The fine structure of the interstitial tissue of the rat prostate

The structure of the interstitial tissue of the rat prostate has been studied using the light and electron microscopes in an attempt to determine the role of the fibromuscular stroma in the normal functioning of the gland. Smooth muscle cells and fibroblasts are the most numerous cell types. They are accompanied by macrophages, mast cells, and undifferentiated cells of low electron density. Smooth muscle cells have cytoplasmic protrusions that extend into corresponding depressions in adjacent muscle cells, and, at these points, the intercellular space is narrowed to 150–2000 Å. Smooth muscle cells and fibroblasts are arranged in parallel in septa between adjacent epithelial alveoli and form a sheath around each alveolus. Proceeding peripherally from the epithelium into the interstitial tissue, this sheath is composed of a layer of one or two highly flattened fibroblasts and a parallel layer of smooth muscle cells, followed subsequently by additional layers of fibroblasts and smooth muscle that merge into the remainder of the interstitial tissue. Most of the capillaries have an uninterrupted endothelium, but in some regions endothelial fenestrations are present. Unmyelinated axons contain aggregations of small granular and agranular vesicles. Vesicles are found in axons at distances up to several thousand angstroms from muscle cells and in axons that approach to within 150–200 Å of smooth muscle cells. In some cases an axon lies in a deep depression in the surface of a muscle cell. The type of innervation and variety of intercellular contact between muscle cells is discussed in relation to probable physiological characteristics of the tissue.