Peuler JD, Phelps LE. Sildenafil does not enhance but rather attenuates vasorelaxant effects of antidiabetic agents.
J Smooth Muscle Res 2015;
51:22-36. [PMID:
26004378 PMCID:
PMC5137313 DOI:
10.1540/jsmr.51.22]
[Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Type 2 diabetic men commonly experience erectile dysfunction for which
phosphodiesterase-5 (PDE5) inhibitors like sildenafil (Viagra) are often recommended. By
preventing degradation of cyclic guanosine monophosphate (cGMP) in vascular smooth muscle,
these inhibitors also enhance arterial vasorelaxant effects of nitric oxide donors (which
stimulate cGMP synthesis). In the present work, we confirmed this enhancing effect after
co-administration of sildenafil with nitroprusside to freshly-isolated rat tail arterial
tissues. However, in the same tissues we also observed that sildenafil does not enhance
but rather attenuates vasorelaxant effects of three commonly-used antidiabetic drugs, i.e.
the biguanide metformin and the thiazolidinediones pioglitazone and rosiglitazone. Indeed,
sildenafil completely blocked vasorelaxant effects of low concentrations of these drugs.
In addition, we found that this same novel anti-vasorelaxant interaction of sildenafil
with these agents was abolished by either 1) omitting extracellular glucose or 2)
inhibiting specific smooth muscle glycolytic pathways; pathways known to preferentially
utilize extracellular glucose to fuel certain adenosine triphosphate (ATP)-dependent ion
transporters: e.g. ATP-sensitive K channels, sarcoplasmic reticulum Ca-ATPase, plasma
membrane Ca-ATPase and Na/K-ATPase. Accordingly, we suspect that altered activity of one
or more of these ion transporters mediates the observed attenuating (anti-vasorelaxant)
interaction of sildenafil with the antidiabetic drugs. The present results are relevant
because hypertension is so common and difficult to control in Type 2 diabetes. The present
data suggest that sildenafil might interfere with the known antihypertensive potential of
metformin and the thiazolidinediones. However, they do not suggest that it will interact
with them to cause life-threatening episodes of severe hypotension, as can occur when it
is co-administered with nitrates.
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