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Abstract
1. Biliary excretion in biliary-cannulated female rats of 23 derivatives of sulphanilamide, in which the N4-position is substituted with various carboxyacyl groups and the N1-position with acetyl or 2-thiazole, has been studied.
2. Six compounds having molecular weights in the range 172–314 were poorly excreted in the bile (<5% of dose) but seventeen others (mol. wt. range 319–719) were eliminated in the bile to an appreciable extent (7–74%). For the compounds studied there appears to be a threshold value for the mol. wt. (320–370) at and above which biliary excretion becomes appreciable (>5–10% of dose).
3. Above the threshold mol. wt., biliary excretion is high (20–70% of dose) but there is no direct relationship between the two, as the extent of biliary excretion is not directly proportional to mol. wt.
4. There is no direct relationship between the extent of biliary excretion and the relative lipid solubilities as measured by distribution ratios between buffer pH 7.4 and organic solvents. Nevertheless there is a general trend for compounds which are extensively eliminated in the bile to be more lipophilic than those that are not excreted in the bile.
5. Above the threshold mol. wt. marked variations in the extent of biliary excretion of compounds having similar mol. wt. can occur. These variations can be attributed to the influence of a ‘structural factor’ in biliary excretion. This factor could affect the lipid solubility or the shape of the molecule.