STUDIES OF THE ROLE OF SELENIUM IN MAINTAINING THE INTEGRITY OF THE EXOCRINE PANCREAS OF THE CHICK

Studies have been conducted to determine the role of selenium (Se) in maintaining the integrity of the chick exocrine pancreas. The activity of selenium-dependent glutathione peroxidase (Se-GSHpx) was found to decline in response to nutritional Se depletion at approximately the same time as the appearance of the histopathological changes in pancreatic acinar cells indicative of the onset of nutritional pancreatic atrophy (NPA). The activity of Se-GSHpx was significantly depressed in plasma by 5 days of Se depletion, and in pancreas and liver by 10 days at which time the first signs of NPA were noted by histological examination.

Mitochondrial respiratory function in the pancreas was not impaired directly by severe Se deficiency. No significant differences due to Se deficiency were found in the rates of oxygen uptake, ADP:oxygen ratios or respiratory control indices of isolated mitochondria; however, the yield of mitochondrial protein was decreased by 24-55% due to Se deficiency. Electron microscopical observations revealed severe disruption of acinar cell mitochondrial membranes. These data suggest that Se deficiency leads to a reduction in the amount of mitochondria in the pancreas.

Evidence was obtained that peroxidative damage to membrane lipids occurs in the pancreas of the Se-deficient chick. The relative amounts of several polyunsaturated fatty acids (i.e., 18:2, 20:3 n-6, 20:3 n-9, 20:4 n-6, 22:4 n-6, 22:5 n-3) in pancreatic mitochondria were significantly reduced by dietary Se deficiency. This effect was overcome by supplementing the Se-deficient diet with 500 ppm each of vitamin E, ascorbic acid or diphenyl-p-phenylene-diamine (DPPD). Antioxidant supplementation (i.e., DPPD, ascorbic acid, vitamin E, ethoxyquin, BHT) was found to prevent both NPA and the growth depression associated with a severe Se deficiency. Addition of 10% linoleic acid to the Se-deficient diet caused a severe growth depression and accelerated the development of NPA.

These findings provide indirect evidence that the role of Se in protecting the chick pancreas is as a component of the enzyme Se-GSHpx. The ability of vitamin E, ascorbic acid and synthetic antioxidants to relieve the symptoms associated with NPA has been taken as evidence for the functioning of Se in this fashion.