title: Age dependency of vasopressin pulmonary vasodilatory effect in rats.
abstract: BACKGROUND
  Vasopressin is a systemic vasoconstrictor. Its pulmonary vasodilatory effect is controversial, and limited data are available on its use in neonates with pulmonary hypertension. Hypothesizing that the vasopressin-induced pulmonary vasodilation is developmentally regulated, we evaluated its pulmonary and systemic arterial response in newborn and adult rats.
  
  
  METHODS
  Vessels were mounted on a wire myograph, and the vasopressin-induced changes in vasomotor tone measured. The vessel- and age-dependent differences in vasopressin V1a and V2 receptors' expression were evaluated by western blotting.
  
  
  RESULTS
  Vasopressin induced a dose-dependent increase in mesenteric arterial tone at both ages, but of greater magnitude in adult vessels (P < 0.01). At lower concentrations, vasopressin induced pulmonary vasodilation in adult vessels and vasoconstriction in newborn arteries. The adult vasopressin-induced pulmonary vasodilation was inhibited by ibuprofen, suggesting that the response is prostaglandin mediated. Pulmonary tissue V1a receptor protein expression was higher in adult, when compared with newborn arteries (P < 0.01). The adult vessels V1a expression predominated in the pulmonary arteries, and V2 was only detected in mesenteric arteries.
  
  
  CONCLUSIONS
  The vasopressin-induced pulmonary vasodilation is absent in newborn rats likely due to the lower tissue V1a expression early in life. These animal data challenge the therapeutic use of vasopressin in neonatal pulmonary hypertension.
authors.affiliation: Department of Paediatrics, The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Enomoto
authors.affiliation: Department of Paediatrics, The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Jingyi
authors.initials: J
authors.lastname: Pan
authors.affiliation: Department of Paediatrics, The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Yulia
authors.initials: Y
authors.lastname: Shifrin
authors.affiliation: Department of Paediatrics, The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Jaques
authors.initials: J
authors.lastname: Belik
mesh_terms: D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D001158:Arteries / Q000473:pathology; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D006976:Hypertension, Pulmonary / Q000188:drug therapy* / Q000473:pathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D014665:Vasodilator Agents / Q000737:chemistry*; D014667:Vasopressins / Q000737:chemistry*
chemical_list: D014665:Vasodilator Agents; D014667:Vasopressins