Localization of Inhibin Alpha‐Subunit Immunoreactivity in the Rat Adrenal Cortex

Inhibin, a water soluble, non‐steroidal glycoprotein hormone that inhibits follicle‐stimulating hormone secretion, is produced by the gonads and several non‐gonadal tissues (placenta, pituitary and brain). This study describes the presence of inhibin α‐chain‐immunoreactive cells in the adrenal cortex of intact adult male rats and the effects of hypophysectomy and adrenocorticotropin treatment on the expression of inhibin in that gland. In intact rats, the majority of the immunoreactive cells were found scattered in the zona glomerulosa and reticularis. The zona fasciculata contained only a few cells immunopositive for the inhibin α‐chain. No immunoreactive cells were found in the medulla. Hypophysectomy resulted in a dramatic reduction in α‐subunit immunoreactivity with only scattered cells observed in the zona glomerulosa and reticularis (0 to 2 cells/section). No immunoreactive cells were found in the zona fasciculata or the medulla. Following supraphysiologic adrenocorticotropin administration to hypophysectomized animals, the number of inhibin α‐chain‐immunoreactive cells significantly increased in each zone of the adrenal cortex. The most prominent changes were seen in the zona reticularis. Interestingly, in the adrenocorticotropin‐treated animals scattered immunopositive cells were also present in the medulla. Our results suggest that inhibin‐related peptide(s) exist within the adrenal gland and that the expression of these peptides is regulated by adrenocorticotropin. Inhibin‐related peptide(s) may, therefore, play a paracrine and/or endocrine role in the adrenal function.