Fluid Flow along Venous Adventitia in Rabbits: Is It a Potential Drainage System Complementary to Vascular Circulations?

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.

Longitudinal non-vascular transport pathways originating from acupuncture points in extremities visualised in human body

“…In summary, the behaviours of the imaging tracers strongly suggested that specific anatomical structures located within the subcutaneous tissues or the partial walls of some veins are unique transport pathways that originate from the subcutis of anatomical extremities and possibly connect with certain ''internal organs'', as was previously described in rabbits [6]. We believe that the challenge of developing more techniques for the detection of longitudinal non-vascular transport pathways within the extremities, various organs in splanchnocoele and even within the Centrifugal and centripetal transport of the fluorescein injected into LU9 (a-c) and (d-f).…”

“…To the best of our knowledge, neither anatomical nor histological knowledge can explain this phenomenon in humans. Notably, we have reported that the perivenous loose connective tissues (including the venous adventitia) of vascular trees can transport interstitial fluid from extremities into pericardial cavities in rabbits, which might offer valuable insight into the precise histological structures of the enhanced ''partial walls of veins'' in humans [6].…”

“…However, in studies investigating ancient meridian pathways by injecting various low molecular weight tracers within specific regions of the skin (generally acupuncture points), non-vascular drainage pathways can be visualised in animals as well as in humans [1][2][3][4][5]. In animals, these pathways, which conform to the perivenous loose connective tissues (PLCTs) along venous trees (including the venous adventitia), are capable of draining free fluid [6]. With regards to humans, two types of transport pathways have been visualised by injecting paramagnetic tracers into acupuncture points using magnetic resonance imaging (MRI) [5].…”

“…The first type is the superficial venous plexus, and the second is ''puncture-resistant'' subcutaneous transport pathways (STPs) which is different in nature from tubular lymphatics with the endothelial walls, although the superficial appearance of the subcutaneous pathways is similar to those of lymphatic vessels visualised by indirect MR lymphography in patients with lymphedema [7]. Are these subcutaneous transport pathways in humans composed of the connective tissues like the previously reported PLCTs in a mammal [6]? Due to the difficulties in directly obtaining histological data from humans, we continue to study these transport pathways using imaging techniques and hope to facilitate the identification of the anatomical and histological structures of these specific transport pathways in humans eventually.…”

Active interfacial dynamic transport of fluid in a network of fibrous connective tissues throughout the whole body

“…At the same time, the peripheral fluorescent ISF was found in the walls of segmental small intestines and right pulmonary veins as well, which indicated that there was probably more than one centre of IDT driving powers in physiological conditions. The measured speed of venous adventitial ISF flow was around 0.2‐2 cm/s in the rabbit . By Doppler technique, the measured speed of femoral arterial blood flow in the rabbit was around 5‐50 cm/s and the femoral venous blood flow was around 6‐7 cm/s .…”