Activity of intestinal carbohydrases responds to multiple dietary signals in nestling House sparrows

BRZEK, P.; KOHL, K.; CAVIEDES VIDAL, E.; KARASOV, W. H.

BOSTON, MASSACHUSETTS

Congreso; Society for Integrative Comparative and Biology; 2009

Society for Integrative Comparative and Biology

A simple adaptive modulation hypothesis predicts that digestive enzyme levels are matched to relative levels of dietary substrate so that energy does not escape the digestive tract unabsorbed and available membrane space and synthetic energy are not wasted on enzymes far in excess of need. But curiously, a predicted increase in intestinal maltase activity in individuals fed high carbohydrate diet has been observed in only two of seven studies on Passerine birds. We investigated whether differences in dietary lipid might account for the confusing results. We raised house sparrow (Passer domesticus) nestlings on a starch free diet A (0% starch, 20% corn oil, 60% protein), and two diets containing starch but with different oil contents: diet B (25% starch, 8% oil, 46% protein) and diet C (25% starch, 20% oil, 34% protein). On diets with similar lipid content (A and C), maltase and sucrase activities summed over entire small intestine were specifically almost doubled in birds fed diet with starch. But, on diets with similar starch content (B and C), summed carbohydrases activities were one third lower in birds fed more lipid. There was no significant effect of diet on summed activity of aminopeptidase-N. The changes in carbohydrase activities were thus consistent with the adaptive modulation hypothesis, but high oil had a counteracting effect on carbohydrase activities of nestlings. The emerging picture is that digestive enzyme levels respond in a complex manner to multiple dietary signals probably via multiple regulatory pathways. Supported by NSF IOS-0615678 to W.H.K.