title: Fluid flow along venous adventitia in rabbits: is it a potential drainage system complementary to vascular circulations?
abstract: BACKGROUND
  Our 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.
  
  
  METHODS
  Multiple 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.
  
  
  RESULTS
  Histological 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.
  
  
  CONCLUSIONS
  The 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.
authors: Cardiology Division, Beijing Hospital of the Ministry of Health, Beijing, People's Republic of China. godspeedlhy@gmail.com
authors: Hong-yi
authors: HY
authors: Li
authors: Min
authors: M
authors: Chen
authors: Jie-fu
authors: JF
authors: Yang
authors: Chong-qing
authors: CQ
authors: Yang
authors: Liang
authors: L
authors: Xu
authors: Fang
authors: F
authors: Wang
authors: Jia-bin
authors: JB
authors: Tong
authors: You
authors: Y
authors: Lv
authors: Caidan
authors: C
authors: Suonan
mesh_terms: D063194:Adventitia / Q000000981:diagnostic imaging / Q000502:physiology* / Q000648:ultrastructure; D000818:Animals; D001775:Blood Circulation / Q000502:physiology*; D019793:Fluorescein / Q000494:pharmacology; D006801:Humans; D042601:Lymphatic Vessels / Q000000981:diagnostic imaging / Q000502:physiology* / Q000648:ultrastructure; D018810:Magnetic Resonance Angiography; D011817:Rabbits; D011849:Radioactive Tracers; D011859:Radiography; D014680:Veins / Q000502:physiology* / Q000648:ultrastructure
chemical_list: D011849:Radioactive Tracers; D019793:Fluorescein