title: Platelet activating factor (PAF) increases plasma protein extravasation and induces lowering of interstitial fluid pressure (P) in rat skin.
abstract: OBJECTIVE
  To investigate the ability of the microdialysis technique to measure capillary selectivity of different sized plasma proteins induced by local administration of platelet activating factor (PAF).
  
  
  METHODS
  We used hollow plasmapheresis fibres with 3 cm membrane (cut off 3000 kDa) placed on the back of anaesthetized rats.
  
  
  RESULTS
  Platelet activating factor (50 microg mL(-1)) administered locally via the fibre, increased extravasation of radiolabelled 125I-HSA from plasma to the microdialysis fibre by approximately 900% compared both to baseline and the control fibre within 70 min (n = 6, P < 0.05). The extravasation in the control fibre did not change over time. HPLC measurement of plasma proteins in the microdialysis perfusate also demonstrated decreased capillary selectivity for proteins in the diameter range of 73 A, 56 A and 39 A after local administration of PAF (n = 6, P < 0.05). PAF also significantly lowered interstitial fluid (P(if)) pressure after subcutaneous administration (50 microg mL(-1)). Mean arterial pressure (MAP) after intravenous injection of PAF (0.4 microg kg(-1)) fell instantly by about 50 mmHg, and stabilized at 50 mmHg after 15 min (n = 6). MAP was unaltered when PAF was given through the microdialysis fibre (n = 4). Both total tissue water (TTW) and extravasation of albumin, measured as the plasma-to-tissue clearance (E-alb) showed a significant increase after PAF (n = 7, P < 0.05).
  
  
  CONCLUSIONS
  The present study demonstrates that PAF induces plasma protein extravasation and decrease capillary selectivity of different sized plasma proteins. It also increases transcapillary fluid flux, and lowers P(if), indicating a role for PAF in the interstitium for generation of transcapillary transport of water and large molecules followed by formation of oedema.
authors.affiliation: Department of Biomedicine, Section for Physiology, University of Bergen, Bergen, Norway. vegard.iversen@fys.uib.no
authors.forename: V V
authors.initials: VV
authors.lastname: Iversen
authors.forename: T
authors.initials: T
authors.lastname: Nedrebø
authors.forename: B A
authors.initials: BA
authors.lastname: Borge
authors.forename: G S
authors.initials: GS
authors.lastname: Salvesen
authors.forename: R K
authors.initials: RK
authors.lastname: Reed
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D001798:Blood Proteins / Q000378:metabolism*; D002199:Capillary Permeability / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D045604:Extracellular Fluid / Q000187:drug effects* / Q000502:physiology; D005260:Female; D017551:Microdialysis / Q000379:methods; D010972:Platelet Activating Factor / Q000494:pharmacology*; D011312:Pressure; D019275:Radiopharmaceuticals; D051381:Rats; D017208:Rats, Wistar; D012711:Serum Albumin, Radio-Iodinated; D012867:Skin / Q000098:blood supply / Q000187:drug effects* / Q000378:metabolism
chemical_list: D001798:Blood Proteins; D010972:Platelet Activating Factor; D019275:Radiopharmaceuticals; D012711:Serum Albumin, Radio-Iodinated