Stereological principles provide efficient and reliable tools for the determination of quantitative parameters of tissue structure on sections. Some principles which allow the estimation of volumetric ratios, surface areas, surface-to-volume ratios, thicknesses of tissue or cell sheets, and the number of structures are reviewed and presented in general form; means for their practical application in electron microscopy are outlined. The systematic and statistical errors involved in such measurements are discussed.

Rats were exposed to 98.5% oxygen at 765 torr for 6-72 hr. The pulmonary changes were investigatcd by electron microscopy and by morphomctric methods. A progressive thickcning of thc air-blood barrier, from the normal 1.5 to 3 # after 3 days, was duc primarily to enlargement of thc interstitial space by accumulation of edema which was replaced secondarily by cells and fibrin. This was accompanicd by destruction of about 50% of the capillaries. Morphomctric data allowed an cstimatc of the degree of impairment of lung function. The primary cellular damagc was located in endothelial cells which underwent cytoplasmic changes and, finally, fragmentation. In contrast, thc damage to the epithelial lining of alvcoli was relatively scarce compared to thc extcnsivc cndothclial changes. This pertained cven to severely damaged lungs with 65 % of the alveoli obliterated by a heterogeneous cxudatc. Possiblc causes for this apparently different reaction of epithelium (thc first target ccll) and cndothelium to toxic oxygen cffccts are discussed.

Background: In a previous study, we reported a significant and dose-dependent suppression of UV-induced erythema in human skin by a topically applied melatonin preparation. Objective: The present double-blind randomized study was designed to examine the influence of the application time point of topical melatonin on this antierythema effect. Methods: Defined small areas on the lower back of 20 volunteers were treated with 0.6 mg/cm² melatonin dissolved in a nanocolloid gel carrier either 15 min before or 1 30 or 240 min after UV irradiation with twice the individual minimal erythema dose delivered by a Multiport Solar UV Simulator (UVA and UVB). The erythemata induced were evaluated by visual scoring and chromametry 24 h after irradiation. Results: Treatment of the skin with melatonin 15 min before UV irradiation proved to almost completely suppress the development of an UV-induced erythema. In contrast, no significant protective effects of melatonin were observed when it was applied after UV irradiation. Conclusion: Topically applied melatonin has a clear-cut protective effect against UV-induced erythema. Free radical scavenging of UV-generated hydroxyl radicals and interference with the arachidonic acid metabolism are possible mechanisms of the melatonin action.

Oxygen-centred free radicals play an important role in the pathogenesis of acute and chronic UV-induced skin damage as well as in skin aging. In this double-blind randomized study the efficacy of topically applied melatonin (N-acetyl-5-methoxytryptamine), a potent free radical scavenger, in the suppression of UV-induced erythema was assessed. A group of 20 healthy volunteers were irradiated with 0.099 J/cm2 UVB on four 5-cm2 areas on the lower back and topically treated with various concentrations of melatonin (0.05, 0.1, 0.5%) in a nanocolloid gel as carrier or with carrier alone. The UV-induced erythema was examined 8 and 24 h after irradiation by visual scoring and chromametry. A distinct dose response relationship was observed between the topical dose of melatonin and the degree of UV-induced erythema. Significant differences (P < 0.05) were found in redness (chromameter a-value and visual scoring) 8 h after irradiation between the areas treated with melatonin at 0.5% and those treated with melatonin at 0.05% or with the carrier. These results might open a new approach in the prevention and control of free radical-influenced skin diseases.