Received for publication February 1, 2008.
Revised April 30, 2008.
Accepted for publication May 1, 2008.

Sustained Soluble Guanylate Cyclase Stimulation offsets NOS Inhibition to Restore Acute Cardiac Modulation by Sildenafil

Abstract

Phosphodiesterase type 5 (PDE5) inhibitors are used to treat erectile dysfunction, and growing evidence supports potential cardiovascular utility. Their efficacy declines with reduced nitric oxide synthase (NOS) activity common to various diseases. We tested whether direct soluble guanylate cyclase (sGC) stimulation restores in vivo cardiovascular modulation by (PDE5) inhibition despite acute or chronically suppressed NOS activity. Mice (C57/Bl6, n=62) were studied by in vivo pressure-volume analysis to assess acute modulation by PDE5-inhibitor sildenafil (SIL, 100 µg/kg/min) of the cardiac response to isoproterenol (ISO) with or without NOS inhibition (L-NAME) and co-treatment by the sGC stimulator BAY 41-8543. SIL induced mild vasodilation but no basal cardiac effects and markedly blunted ISO stimulated contractility. Acute BAY 41-8543 at a dose lacking cardiovascular effects did not alter ISO responses. However, after acute L-NAME, SIL ceased to influence cardiovascular function, but adding BAY 41-8543 fully restored SIL effects. After 1-wk L-NAME, neither SIL nor SIL+BAY 41-8543 acutely induced vasodilation or blunted ISO responses. However, sustained BAY 41-8543 despite concurrent NOS inhibition restored the cardiovascular efficacy of SIL. The disparity between acute and chronic NOS inhibition related to diffusion of PDE5 away from myocyte Z-bands coupled with reduced protein kinase G activation. Both were restored by sustained sGC co-stimulation. Thus, PDE5 regulation of adrenergic reserve and systemic vasodilation depends upon NOS-induced cGMP/PKG, and can be enhanced by sustained low-level stimulation of sGC. This may prove beneficial for enhancing the efficacy of PDE5 inhibitors in conditions with chronically reduced NOS activity.

Key words: beta-adrenergic, contractility, cyclic GMP, myocyte, nitric oxide synthase, phosphodiesterase type 5