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Selective depletion of testicular macrophages and prevention of Leydig cell repopulation after treatment with ethylene dimethane sulfonate in rats.

Testicular macrophages were selectively eliminated with dichloromethylene diphosphonate-containing liposomes (Cl2MDP-lp) to study the role of these cells in the repopulation of Leydig cells after treatment with ethylene dimethane sulfonate (EDS). Right testes were injected with Cl2MDP-lp to deplete macrophages and left testes were injected with sodium chloride and served as controls. Injection of Cl2MDP-lp produced a 97% reduction in the number of macrophages 10 days after treatment. Twenty-one days after destruction of the existing Leydig cells with EDS, abundant differentiating Leydig cells were present in the left (macrophage-containing) testes. On the contrary, in the right (macrophage-depleted) testes, differentiating Leydig cells were scarce, and was 3% of that found in the control testes. The inhibition of Leydig cell repopulation in macrophage-depleted testes was more evident at 30 days after EDS treatment, when the number of Leydig cells in the right testes was 1% of that found in control testes. The lack of Leydig cell development was also indirectly shown by the lower mass and more atrophic seminiferous epithelium of the right testes, as well as the decreased weight of the ipsilateral epididymis compared with the left testes. These results indicate that testicular macrophages are central to the proliferation and differentiation of new Leydig cells after EDS treatment, and point out the significance of paracrine regulatory mechanisms in rat testes.