CHEDIACK, J.G.; CAVIEDES-VIDAL, E.; KARASOV, W.H.: Intestinal passive absorption of hydrosoluble compounds is size dependent and modulated by luminal nutrients in house sparrows (Passer domesticus).

We are characterizing the apparent paracellular permeability of the small intestine in intact birds. We previously found that L-glucose was substantial and enhanced by the presence of sugar in the lumen. In this study we extend the scope of our previous findings using other non actively transported probes (L-arabinose MW 150.1, L-rhamnose MW 164.2, perseitol MW 212.2 and lactulose MW=342.3) with increasing molecular weight (MW) to test for size dependency of the passive absorption. Probes were gavaged into the stomach dissolved in a 350 mosm solution. Plasma probe concentrations were then measured in serial blood samples. The carbohydrates were also injected into the pectoralis to estimate probe elimination constants. Bioavailability was calculated as F=[AUC by gavage)]/[AUC by injection] (AUC = area under the curve of plasma probe concentration vs. time). Bioavailability declined linearly with probe size a total of 80% from the smallest to the largest probe. Absorption of all the probes was enhanced when measured in the presence of luminal glucose or food, as compared with mannitol control. These findings suggest that passive paracellular absorption across the small intestine varies inversely with the size of the probes and that the presence of D-glucose and nutrients in the lumen of the small intestine enhances the absorption. Supported by FONCYT (01-03101) to EC-V and NSF (IBN-9723793) to WHK.