Human dermal microvasculature: II. Enzyme histochemical and cytochemical study

An enzyme histochemical and cytochemical study of normal dermal microvasculature showed that respiratory enzymes, lipase and non-specific esterase occurred in all vascular segments. Lysosomal enzymes were also widely distributed and acid phosphatase activity was localized in lysosomes, Golgi apparatus and small portions of endoplasmic reticulum of both endothelial cells and pericytes. Alkaline phosphatase activity, however, was confined to the arterial side and tip of the capillary loop where it occurred in vesicles along the luminal surface of the endothelium and in junctions between endothelial cells. The localization of nucleoside phosphatase activity within the endothelium varied according to substrate; with adenosine triphosphate as substrate, the reaction product occurred in vesicles distributed throughout the endothelial cells; with adenosine diphosphate it was limited to vesicles along the luminal surface; and with adenosine monophosphate, activity was mostly localized to the lateral surfaces of endothelial cells. These findings suggest functional variation between different vascular segments and between various components of the endothelium. Attempts to demonstrate a specific Na+K+ adenosine triphosphatase (transport ATPase) within the endothelium were not successful.