title: Up and down-regulation of phosphodiesterase-5 as related to tachyphylaxis and priapism.
abstract: OBJECTIVE
  We identify whether tachyphylaxis and priapism effects of sildenafil are related to regulation of phosphodiesterase-5 (PDE-5) expression.
  
  
  METHODS
  Cavernous smooth muscle cells (CSMCs) were isolated from young rats and treated with 0, 1, 10 and 25 microM sildenafil with or without 100 microM of sodium nitroprusside for 3 and 7 days. The cells were subjected to reverse transcriptase-polymerase chain reaction and Western blot analysis for PDE-5 expression. Plasmid constructs carrying PDE-5A1 and PDE-5A2 promoters were transfected into COS-7 cells, treated with 25 microM sildenafil and analyzed for promoter activities. To simulate priapism, CSMCs were cultured under anoxia or hypoxia and then analyzed for PDE-5 expression. Furthermore, rats underwent bilateral pudendal arterial ligation for 1 day to 14 weeks, and corpus cavernous tissues were subjected to reverse transcriptase-polymerase chain reaction analysis for PDE-5 expression.
  
  
  RESULTS
  Up-regulation of PDE-5 was noted in CSMCs treated with 25 microM sildenafil for 7 days. PDE-5 messenger RNA and protein levels were significantly increased in the 7-day sildenafil treated cultures. Sodium nitroprusside appeared to down-regulate PDE-5 expression. Sildenafil significantly increased the activities of PDE-5A1 promoter. PDE-5 expression was significantly reduced under anoxia and hypoxia. The corpus cavernous tissue showed a gradual decrease in PDE-5 expression under ischemia.
  
  
  CONCLUSIONS
  Repeated treatment with sildenafil at high concentrations was needed to simulate tachyphylaxis in our cell culture system. Adequate oxygenation was important for PDE-5 expression. Thus, sicklemic patients may express PDE-5 at abnormally low levels, predisposing them at risk of stuttering priapism.
authors.affiliation: Department of Urology, Knuppe Molecular Urology Laboratory, University of California School of Medicine, San Francisco, CA 94143-1695, USA.
authors.forename: Guiting
authors.initials: G
authors.lastname: Lin
authors.forename: Zhong-Cheng
authors.initials: ZC
authors.lastname: Xin
authors.forename: Tom F
authors.initials: TF
authors.lastname: Lue
authors.forename: Ching-Shwun
authors.initials: CS
authors.lastname: Lin
mesh_terms: D015106:3',5'-Cyclic-GMP Phosphodiesterases; D000818:Animals; D002478:Cells, Cultured; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; D015536:Down-Regulation / Q000502:physiology; D008297:Male; D010410:Penile Erection / Q000187:drug effects / Q000502:physiology*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D010879:Piperazines / Q000494:pharmacology*; D011317:Priapism / Q000503:physiopathology*; D011687:Purines; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000068677:Sildenafil Citrate; D013450:Sulfones; D013618:Tachyphylaxis; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology
chemical_list: D010726:Phosphodiesterase Inhibitors; D010879:Piperazines; D011687:Purines; D013450:Sulfones; D000068677:Sildenafil Citrate; D010727:Phosphoric Diester Hydrolases; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; C517384:Pde5a protein, rat