Effects of sildenafil on cardiopulmonary responses during stress

Effects of acute phosphodiesterase type 5 inhibition on skeletal muscle interstitial PO2 during contractions and recovery

The oxygen partial pressure within the interstitial space (PO2is; mmHg) provides the driving force for oxygen diffusion into the myocyte thereby supporting oxidative phosphorylation. We tested the hypothesis that potentiation of the nitric oxide pathway with sildenafil (phosphodiesterase type 5 inhibitor) would enhance PO2is during muscle metabolic transitions, thereby slowing PO2is on- and accelerating PO2is off-kinetics. The rat spinotrapezius muscle (n = 17) was exposed for PO2is measurements via phosphorescence quenching under control (CON), low-dose sildenafil (1 mg/kg i.a., SIL1) and high-dose sildenafil (7 mg/kg i.a., SIL7). Data were collected at rest and during submaximal twitch contractions (1 Hz, 4-6 V, 3 min) and recovery (3 min). Mean arterial blood pressure (MAP; mmHg) was reduced with both SIL1 (pre:132 ± 5; post:99 ± 5) and SIL7 (pre:111 ± 6; post:99 ± 4) (p < 0.05). SIL7 elevated resting PO2is (18.4 ± 1.1) relative to both CON (15.7 ± 0.7) and SIL1 (15.2 ± 0.7) (p < 0.05). In addition, SIL7 increased end-recovery PO2is (17.7 ± 1.6) compared to CON (12.8 ± 0.9) and SIL1 (13.4 ± 0.8) (p < 0.05). The overall PO2is response during recovery (i.e., area under the PO2is curve) was greater in SIL7 (4107 ± 444) compared to CON (3493 ± 222) and SIL1 (3114 ± 205 mmHg s) (p < 0.05). Contrary to our hypothesis, there was no impact of acute SIL (1 or 7 mg/kg) on the speed of the PO2is response during contractions or recovery (p > 0.05). However, sildenafil lowered MAP and improved skeletal muscle interstitial oxygenation in healthy rats. Specifically, SIL7 enhanced PO2is at rest and during recovery from submaximal muscle contractions. Potentiation of the nitric oxide pathway with sildenafil enhances microvascular blood-myocyte O2 transport and is expected to improve repeated bouts of contractile activity.

The effect of cardioplegic supplementation with sildenafil on cardiac energetics in a piglet model of cardiopulmonary bypass and cardioplegic arrest with warm or cold cardioplegia

Cardioplegic cardioprotection strategies used during paediatric open-heart surgery remain suboptimal. Sildenafil, a phosphodiesterase 5 (PDE-5) inhibitor, has been shown to be cardioprotective against ischemia/reperfusion injury in a variety of experimental models and this study therefore tested the efficacy of supplementation of cardioplegia with sildenafil in a piglet model of cardiopulmonary bypass and arrest, using both cold and warm cardioplegia protocols. Piglets were anaesthetized and placed on coronary pulmonary bypass (CPB), the aorta cross-clamped and the hearts arrested for 60 min with cardioplegia with or without sildenafil (10 nM). Twenty minutes after removal of cross clamp (reperfusion), attempts were made to wean the pigs from CPB. Termination was carried out after 60 min reperfusion. Throughout the protocol blood and left ventricular tissue samples were taken for analysis of selected metabolites (using HPLC) and troponin I. In both the cold and warm cardioplegia protocols there was evidence that sildenafil supplementation resulted in faster recovery of ATP levels, improved energy charge (a measure of metabolic flux) and altered release of hypoxanthine and inosine, two purine catabolites. There was no effect on troponin release within the studied short timeframe. In conclusion, sildenafil supplementation of cardioplegia resulted in improved cardiac energetics in a translational animal model of paediatric CPB surgery.

Sildenafil may facilitate weaning in mechanically ventilated COPD patients: a report of three cases

We report three cases of mechanically ventilated chronic obstructive pulmonary disease patients who were intubated due to an exacerbation of their disease and who presented with repeated spontaneous breathing trial failures. Patients were given 50 mg of sildenafil through the nasogastric tube, under close monitoring of haemodynamic and ventilatory parameters. After sildenafil, pulmonary artery pressure, pulmonary artery occlusion pressure, the respiratory frequency to tidal volume ratio and the P(a)CO2-P(ET)CO2 (arterial minus end-tidal carbon dioxide pressure) decreased. Cardiac output increased in two of the patients, while all of them were successfully extubated. This is the first report of successful extubation after sildenafil use.

ORIGINAL RESEARCH—ERECTILE DYSFUNCTION: Erectile Dysfunction Severity Might be Associated with Poor Cardiovascular Prognosis in Diabetic Men

INTRODUCTION

Although erectile dysfunction (ED) might be associated with coronary heart disease (CHD), there is no evidence it predicts poor cardiovascular prognosis. On the other hand, an abnormal heart rate profile during exercise stress testing predicts poor cardiovascular prognosis in high-risk patients, such as diabetic men, even in the absence of CHD.

AIM

In order to study if ED predicts poor cardiovascular prognosis in high-risk patients, we examined the association between ED and heart rate profile during exercise stress testing in diabetic men with no CHD.

MAIN OUTCOME MEASURES

Erectile dysfunction severity, exercise capacity during exercise stress testing, and heart rate decrease after exercise stress testing.

METHODS

A retrospective study. The medical charts of diabetic men with vascular ED from a single-sex clinic were reviewed, as well as the medical charts of body mass index (BMI)- and age-matched diabetic men without ED going through routine check-ups. All men underwent routine treadmill stress testing according to the Bruce protocol in order to characterize heart rate profile during exercise. The Sexual Health Inventory for Men (SHIM) questionnaire was used to characterize ED.

RESULTS

Included were 18 diabetic men with ED (SHIM questionnaire scores 5-21) and 18 diabetic men without ED (SHIM questionnaire scores 22-25), 40 years of age or older. None of the men had signs of coronary insufficiency during exercise treadmill stress testing. Although the two groups did not statistically differ with respect to the mean age, the mean BMI, the prevalence of cardiovascular risk factors, and the mean exercise treadmill stress testing findings, the SHIM questionnaire scores were significantly associated with low metabolic equivalents (r = 0.51, P = 0.03) and delayed heart rate recovery during the first 2 minutes after exercise (r = 0.55, P = 0.018) only among diabetic men with ED.

CONCLUSIONS

Erectile dysfunction severity might be associated with poor cardiovascular prognosis in adult diabetic men with no CHD.

Sildenafil: Emerging Cardiovascular Indications

The discovery in 1989 of sildenafil, a highly selective inhibitor of phosphodiesterase-5 (PDE-5), was the result of extensive research on chemical agents targeting PDE-5 that might potentially be useful in the treatment of coronary heart disease. Initial clinical studies on sildenafil in the early 1990s were not promising with respect to its antianginal potential. However, the incidental discovery of its antiimpotence effect led to its approval of for the treatment of erectile dysfunction. Thereafter, several reports of adverse cardiac events in patients on sildenafil raised concerns about its safety in cardiovascular disorders. Novel therapeutic indications are emerging for sildenafil with the recent discovery that PDE-5 is expressed in various other tissues such as the arterial vasculature, including pulmonary and coronary arteries, venous vasculature, skeletal muscles, platelets, and visceral and tracheobronchial muscles. In this review we briefly summarize the pharmacology of sildenafil and the current available evidence on its potential therapeutic applications in cardiovascular disorders.