Skin response to X-irradiation in the guinea-pig

Ultrastructural evaluation of the radioprotective effects of melatonin against X-ray-induced skin damage in Albino rats

Our knowledge about the radioprotective effects of melatonin against X-ray-induced skin damage is still lacking. To examine these effects, an animal model of 60 Albino rats was used. The animals were divided into five groups: Group 1, nonirradiated; Group 2, X-ray irradiated (XRI, 8 Gy); Group 3, XRI pretreated with solvent (ethanol and phosphate-buffered saline); Group 4, nonirradiated group treated with melatonin; and Group 5, XRI pretreated with melatonin. The skin was evaluated for ultrastructural changes using transmission electron microscopy (TEM). When compared to the nonirradiated skin (Groups 1 and 4), XRI skin (Groups 2 and 3) showed features of both cell injury and increased metabolic activity. The former included changes such as condensation of the nuclei, vacuolization of the cytoplasm, dilatation of the rough endoplasmic reticulum, swelling of the mitochondria with cristolysis, destruction of the ribosomes and intermediate filaments, fragmentation of the keratohyaline granules and loss of the irregularity of the basal cell borders. The central cells of the sebaceous gland alveoli had larger irregular nuclei and few lipid droplets in their cytoplasm. The hair follicle cells had heterochromatic nuclei and less electron dense cytoplasm containing few complements of the organelles. The features of increased metabolic activity included increased euchromatin, irregularity of the nuclear membrane and increased branching of the melanocytes. Also, an increased number of the Birbeck granules were seen in the Langerhans cells. When compared to the irradiated skin (Groups 2 and 3), these changes were mild or absent in the skin of XRI animals pretreated with melatonin (Group 5). The ability of melatonin to minimize the injurious effects of XRI suggests a radioprotective role. The clinical ramifications of these observations warrant further studies.

Split-dose recovery in epithelial and vascular-connective tissue of pig skin

In the first 16 weeks after irradiation, two distinct waves of reaction can be observed in pig skin; the first wave (3-9 weeks) represents the expression of damage to the epithelium while the second is indicative of primary damage to the dermis, mediated through vascular injury. Following beta-irradiation with a strontium-90 applicator, a severe epithelial reaction was seen with little subsequent dermal effects. X-rays (250 kV) on the other hand, produced a minimal epithelial response at doses which led to the development of dermal necrosis after 10-16 weeks. Comparison of single doses with two equal doses separated by 24 h produced a D2-D1 value of 7.0 Gy at the doses which produced moist desquamation in 50% of fields (ED50) after strontium-90 irradiation. After X-irradiation comparison of ED50 doses for the later dermal reaction suggested a D2-D1 value of 4.5 Gy. Over this same dose range of X-rays the D2-D1 value for the first wave epithelial reaction was 3.5 Gy. These values of D2-D1 for epithelial and dermal reactions in pig skin were compared with published data and were examined in relation to the theoretical predictions of a linear quadratic model for tissue target cell survival. The results were broadly in keeping with the predictions of such a model.

Leg contracture in mice: an assay of normal tissue response

Leg contracture, defined as the difference in extensibility of the control and irradiated hind legs of mice, was found to correlate with single doses of radiation from about 20 to 80 Gy. The time of development of the early phase of the response coincided with that reported for the appearance of the acute skin response, and in some cases, partially reversed as this reaction healed. The contracture then progressed again at a moderate rate through 90 days, and then more slowly through one year. Skin contraction, measured by decrease in intertattoo distance, was assayed in the same mice. It followed the same time course as leg contracture, but had a different dose-response relationship. Maximal contraction occurred following doses of 30 Gy or more, reaching this level sooner following higher doses. The early reactions in individual mice were not reliable in predicting late response for either assay. To determine the contribution of skin contraction to the overall leg contracture response, mice were sacrificed and the leg contracture measured before and after the removal of the skin of the leg. After doses of up to 30 Gy, little contracture remained from skinning the leg, indicating that skin contraction was largely responsible for leg contracture in this dose range. After doses of about 45 Gy and above, some contracture remained in the skinned legs, although less than in intact legs. This indicated that injury to the deeper tissues of the leg as well as to the skin was responsible for contracture at these higher doses. There was little or no enhancement of either skin contraction or leg contracture by the hypoxic cell sensitizers metronidazole or misonidazole.

Persistent and late occurring lesions in irradiated feet of rats: their clinical relevance

Radiation-induced deformity, as characterized by tissue loss, has been investigated in rat feet. The acute epithelial response and the loss of deeper tissues occur concomitantly after irradiation. The greatest loss of tissue (severe deformity) was produced in feet where the healing of the epithelial reaction was greatly delayed. While deformity will clearly continue to "persist" after the acute reaction has healed it is misleading to refer to this lesion as "late" damage. A late-occurring lesion, not previously described in the literature, can be produced in the rat foot by high doses of radiation delivered in such a way that moist desquamation is avoided, i.e. by extending the total treatment time. The "persistent" and "late" radiation lesions are discussed in relation to other published data on the radiation response of rodent skin in the foot, ear and tail. Parallels are also drawn between reactions in rodents and those in the skin of pig and man.