Abstract
BackgroundOur previous research and other studies with radiotracers showed evidence of a centripetal drainage pathway, separate from blood or lymphatic vessels, that can be visualized when a small amount of low molecular weight tracer is injected subcutaneously into a given region on skin of humans. In order to further characterize this interesting biological phenomenon, animal experiments are designed to elucidate histological and physiologic characteristics of these visualized pathways.MethodsMultiple tracers are injected subcutaneously into an acupuncture point of KI3 to visualize centripetal pathways by magnetic resonance imaging or fluorescein photography in 85 healthy rabbits. The pathways are compared with venography and indirect lymphangiography. Fluid flow through the pathways is observed by methods of altering their hydrated state, hydrolyzing by different collagenases, and histology is elucidated by optical, fluorescein and electron microscopy.ResultsHistological and magnetic imaging examinations of these visualized pathways show they consist of perivenous loose connective tissues. As evidenced by examinations of tracers’ uptake, they appear to function as a draining pathway for free interstitial fluid. Fluorescein sodium from KI3 is found in the pathways of hind limbs and segments of the small intestines, partial pulmonary veins and results in pericardial effusion, suggesting systematical involvement of this perivenous pathway. The hydraulic conductivity of these pathways can be compromised by the collapse of their fiber-rich beds hydrolyzed by either of collagenase type I, III, IV or V.ConclusionsThe identification of pathways comprising perivenous loose connective tissues with a high hydraulic conductivity draining interstitial fluid in hind limbs of a mammal suggests a potential drainage system complementary to vascular circulations. These findings may provide new insights into a systematically distributed collagenous connective tissue with a circulatory function and their potential relevance to the nature of acupuncture meridians.
Highlights
The search for the anatomical and histological structures of the ancient meridians has continued for decades
The pathways displayed by Gd-DTPA are the same pathways visualized by the fluorescein sodium when comparing the reconstructed images by MRI with the photos by digital camera (Figs. 1A1–1A2, Figure S1B1–S1D3)
These illustrated pathways originating from KI3 coincide with the Greater Saphenous Vein (GSV), Saphenous Vein (SSV), and their respective main branches located in the hind limbs as well as the inferior vena cava (IVC), vertebral veins (VV), aorta (AO) and pulmonary arteries (PA) in the intra-abdominal and intra-thoracic cavities
Summary
The search for the anatomical and histological structures of the ancient meridians has continued for decades Trying to identify their scientific basis, previous studies have anatomically revealed neural pathways, connective tissue facial planes, collagen fiber bands [1] and Bonghan ducts (BHDs) [2]. In parallel with the neural hypothesis, since 1980s, several studies [5,6,7] have demonstrated an interesting biological phenomenon in which a linear migration pathway of interstitial fluid within loose connective tissue is visualized by injecting a low molecular weight (MW) radiotracer subcutaneously, usually at an acupuncture point. In order to further characterize this interesting biological phenomenon, animal experiments are designed to elucidate histological and physiologic characteristics of these visualized pathways
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