Male Wistar rats (6 weeks, 250g), (Charles River, Sulzfeld, Germany) were equipped with micro osmotic pumps model 2001 from Alzet (Cupertino, CA) containing 400mM PETN dissolved in DMSO or the solvent and infusion was maintained for four days at 1?l/h (10.5?g/kg/min). For direct comparison, rats were also infused with 450mM NTG (6.6?g/kg/min in ethanol or the solvent as a control).