The present study demonstrates the expression of adrenomedullin (ADM) in the rat Sertoli cells and its effect on inhibin production. The regulation of ADM by FSH and its interaction with endothelin 1 (EDN1) in the rat Sertoli cells have also been established. Primary culture of Sertoli cells secreted 414 ± 27 pg immunoreactive ADM per 10⁶ cells in 24 h and expressed Adm mRNA. In addition, the Sertoli cell was shown to co-express mRNAs encoding for the calcitonin receptor-like receptor (CALCRL) and receptor activity-modifying proteins (RAMPs) 1–3. These may account for the specific binding of ADM to the Sertoli cells. Administration of ADM to Sertoli cells resulted in an enhancement of basal and FSH-stimulated inhibin B production. On the other hand, the production of ADM and the mRNA levels of Calcrl and Ramp2 in the Sertoli cells were suppressed by FSH. The results suggest that ADM, via its control in the secretion of inhibin B, may play a role in regulating spermatogenesis as well as the hypothalamus-pituitary-gonad feedback system. In addition, like in the Leydig cell, ADM and EDN1 were found to regulate the production of each other in opposite directions in the Sertoli cells, suggesting the presence of yet another local regulatory mechanism in the rat testis that may be important in modulating testicular functions regulated by gonadotropins.