Histopathological and histochemical studies of the skin of guinea pigsafter long-term exposure to nitrogen dioxide

Summary Male guinea pigs were exposed to nitrogen dioxide (2 mg/m 3 ) during 180 days (8 hours a day). Long-term exposure induced thickening of the corneal layer of the epidermis as well as inflammatoryinfiltrations in the proper skin. The following enzymes were estimated histochemically in skin samples of experimental and controlanimals: succinic dehydrogenase, NADH 2 -tetrazolium reductase, lactate dehydrogenase; alkaline phosphatase, acid phosphatase and adenosine triphosphatase. Chronic exposure stimulated a decrease of NADH 2 -tetrazolium reductase in the epidermis andconnective tissue components of proper skin and marked positive reaction of lactate dehydrogenase in epidermal cells and hair follicles. Increase of a diffuse reaction on adenosine triphosphatase in smooth muscles of the skin was found also in exposed animals.