EFFECTS OF SPECIFIC DIETARY SUGARS ON THE INCORPORATION OF C-13 LABELFROM DIETARY GLUCOSE INTO NEUTRAL SUGARS OF RAT INTESTINE AND SERUM GLYCOPROTEINS

Although theoretically all glycoprotein sugars can be derived from glu cose, it may be hypothesized that specific dietary sugars could be pre ferential substrates for glycoprotein synthesis. To test this hypothes is, groups of rats received either continuously (continuous-labelling experiment) or for a single nutritional period (pulse-labelling experi ment) a C-13-rich diet containing either maize starch or artificially labelled [C-13]glucose. Some groups of rats were also provided during a single nutritional period with low amounts (20-200 mg/animal) of low -C-13 dietary sugars (mannose, galactose, fucose or fructose). If spec ific dietary sugars were preferentially incorporated into glycoprotein s instead of glucose-derived labelled sugars, a decrease would be expe cted in the intestinal or serum glycoprotein-sugar C-13 enrichment mon itored by gas chromatography-isotope-ratio mass spectrometry (GC-IRMS) . Contrary to this hypothesis the results showed no significant decrea se with any of the specific dietary sugars. Furthermore, with dietary low-C-13 mannose or galactose, a significant increase in C-13 enrichme nt of glycoprotein-sugars was observed compared with some other nutrit ional groups. Moreover, in the pulse-labelling experiment, dietary man nose and galactose induced similar patterns of C-13 enrichment in inte stinal and serum glycoprotein-sugars. Therefore, although specific die tary sugars do not appear to be preferential substrates for glycosylat ion under conditions and doses relevant to current concepts of nutriti on, regulatory roles of some specific dietary sugars in relation to gl ycoprotein-sugar metabolism might be hypothesized. These findings coul d lead to similar studies using stable-isotope methodology in man whic h could have practical consequences, especially in parenteral nutritio n where glucose is the only sugar provided to the metabolism.