Key Points
- To determine whether blood vessels in the intact, beating heart possess specific insulin receptors and to identify their precise cellular and microvascular location.
- Perfused intact beating hearts with [125I]iodoinsulin (3 × 10^-10 M) followed by perfusion or coperfusion with unlabeled insulin (10^-11 M to 10^-6 M), proinsulin, or unrelated peptide controls.
- Quantified kinetic hormone displacement and anatomical grain distribution across cardiac vessels using light and electron microscopic radioautography.
- Unlabeled insulin displaced bound [125I]iodoinsulin in direct proportion to concentration, beginning at 10^-11 M with maximal displacement at 10^-6 M, whereas proinsulin showed 1% of insulin potency and unrelated peptides showed no effect.
- Light radioautography demonstrated that greater than 95% of vessel grain counts localized to microvessels, which electron microscopy confirmed were associated directly with vascular endothelial cells.
- Perfusion with 10^-6 M unlabeled insulin following [125I]iodoinsulin reduced microvascular grain counts by 50%, while coperfusion reduced grain counts by 80% relative to [125I]iodoinsulin alone.
Structured PICO
PPopulationIntact, beating hearts
IInterventionPerfusion with [125I]iodoinsulin (3 X 10(-10) M) followed by perfusion with unlabeled insulin or proinsulin
CComparatorPerfusion with [125I]iodoinsulin alone or unrelated peptides
OOutcomeDisplacement of bound [125I]iodoinsulin and localization of 125I grainssurrogate
Demonstrates the presence of specific insulin receptors on the endothelial cells of microvessels in the intact heart.