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There is an obvious and growing medical need for an accurate and easy to handle determination of glomerular filtration rate (GFR) for a broad spectrum of indications. Newly synthesized fluorescein-isothiocyanate (FITC)-sinistrin (FS) with various degrees of labeling was selected by its physicochemical properties and good tolerability out of a number of dye-labeled compounds intended for use as GFR markers for characterization of its pharmacological profile. With respect to solubility FS is more convenient in handling compared to FITC-inulin (FI). Up to 100 mg ml(-1) of FS can be dissolved in aqueous solvents at room temperature, whereas FI can only be solubilized after warming up to 55 degrees C. This reveals a considerable advantage of FS over FI in preparation of galenical formulations for intended i.v. application. A fluorometric method was established to determine FS concentration in blood serum with a comparable accuracy to the established enzymatic method for polyfructosanes. Similar concentration time curves in blood serum of FS measured fluorometrically and enzymatically suggest no relevant change of pharmacokinetic behavior by dye labeling. This notion is supported by the rapid renal and missing of biliary excretion. On the basis of these results, FS is superior in handling to the available GFR markers and makes it highly interesting as a novel diagnostic drug.

In screening experiments certain ω-substituted alkyl carboxylic acids, were found to produce an increase in insulin-stimulated 14C-acetate incorporation into triglycerides, which may indicate an improvement in the action of insulin. Antidiabetic and lipid-lowering properties in genetically diabetic ob/ob mice demonstrated the in vivo relevance of the insulin-potentiating effects seen in vitro. The chemical structures of the ω-substituted alkyl carboxylic acids with insulin-potentiating effects correspond to the general formula ring-spacer-COOH. A close structure-activity relationship was observed. The most potent compound in ob/ob mice was 3e, which normalized blood glucose as well as hyperinsulinaemia and lowered serum triglycerides and cholesterol by 52% and 37%, respectively. On the basis of these results, ω-substituted alkyl carboxylic acids are interesting as a new class of oral antidiabetic agents with insulin-sensitizing and lipid-lowering activity.