title: The effect of vasopressin on ciliary blood flow and aqueous flow.
abstract: OBJECTIVE
  Previous experiments have shown that arginine-vasopressin (AVP) reduces intraocular pressure (IOP) dose-dependently. The present study investigated the relationships between IOP, ciliary blood flow (CilBF), and aqueous flow (AqF) responses to AVP in anesthetized rabbits.
  
  
  METHODS
  CilBF was measured by laser Doppler flowmetry and AqF by fluorophotometry. Mean arterial pressure (MAP) and IOP were monitored continuously and simultaneously. Perfusion pressure (PP) was varied mechanically. Four experimental protocols were performed: the dose-response (n = 11) and the pressure-flow relationship (n = 8) for CilBF and the effects on CilBF, and AqF at low (0.08 ng/kg/min; n = 14) and high AVP infusion rates (1.33 ng/kg/min; n = 12).
  
  
  RESULTS
  AVP decreased CilBF and IOP dose-dependently. At the low AVP infusion rate, AqF was reduced by 21.48% ± 2.52% without changing CilBF significantly. The high AVP infusion rate caused a 24.49% ± 3.53% decrease of AqF and a significant reduction in CilBF (35.60% ± 3.58%). IOP was reduced by 9.56% ± 2.35% at low and by 41.02% ± 3.19% at high AVP infusion rates. Based on the Goldmann equation, the decrease of AqF at the low AVP infusion rate accounted for 77.1% of the IOP reduction, whereas at the high AVP infusion rate, decreased AqF accounted for 28.4% of the IOP decline.
  
  
  CONCLUSIONS
  The results indicate that AVP can modulate IOP by different dose-dependent physiological mechanisms. The shifts of the CilBF-AqF relationship suggest that the reduction of AqF by the low AVP infusion rate is mainly provoked by inhibiting secretory processes in the ciliary epithelium. In contrast, at the high AVP infusion rate, the AqF reduction is caused by either reduced CilBF or more likely by a combined effect of reduced CilBF and secretory inhibition.
authors: Department of Ophthalmology and Optometry and Research Program for Experimental Ophthalmology, SALK/Paracelsus Medical University, Salzburg, Austria.
authors: Barbara
authors: B
authors: Bogner
authors: Christian
authors: C
authors: Runge
authors: Clemens
authors: C
authors: Strohmaier
authors: Andrea
authors: A
authors: Trost
authors: Birgit
authors: B
authors: Tockner
authors: Jeffrey W
authors: JW
authors: Kiel
authors: Falk
authors: F
authors: Schroedl
authors: Herbert A
authors: HA
authors: Reitsamer
mesh_terms: D000818:Animals; D001082:Aqueous Humor / Q000187:drug effects / Q000502:physiology*; D002924:Ciliary Body / Q000098:blood supply* / Q000378:metabolism; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D005260:Female; D015590:Fluorophotometry; D005901:Glaucoma / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology; D007262:Infusions, Intravenous; D007429:Intraocular Pressure / Q000187:drug effects*; D017078:Laser-Doppler Flowmetry; D008297:Male; D011817:Rabbits; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology*; D014662:Vasoconstrictor Agents / Q000008:administration & dosage / Q000493:pharmacokinetics; D014667:Vasopressins / Q000008:administration & dosage* / Q000493:pharmacokinetics
chemical_list: D014662:Vasoconstrictor Agents; D014667:Vasopressins
keywords: aqueous flow; aqueous humor production; ciliary blood flow; vasopressin