title: An adenosine agonist increases blood flow and density of capillary branches in the optic tectum of Xenopus laevis tadpoles.
abstract: OBJECTIVE
  To test the hypothesis that adenosine can increase capillary densities in developing brain tissue.
  
  
  METHODS
  Transparent tadpoles of albino Xenopus laevis were exposed to adenosine agonists, mainly 5'-N-ethylcarboxamidoadenosine (NECA), and to antagonists, mainly 8-phenyltheophylline (8PT) in aquarium water. After 2 weeks in drugs, networks of blood vessels on the dorsal surface of the optic tectum were scanned in vivo by videomicroscopy. Densities of surface capillaries and venules, of deep branches, and of deep perfused capillaries were calculated.
  
  
  RESULTS
  NECA initially dilated brain blood vessels and chronically increased blood flow by a simple subjective index. 8PT diminished diameters and prevented the subjective flow increase. Chronic 3 microM NECA significantly increased densities of total deep branches from pial vessels into the tectum.
  
  
  CONCLUSIONS
  In an in vivo amphibian assay, NECA dilated brain capillaries and venules and increased their flow and density. Adenosine was present chemically and increased during metabolic stress. These results are consistent with adenosine as a metabolic signal for growth of blood vessels during brain development. In addition, it appeared that short-term dilation and flow increase in tectal capillaries in acute NECA was followed over a period of weeks in chronic NECA by vascular remodeling and return of diameters to normal.
authors.affiliation: Department of Cell Biology and Physiology, Washington University Medical School, St. Louis, Missouri, USA.
authors.forename: S C
authors.initials: SC
authors.lastname: Jen
authors.forename: C M
authors.initials: CM
authors.lastname: Rovainen
mesh_terms: D000241:Adenosine / Q000819:agonists* / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000494:pharmacology; D019830:Adenosine-5'-(N-ethylcarboxamide); D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002196:Capillaries / Q000187:drug effects; D008833:Microcirculation / Q000187:drug effects; D018715:Microscopy, Video; D018919:Neovascularization, Physiologic / Q000187:drug effects*; D005996:Nitroglycerin / Q000494:pharmacology; D012039:Regional Blood Flow / Q000187:drug effects; D013477:Superior Colliculi / Q000098:blood supply* / Q000187:drug effects; D013806:Theophylline / Q000031:analogs & derivatives / Q000494:pharmacology; D013997:Time Factors; D014665:Vasodilator Agents / Q000494:pharmacology; D014982:Xenopus laevis
chemical_list: D014665:Vasodilator Agents; D019830:Adenosine-5'-(N-ethylcarboxamide); C027513:N(6)-cyclohexyladenosine; D002110:Caffeine; D013806:Theophylline; C028322:8-phenyltheophylline; D005996:Nitroglycerin; D000241:Adenosine