MRI Methods for Imaging Beta-Cell Function in the Rodent Pancreas

Abstract

The role of Zn²⁺ ions in proper storage of insulin in β-cell granules is well-established so when insulin is secreted from β-cells stimulated by an increase in plasma glucose, free Zn²⁺ ions are also released. This local increase in Zn²⁺ can be detected in the pancreas of rodents in real time by the use of a zinc-responsive MR contrast agent. This method offers the opportunity to monitor β-cell function longitudinally in live rodents. The methods used in our lab are fully described in this short report and some MR images of a rat pancreas showing clearly enhanced hot spots in the tail are presented.

Keywords: Functional imaging; Glucose-stimulated insulin secretion (GSIS); Glucose-stimulated zinc secretion (GSZS); Imaging β-cell function in vivo; MRI; Rodent models; Zinc-responsive agents.

Fig. 1

A diagram of a home built rat holder for an animal MR scanner

Fig. 2

The chemical structures of two slightly differenct zinc-responsive MR contrast agents. The higher affinity agent, GdL1, was used in the experiment described here

Fig. 3

T1-weighted 2D gradient echo multi-slice (GEMS) MR images though the rat abdomen containing a portion of pancreatic tissue. Panel (a), shows an axial slice through a rat abdomen at baseline. Panel (b) was obtained from the same location, but after the injection of GdL1 plus glucose. Panels (c) and (d) are colorized and zoomed versions of panels (a) and (b), respectively, for easier visualization of the pancreatic hot spots thought to represent individual islets. Regions of interest (ROIs) on the target organ (pancreatic tail), phantom, and background are shown in black, red, and blue, respectively