Histologic confirmation of microvascular hyperpermeability to macromolecular MR contrast medium in reperfused myocardial infarction

A macromolecular MR contrast medium (MMCM) designed to permit histochemical staining and specific tissue localization, albumin-(biotin) 10-(Gd-DTPA)25 (Bio-Alb-Gd), was used in a rat model of reperfused myocardial infarction to confirm the presence and distribution of microvascular hyperpermeability . T1-weighted spin-echo images were acquired before and after administratio n of Bio-Alb-Gd, An avidin-biotin-complex (ABC) stain, specific for the bio tinylated MR contrast medium, was used to define the MMCM distribution and to detect any regional change in microvascular permeability related to infa rction, Immediately after Bio-Alb-Gd administration, the infarcted region w as enhanced, with greatest signal intensity noted at the rim and less at th e center. There was a gradual increase in signal intensity of the initially hypointense central region. The steady increase in signal intensity of the central region suggested convection transport of MMCM through the intersti tial space and its influx into cellular compartment after leakage from the vascular compartment. Histologic findings confirmed regional microvascular hyperpermeability corresponding to the site of infarction and a predominant rim distribution of the MMCM. Bio-Alb-Gd was identified at high microscopi c power in the intravascular, interstitial, and intracellular spaces at the periphery of reperfused infarcted myocardium, Bio-Alb-Gd can be used as an MR contrast medium in reperfused infarcted myocardium to confirm the exist ence and to localize altered microvascular permeability to macromolecules. Bio-Alb-Gd contrast technique removes all the ambiguity between the distrib ution of the MR or other imaging contrast agent and the distribution of the substrate for histochemical staining.