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Transmural hematocrit gradient in left ventricular myocardia of rats
1Institut National de la Santé et de la Recherche Médicale, U141, Hospital Lariboisière, Paris, France.
Insights
Tissue hematocrit, a measure of red blood cell concentration in heart muscle, decreases from the outer to inner layers of the rat left ventricle. This hematocrit gradient exists in both relaxed and contracted heart states.
Area of Science:
- Cardiovascular Physiology
- Biomedical Engineering
- Myocardial Metabolism
Background:
- Understanding the transmural distribution of blood components within the myocardium is crucial for comprehending oxygen and nutrient delivery.
- Previous studies have suggested heterogeneity in myocardial blood flow and composition, but detailed transmural hematocrit gradients remain incompletely characterized.
Purpose of the Study:
- To quantify the transmural gradient of tissue hematocrit in the rat left ventricular myocardium.
- To investigate whether this gradient is influenced by the contractile state of the heart.
Main Methods:
- Utilized radiolabeled tracers: technetium-99m (99Tc) for red blood cells and iodine-131 (131I) for albumin.
- Measured intramyocardial distribution volumes in arrested rat hearts (relaxed via KCl, contracted via BaCl2).
- Employed serial en face sectioning of the left ventricular free wall from epicardium to endocardium for precise regional analysis.
Main Results:
- A significant, decreasing gradient of tissue hematocrit was observed from the subepicardial to the subendocardial layers in both relaxed and contracted states.
- Subendocardial tissue hematocrit was approximately 70% of the subepicardial value, indicating a substantial transmural gradient.
Conclusions:
- The rat left ventricular myocardium exhibits a distinct transmural gradient in tissue hematocrit, with lower values in the subendocardium.
- This gradient is present regardless of the heart's contractile state, suggesting an intrinsic structural or flow-related mechanism.
Abstract:
The transmural distribution of tissue hematocrit was determined in rat left ventricular myocardium. Intramyocardial distribution volumes of 99Tc-labeled red blood cells and 131I-labeled albumin were measured in hearts arrested in a relaxed state by KCl or in a contracted state by BaCl2. Hearts were frozen in situ immediately after arrest by bathing in a mixture of liquid nitrogen and isopentane. After excision of the heart, a parallelepipedic portion was cut in a transverse section of the left ventricular free wall and subjected to en face serial sectioning through the thickness of the wall from the epicardium to the endocardium. 99Tc and 131I activity allowed determination of red blood cell and plasma volume and consequently of tissue hematocrit in each section. In both the relaxed and the contracted states of the hearts, a significant decreasing gradient of tissue hematocrit was found from the outer to the inner layers of myocardium. Tissue hematocrit in the subendocardial layers was approximately 70% of its value in the subepicardial layers.
