Evaluation of metaiodobenzylguanidine heart and lung extraction fraction by first-pass analysis in pigs.

Abstract

Metaiodobenzylguanidine (MIBG) is a norepinephrine analog that can be used to study cardiac sympathetic innervation. Most of the kinetic data on MIBG, however, have been obtained in vitro from adrenal chromaffin cells. To elucidate MIBG cardiac kinetics in vivo, we measured the first-pass extraction fraction (EF) of MIBG in pig heart and lungs and determined the relationship between the cardiac EF and myocardial blood flow (MBF) before and after dipyridamole, cocaine and imipramine. The first-pass lung EF was 24% +/- 0.80% (mean +/- s.e.). The baseline cardiac EF of MIBG was 79% +/- 1.6%. With dipyridamole, MBF increase significantly and the EF fell (82% +/- 2.5% to 71% +/- 3.5% baseline compared to 0.03 mg/kg/min dipyridamole, p less than 0.001), indicating that the cardiac EF of MIBG is dependent on MBF. Cocaine infusion had no effect on MBF or EF. Imipramine caused a significant increase in the EF (72% +/- 3.5% versus 77% +/- 2.5%, baseline versus imipramine p = 0.032) without a change in MBF. In adrenal chromaffin cells, cocaine and imipramine decrease MIBG uptake, suggesting that adrenal chromaffin cells may be an inappropriate model for studying MIBG kinetics in cardiac sympathetic neurons.