Zinc deficiency produces time-related ultrastructural changes in rat cheek epithelium

The subject of this study was whether the ultrastructural changes in cheek epithelium of zinc-deficient rats are time related. Weanling male Sprague Dawley rats were fed a zinc-deficient diet containing 0.4 ppm zinc (ZD) ad libitum and controls were pair-fed zinc adequate diet containing 40 ppm zinc. After 9, 18, and 27 days of zinc deficiency, specimens from cheek epithelium of both groups were processed for transmission electron microscopy. Partial conversion of the orthokeratinized cheek epithelium to parakeratinized was seen as early 9 days. An electron-lucent band surrounding the nucleus was observed in ZD cells. Mitochondria, tonofilaments, keratohyalin granules and ribosomes seemed to be increased with the increase in time of zinc deficiency. There was a thickening of the stratum corneum as well as hyperplasia and widening of the intercellular spaces of the spinous layer cells. Retention of a few membrane coating granules (MCGs) in the parakeratinized layer was seen after 9 days. Parakeratinization was further increased after 18 days of zinc deficiency, and the number of MCG profiles also increased. The epithelium was fully parakeratinized following 27 days of zinc deficiency, and the number of MCG profiles was increased. It was concluded that zinc deficiency affected cell proliferation and differentiation of the epithelium as early as 9 days, and caused a delay in loss of nuclei and MCGs in parakeratinized cells.