Transfer of exogenous macromolecules from rat stomach wall to blood and lymph is dependent on molecular weight

Transfer selectivity to the blood and the lymph of exogenous dextrans of various average molecular weight (approximate 4, 10, 18, 39 and 70 kilodaltons (kDa)) after dosing to the subserosal layer of the rat stomach wall was investigated by measuring the fluorescein isothiocyanate labelled dextran concentrations in the lymph of the thoracic duct and the peripheral plasma. The lymph/plasma level ratio of the dextrans rose greatly with the increase in molecular weight (over 10kDa) owing largely to the lower plasma concentration, although the lymph levels of small dextran (4kDa) were not significantly higher than the plasma levels. These results indicate that there is an inverse relation between plasma levels of dextrans and their molecular weight, and also suggest that the molecular weight threshold of transfer selectivity of dextran to the blood and the lymph administered in the rat stomach wall is between 4-10 kDa.