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CLINICAL RESEARCH

Acute Phosphodiesterase 5 Inhibition Mimics Hemodynamic Effects of B-Type Natriuretic Peptide and Potentiates B-Type Natriuretic Peptide Effects in Failing But Not Normal Canine Heart

Division of Cardiology, Department of Medicine, Johns Hopkins Medical Institutions, Baltimore, Maryland

Manuscript received May 2, 2006; revised manuscript received August 18, 2006, accepted August 30, 2006.

^_* Reprint requests and correspondence: Dr. David A. Kass, Division of Cardiology, Johns Hopkins Medical Institutions, Ross 835, 720 Rutland Avenue, Baltimore, Maryland 21205. (Email: dkass{at}jhmi.edu).

Objectives: The aim of this work was to test whether acute phosphodiesterase 5 (PDE5) inhibition via sildenafil (SIL) mimics and/or potentiates cardiorenal effects of exogenous natriuretic peptide (NP) infusion.

Background: Heart failure (HF) is often accompanied by elevated NP secretion yet blunted responsiveness. Such NP resistance may, in part, relate to increased cyclic guanosine monophosphate (cGMP) catabolism by PDE5.

Methods: Dogs (n = 7) were studied before and after tachypacing-induced HF. Animals received 30-min infusion of B-type natriuretic peptide (BNP) (2 µg/kg bolus, 0.02 µg/kg/min), and on a separate day SIL (1 mg/kg, intravenous), followed by BNP (SIL + BNP). Phosphodiesterase 5 activity was measured in lung, vasculature, and kidney.

Results: At baseline (non-failing), BNP lowered central venous, pulmonary capillary wedge, diastolic, mean pulmonary artery, and mean arterial pressure. Sildenafil had no effects, and SIL + BNP was similar to BNP alone. In contrast, SIL lowered these pressures similarly to BNP in dogs with HF, and SIL + BNP was additive in further reducing pulmonary pressures over BNP alone. Plasma cGMP/plasma BNP ratio was markedly reduced with HF, indicating NP resistance. Sildenafil plus BNP increased this ratio in HF, but had no effect in non-failing animals. Sildenafil had no independent diuretic/natriuretic effects nor did it enhance BNP effects under baseline or HF conditions. In HF, PDE5 activity was significantly increased in the systemic and pulmonary vasculature and in the kidney.

Conclusions: The PDE5 activity in systemic and pulmonary vasculature increases in HF rendering hemodynamic responses to PDE5 inhibition identical to those from BNP infusion. Natriuretic peptide desensitization in HF relates, in part, to increased PDE5 activity, supporting a therapeutic role for PDE5 inhibition.

Abbreviations and Acronyms   ANP = atrial natriuretic peptide   BNP = B-type natriuretic peptide   cGMP = cyclic guanosine monophosphate   dPAP = diastolic pulmonary artery pressure   HF = heart failure   LV = left ventricle/ventricular   LVEF = left ventricular ejection fraction   mPAP = mean pulmonary artery pressure   NP = natriuretic peptide   PDE5 = phosphodiesterase type-5   SIL = sildenafil   SV = stroke volume

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