title: A physiological solvent for crystalline insulin.
abstract: Insulin is insoluble in water at physiological pH, but dissolves relatively rapidly in plasma. To quantify the ability of various solutions to dissolve crystalline insulin, a simple assay measuring dissolution time was developed. At pH 7.5 and room temperature, distilled water, 0.154 mol/l NaCl, Ringer's lactate solution, and 5% albumin in 0.154 mol/l NaCl did not dissolve insulin crystals within 30 min. Normal postprandial human plasma and a protein-free cell culture medium dissolved insulin crystals within 3 to 8 min. This ability was inhibited by acid titration of the fluids to a stable pH of 6.30, at which point bicarbonate depletion could be implied. Repletion of bicarbonate did restore the ability of these solutions to dissolve insulin crystals, but back-titration to the initial pH with NaOH did not. The effect of sodium bicarbonate alone was strongly concentration dependent above 23 mmol/l. We suggest that the ability of physiological fluids to dissolve insulin crystals at normal pH depends on their bicarbonate content. The ability to dissolve insulin with a physiological solvent which prevents its reaggregation promises to facilitate its use in portable pumping systems.
mesh_terms: D000328:Adult; D001639:Bicarbonates / Q000097:blood; D055598:Chemical Phenomena; D002621:Chemistry; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007328:Insulin; D008297:Male; D010949:Plasma; D012997:Solvents
chemical_list: D001639:Bicarbonates; D007328:Insulin; D012997:Solvents