The efficacy of density gradients for islet purification: a comparison of seven density gradients.

Seven different density gradient-forming materials were compared as to their efficacy for rat islet purification. Continuous density gradients were used in order to determine the bouyant densities of the different pancreatic tissue components. Hand-picked islets served as a control. A significant separation of large numbers of islets from the exocrine tissue band was only seen in the albumin, dextran-40, and metrizamide gradients. Pure islet preparations could not be obtained with any of the gradients studied as none of the gradients completely separated lymph nodes, vessels, and ducts from the islets. Gradients containing sucrose resulted in low islet yields. The islet yields obtained with the other gradients were in the same range as those obtained by hand-picking. Metrizamide gave significantly higher yields than the widely used Ficoll. Judged both in terms of numbers of islets and their in vitro function, the best results were obtained with metrizamide and dextran-40.