs may vary by severalfold in a tissue-specific fashion. for example, alpha-subunit RNA levels are abundant in the gonads, whereas beta A-subunit RNA is predominant in the placenta and bone marrow. Finally, it is noted that expression of testicular inhibin RNA subunits decreases during sexual maturation. We conclude that the dimers comprised of inhibin subunits possess diverse functions and may act as growth/differentiation factors as well as a hormone.