Biology of Reproduction, Vol 12, 368-382, Copyright © 1975 by Society for the Study of Reproduction

The Ultrastructure of the Canine Testicular Interstitial Tissue

¹ Life Sciences Division, Stanford Research Institute, 333 Ravenswood Avenue, Menlo Park, California 94025, and Department of Anatomy, Temple University Medical School, Philadelphia, Pennsylvania

The seminiferous tubules of the dog testis are surrounded by a boundary tissue composed of a basal lamina and a layer of peritubular cells that is from one to six cells thick. Myoid cells, arranged in a layer only one cell thick, are the innermost cells of the boundary tissue. These cells are characterized by the presence of numerous microfilaments 5 nm in diameter, micropinocytotic vesicles, intracellular densities near the plasma membrane, and a basal lamina on both faces. In the interstitial tissue, clusters of Leydig cells are enveloped by a basal lamina, and the individual cells are separated by a varying intercellular space. Leydig cells are joined by gap junctions, septate-like junctions, and rudimentary desmosomes. Within their cytoplasm are many 5-nm wide microfilaments. The smooth endoplasmic reticulum is seen either as tubules or simple cisternae separated by microfilaments in the less developed Leydig cells and as extensive whorls of fenestrated smooth endoplasmic reticulum surrounding lipid droplets or mitochondria in the larger Leydig cells. Another cell type is present in the dog testis that has many of the cytological characteristics of the Leydig cell. This cell, however, is located within the boundary tissue of the seminiferous tubules between the myoid cell layer and the lymphatic endothelium. These Leydig-like cells may represent a stage in Leydig cell differentiation. The testicular lymphatics occur both as vessels and as sinusoids and often separate the boundary tissue from the interstitial tissue.