harmful effect of chronic hypervitaminosis D[3] on the skin and cardiac muscle of albino rat. A histological study

ABSTRACT

Is to investigate the effect of hypervitaminosis D[3] on the skin and cardiac muscle of albino rats. Eighteen adult male albino rats were used in this study. Rats were divided into two main groups. Group I [6 rats] served as a control group. Group II. [12 rats] to which vitamin D[3] were administered in a daily dose of 50,000 IU/kg body weight and subdivided into two subgroups. [Subgroup IIa] 6 rats received the preparation for two weeks and [Subgroup IIb] 6 rats received the preparation for eight weeks. At the end of experimental periods, specimens were taken from the skin covering the back and the left ventricles of the heart of each animal. Animals of subgroup IIa showed epidermal affection as focal areas of decreased number of epidermal layers except for thickened stratum corneum, widening of the intercellular spaces between keratinocytes, loosened desmosomal junctions and microvillous transformation of the plasma membrane. These changes were marked and diffuse in animals of subgroup IIb. Layers beneath the stratum corneum were only one or two layers. Keratinocytes showed affection of the nuclei. The cytoplasm showed increased cytokeratin filaments and keratohyaline granules. Stratum corneum appeared thickened with wide spaces in between its layers and failure to form intact wavy bundles. Increased deposition of collagen bundles were noticeable in the dermis of most animals of this subgroup. The cardiac muscle of subgroup IIa showed damage of muscle fibers with widening of the spaces in between and interstitial odema, Breaking of continuity of myofibrils at the site of I band, partial degradation of Z-line material in many sarcomeres, thinning of myofibrils and mitochondrial swelling. The sarcolemma appeared lifted away from the underlying sarcomeres. Rats of subgroup IIb presented aggravation of these changes with severe cardiac muscle damage. Some cardiac myocytes appeared thinned with dark shrunken nuclei, others revealed dissolution with either karyolytic or pyknotic nuclei. Dehiscence of the intercalated disc with widened disc space, contraction bands with subsequent shrinkage of the sarcomere were also observed. Many myofibrils were disorganized, distorted and fragmented. The use of excessive doses of vitamin D resulted in severe damage to the skin and cardiac muscle. The use of vitamins should be restricted for individuals with documented deficiency or those at risk, especially fat-soluble vitamins because of their cummulative effect in the body