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Morphometric Analysis of Leydig Cells in the Normal Rat Testis

Hiroshi Mori and A. Kent Christensen
The Journal of Cell Biology
Vol. 84, No. 2 (Feb., 1980), pp. 340-354
Stable URL: http://www.jstor.org/stable/1608983
Page Count: 15
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Morphometric Analysis of Leydig Cells in the Normal Rat Testis
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Abstract

Leydig cells are thought to be the source of most, if not all, the testosterone produced by the testis. The goal of this study was to obtain quantitative information about rat Leydig cells and their organelles that might be correlated with pertinent physiological and biochemical data available either now or in the future. Morphometric analysis of Leydig cells in mature normal rats was carried out on tissue fixed by perfusion with buffered glutaraldehyde, and embedded in glycol methacrylate for light microscopy and in Epon for electron microscopy. In a whole testis, 82.4% of the volume was occupied by seminiferous tubules, 15.7% by the interstitial tissue, and 1.9% by the capsule. Leydig cells constituted 2.7% of testicular volume. Each cubic centimeter (∼1 g) of rat testis contained about 22 million Leydig cells. An average Leydig cell had a volume of 1,210 μ m3 and its plasma membrane had a surface area of 1,520 μ m2. The smooth endoplasmic reticulum (SER), the most prominent organelle in Leydig cells and a major site of steroidogenic enzymes, had a surface area of ∼10,500 μ m2/cell, which is 6.9 times that of the plasma membrane and is 60% of the total membrane area of the cell. The total surface area of Leydig SER per cubic centimeter of testis tissue is ∼2,300 cm2 or 0.23 m2. There were 3.0 mg of Leydig mitochondria in 1 g of testis tissue. The average Leydig cell contained ∼622 mitochondria, measuring on the average 0.35 μm in diameter and 2.40 μm in length. The mitochondrial inner membrane (including cristae), another important site of steroidogenic enzymes, had a surface area of 2,920 μ m2/cell, which is 1.9 times that of the plasma membrane. There were 644 cm2 of inner mitochondrial membrane/ cm3 of testis tissue. These morphometric results can be correlated with published data on the rate of testosterone secretion to show that an average Leydig cell secretes ∼0.44 pg of testosterone/d or 10,600 molecules of testosterone/s. The rate of testosterone production by each square centimeter of SER is 4.2 ng/d or 101 million molecules/s; the corresponding rate for each square centimeter of mitochondrial inner membrane is 15 ng testosterone/d or 362 million molecules/s.

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