Abstract
A study was conducted to investigate the effects of hydrocortisone and vitamin D3 on the fatty acid composition of the duodenal brush border membranes in developing chick embryos, and to observe whether such effects on membrane lipids are related to the developmental induction of membranebound enzyme activity. Hydrocortisone was administered to embryos on days 14 and 17 of incubation, and vitamin D3 was administered on day 14 of incubation. The duodenal brush border membranes were isolated from the pooled duodenal mucosa of 10 or 15 embryos on day 20 of incubation. The administration of hydrocortisone resulted in an increase of duodenal mucosa weight and DNA content of the duodenal mucosa in 20-day-old embryos. The embryonic membrane protein in the duodenal brush border was also increased through this treatment. However, there was no increase of membrane protein as expressed per unit of mucosal DNA. Administration of vitamin D3 had no effects on these parameters. The fatty acid composition of the duodenal brush border membranes was changed by both hydrocortisone and vitamin D3 administration. The polyunsaturated fatty acid levels of ω6 acids such as 18: 2 (ω6) and 20: 4 (ω6) were significantly increased by both treatments. Hydrocortisone administration enhanced the specific activities of sucrase and alkaline phosphatase in the duodenal brush border membrane af 20-day-old chick embryos. However, vitamin D3 treatment increased alkaline phosphatase activity anly. Induction of alkaline phosphatase related to a change in fatty acid composition was thus caused by treatment with either hydrocortisone or vitamin D3. Sucrase induction was not related to alteration of membrane lipids. These results suggest that hydrocortisone as well as vitamin D3 might be involved in the developmental induction of membrane-bound enzyme (alkaline phosphatase) activity, affecting membrane fluidity through alteration of the membrane fatty acid composition.
