Endocrine Abstracts

Background. The endothelial dysfunction prevalent in hypertension and diabetes is associated with an imbalance in the levels of nitric oxide (NO) and superoxide (SO). NAD(P)H oxidase is the predominant source of SO in the vasculature. Objectives. To manipulate levels of SO using the NAD(P)H oxidase inhibitors, apocynin, phenyl arsine oxide (PAO) and 4(2aminoethyl)benzenesulfonyl fluoride (AEBSF) and relate this to NO bioavailability. Methods. NO bioavailability was compared in carotid arteries from SHRSP and WKY and in human internal mammary artery, in the presence and absence of inhibitors. NO bioavailability was measured as the difference in contraction of carotid artery rings to phenylephrine in the absence and presence of NG-nitro-L-arginine-methyl ester and expressed as AUC (g/g). Lucigenin chemiluminescence was used to measure SO levels. Results. In SHRSP NADH stimulated SO production was inhibited by 55±8% by apocynin 1mM, by 38±10% by AEBSF 50mM and by 30±5% by PAO 0.01mM. In organ bath studies PAO and AEBSF attenuated both contractile and relaxant responses at up to 100 times higher concentrations. In contrast apocynin (0.03-3mM) improved NO bioavailability in a concentration dependent manner (from 1.14±0.14 to 3.03±0.19 at 0.3mM, n=6, p=0.001, 95% CI -2.41, -1.36). In WKY 1mM apocynin attenuated NADH stimulated SO production by 37±5% and increased NO bioavailability at concentrations (0.3-3mM) (from 1.60 to 3.21 (g/g) at 0.3mM n=6 p=0.019, 95%CI -2.81, -0.40). Apocynin also attenuated SO production in IMA (from 0.78 to 0.37 nmoles/mg/min at 0.1mM, n=6, p=0.02) and caused vasorelaxation in rings preconstricted with phenylephrine by 19±2% and 40±5% at 0.1 and 0.3mM, n=15, p<0.0001

Conclusions. Systematic investigation of proposed NAD(P)H oxidase inhibitors showed that apocynin has potential therapeutic applications in the vasculature. PAO and AESFB, whilst having inhibitory effects in vitro are limited in their applications due to toxicity. Sensitivity to apocynin was greater in SHRSP, which have increased SO and endothelial dysfunction, relative to WKY.