Sildenafil augments early protective transcriptional changes after ischemia in mouse myocardium

Chronic Sildenafil Therapy in the ZSF1 Obese Rat Model of Metabolic Syndrome and Heart Failure With Preserved Ejection Fraction

Although decreased protein kinase G (PKG) activity was proposed as potential therapeutic target in heart failure with preserved ejection fraction (HFpEF), randomized clinical trials (RCTs) with type-5 phosphodiesterase inhibitors (PDE5i) showed neutral results. Whether specific subgroups of HFpEF patients may benefit from PDE5i remains to be defined. Our aim was to test chronic sildenafil therapy in the young male ZSF1 obese rat model of HFpEF with severe hypertension and metabolic syndrome. Sixteen-week-old ZSF1 obese rats were randomly assigned to receive sildenafil 100 mg·Kg^-1·d^-1 dissolved in drinking water (ZSF1 Ob SIL, n = 8), or placebo (ZSF1 Ob PL, n = 8). A group of Wistar-Kyoto rats served as control (WKY, n = 8). Four weeks later animals underwent effort tests, glucose metabolism studies, hemodynamic evaluation, and samples were collected for aortic ring preparation, left ventricular (LV) myocardial adenosine triphosphate (ATP) quantification, immunoblotting and histology. ZSF1 Ob PL rats showed systemic hypertension, aortic stiffening, impaired LV relaxation and increased LV stiffness, with preserved ejection fraction and cardiac index. Their endurance capacity was decreased as assessed by maximum workload and peak oxygen consumption (V˙O₂) and respiratory quotient were increased, denoting more reliance on anaerobic metabolism. Additionally, ATP levels were decreased. Chronic sildenafil treatment attenuated hypertension and decreased LV stiffness, modestly enhancing effort tolerance with a concomitant increase in peak, ATP levels and VASP phosphorylation. Chronic sildenafil therapy in this model of HFpEF of the young male with extensive and poorly controlled comorbidities has beneficial cardiovascular effects which support RCTs in HFpEF patient subgroups with similar features.

Phosphodiesterase-5 inhibitor and rat lung ischemia-reperfusion injury

To explore the protective effect of the phosphodiesterase-5 inhibitor, sildenafil, on lung ischemia-reperfusion injury, 30 rats were randomly divided into 3 groups of 10: a sham-operated group A, a lung ischemia-reperfusion injury group B, and a sildenafil preconditioned group C. A 0.1% sildenafil solution was administrated orally 2 h before establishing an in-vivo lung ischemia-reperfusion model in group C; 0.9% normal saline solution was used in the controls. The lung wet-to-dry ratio, malondialdehyde content, myeloperoxidase and nitric oxide synthase activity in groups B and C were significant higher than those in group A, while the partial pressure of oxygen in arterial blood and cyclic guanosine-3',5'-monophosphate content in groups B and C were significant lower than those in group A. Compared to group B, lung wet/dry ratio, malondialdehyde content, myeloperoxidase and nitric oxide synthase activity in group C were significantly lower, while arterial O(2) and cyclic guanosine-3',5'-monophosphate content in group C were significantly higher. The expected histological and cytological changes were significantly alleviated in group C. Oral preconditioning with sildenafil prevented rat lung ischemia-reperfusion injury and improved pulmonary function. The mechanisms of this effect might be prevention of cyclic guanosine monophosphate degradation and inhibition of nitric oxide synthase activity.

Animal models of myocardial and vascular injury

Over the past century, numerous animal models have been developed in an attempt to understand myocardial and vascular injury. However, the successful translation of results observed in animals to human therapy remains low. To understand this problem, we present several animal models of cardiac and vascular injury that are of particular relevance to the cardiac or vascular surgeon. We also explore the potential clinical implications and limitations of each model with respect to the human disease state. Our results underscore the concept that animal research requires an in-depth understanding of the model, animal physiology, and the potential confounding factors. Future outcome analyses with standardized animal models may improve translation of animal research from the bench to the bedside.