Orthokeratinized epithelia of the rat showed regionally differing reproducible responses to a diet containing 1.7 ppm of zinc. Responses ranged from 100% conversion to parakeratinization in buccal mucosa and less complete conversion in other regions to total absence of experimental changes in palatal mucosa.
Susceptible regions showed persistence of pericellular glycoproteins, of cytoplasmic basophilia and nucleolar prominence in upper cellular layers, in addition to retention of nuclei in the keratin layer. Furthermore, thickening of keratin and cellular layers was followed by a progressively increased rate of cell division.
Alvares OF, Meyer J. Regional Differences in Parakeratotic Response to Mild Zinc Deficiency. Arch Dermatol. 1968;98(2):191-201. doi:10.1001/archderm.1968.01610140089022