It has been established that these reductions are specifically due to the loss of functional Leydig cells rather than changes in circulating gonadotropin levels. Leydig cells have direct contact with testicular macrophages through intimate structural specializations. Leydig cells also produce locally high levels of androgens, and there is evidence that sex steroids including androgens have the potential to regulate some monocyte and macrophage functions (reviewed in ). Recent studies indicate that macrophage-migration inhibitory factor (MIF), a cytokine secreted by lymphocytes and macrophages during inflammation that stimulates monocyte infiltration and proliferation, is constitutively produced by adult rat Leydig cells under normal noninflammatory conditions. Finally, Leydig cells regulate the normal spermatogenic function of the seminiferous tubules by producing adequate levels of testosterone, and the seminiferous tubules produce several cytokines with known effects on macrophage function, such as interleukin-1a and transforming growth factor p. Consequently, the Leydig cells may regulate testicular macrophage numbers in the adult testis either directly, or indirectly via control of seminiferous tubule secretions. buy prednisone
In the study reported here, the potential roles of the seminiferous tubules and the specific Leydig cell products, testosterone and MIF, in regulating macrophage numbers in the adult rat testis were investigated. This was done by examining the response of the testicular macrophage subsets to manipulation of seminiferous tubule and Leydig cell function by the combined use of surgical cryptorchidism and s.c. testosterone implants.