Disruption of endoplasmic reticulum is the primary ultrastructural lesion of the pancreas in the selenium-deficient chick.

Severe uncomplicated selenium (Se) deficiency was produced in chicks by feeding, from 1 day of age, a purified diet that contained 0.010 ppm Se but was adequate with respect to all other known nutrients. The deficiency was characterized by depressions in rate of growth and efficiency of feed utilization and by reductions in the plasma activity of Se-dependent glutathione peroxidase (SeGSHpx) by 85-97% from levels in chicks fed the basal diet supplemented with 0.20 ppm Se as Na2SeO3. Histological observations of the target organ of Se deficiency in the chick, i.e., the pancreas, using transmission electron microscopy, showed severe losses of endoplasmic reticulum (ER) and absence of secretory granules in acinar cells of Se-deficient animals. These effects were not uniform within individuals, as Se-deficient pancreases also showed areas of unaffected acini. By 14 days of age, Se-deficient pancreases contained many apparently undifferentiated cells, which were absent from pancreases of Se-fed chicks. It is noteworthy that abnormal mitochondria were not observed in any pancreas sections. It is concluded that the metabolic consequences of severe uncomplicated Se deficiency in the chick result from the disruption of ER and loss of functional acinar cells, rather than to damage to mitochondria as previously suggested.