Morphometric analysis of testicular Leydig cells in normal adult mice.

Stereological analysis was carried out on Leydig cells in perfusion-fixed testes of normal adult mice. In a decapsulated testis, the seminiferous tubules occupy 89.3% and the interstitial tissue makes up 10.7% of the volume of the testis parenchyma. The Leydig cells comprise 3.8% of testicular volume. There are 24.9 million Leydig cells per cm3 (or gm) of tissue. An average Leydig cell has a volume of 1,533 microns 3 and a surface area of 1150 microns 2. The smooth endoplasmic reticulum (SER) is the most prominent organelle in the Leydig cells, and has a membrane surface area of 2,428 cm2 per cm3 of fresh testis tissue, which is 8.5 times the surface area of the plasma membrane and constitutes 56.9% of the total membranes in Leydig cells. Mitochondria occupy 10.1% of the Leydig cell volume or 11.4% of cytoplasmic volume. The inner mitochondrial membrane (including tubular or vesicular cristae) provides a surface area of about 2855 microns 2/cell and is 2.26 times that of the outer membrane. There are approximately 712 cm2 of inner membranes per cm3 tissue. Mouse Leydig cells have numerous lipid droplets, which average 147 per cell and occupy 5.1% of the cell volume.