The heterogeneity of Leydig cells from mouse and rat testes — evidence for a Leydig cell cycle?

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Abstract
A method for purifying Leydig cells by centrifugation of testes cells on continuous density gradients of Percoll has been investigated. The distribution of Leydig cells in the separated bands of cells obtained and their receptor content and testosterone production after addition of lutropin (LH) has been measured. In agreement with previous work (Schumacher, Schäfer, Holstein & Hilz 1978) it was found that highly pure mouse Leydig cells (average density 1.070 g/ml) could be prepared by this method. These cells responded to LH and produced high amounts of testosterone (1–4 μg/106 cells/2 h), and bound [125I]hCG specifically (25–64 fmols hCG bound/106 cells). Similarly from rat testes, Leydig cells (average density 1.072 g/ml) were purified. These cells also responded to LH and produced 5–25 ng testosterone/106 cells/2 h and bound [125I]hCG specifically (3–18 fmols hCG bound/106cells). Two other bands of nucleated cells of lower density (approximately 1.045 and 1.052 g/ml) were formed on the gradients from both mouse and rat testes. Both these bands of cells were found to contain Leydig cells which bound [125I]hCG specifically but little or no stimulation of testosterone production could be demonstrated. Fractionation of the gradients after separation of the cells into small aliquots demonstrated that fractions containing up to 100% Leydig cells could be isolated which were not stimulated to produce testosterone after addition of LH. It is concluded that in both the adult rat and mouse testes, Leydig cells of different densities and steroidogenic responsiveness to LH exist. The data obtained in this and other studies suggest that Leydig cells in the rat and mouse testes are not a homogeneous population and that they may be undergoing a continuous cycle of activity which involves changes in density and steroidogenic capacity.