Intestinal alkaline phosphatase secretion in oil-fed rats

Oil feeding is known to increase the secretion of intestinal alkaline phosphatase (IAP) into serum and this phenomenon is shown to be mediated by surfactant-like particles. These lipoprotein particles are secreted by enterocytes and are rich in phosphatidyl choline and IAP. The exact mechanisms underlying this phenomenon are not known. We studied the effect of feeding different oils varying in fatty acid composition, i.e., coconut oil, corn oil, and cod liver oil, on the secretion of IAP into serum. Also, the effect of actinomycin D treatment on this phenomenon was evaluated. Male albino rats were fed 2 ml of various oils. Alkaline phosphatase activity was measured in serum, luminal washings, and other intestinal fractions. Cod liver oil was found to maximally enhance the soluble and membrane-bound IAP as well as secretion of IAP into lumen and serum. Administration of actinomycin D significantly reduced the enzyme activity in serum and various intestinal fractions in both control and cod liver oil-fed rats. These results were further substantiated by 5-bromo-4-chloroindolyl phosphate staining of IAP in acrylamide gels and by western blotting. The effect of cod liver oil feeding was specific for IAP, as there was no change in the activity of another brush border enzyme, sucrase, under these conditions. These findings suggest that fatty acid composition of the oil determines the amount of IAP secretion and there is coordination between IAP synthesis and its secretion for transport into serum in response to oil feeding.