Cellular basis of endothelial dysfunction in small mesenteric arteries from spontaneously diabetic (db/db−/−) mice: role of decreased tetrahydrobiopterin bioavailability

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Abstract
Endothelium‐dependent and ‐independent regulation of vascular tone in small mesenteric arteries (SMA) from control (db/db +/?) and diabetic (db/db −/−) mice was compared. Phenylephrine‐induced maximum contraction, but not sensitivity, of SMA in db/db −/− compared to db/db +/? was enhanced. Acetylcholine (ACh), but not sodium nitroprusside (SNP), ‐induced relaxation was reduced in SMA from db/db −/− compared to db/db +/?. ACh‐induced relaxation of SMA was inhibited by a combination of Nω‐nitro‐L‐arginine and indomethacin in db/db +/?, but not in db/db −/−. Acute incubation of SMA with tetrahydrobiopterin (BH4, 10 μM) and sepiapterin (100 μM) enhanced ACh‐induced relaxation in SMA from db/db −/−, but not from db/db +/? 2,4‐diamino‐6‐hydroxypyrimidine, an inhibitor of GTP cyclohydrolase I, (10 mM), impaired the sensitivity of SMA from db/db +/? to ACh, which was restored by co‐incubation with BH4 (10 μM). BH4 and superoxide dismutase (SOD, 150 u ml−1), either alone or in combination, had no effect on either ACh or SNP‐induced relaxation in SMA from eNOS −/− mice. Incubation of SMA with SOD (150 iu ml−1), catalase (200 iu ml−1) and L‐arginine (1 mM) had no effect on ACh‐induced relaxation of SMA. However, the combination of polyethylene glycol‐SOD (200 iu ml−1) and catalase (80 u ml−1) improved the sensitivity of ACh‐induced relaxation in db/db −/−, but not in db/db +/?. These data suggest that increased production of superoxide anions and decreased availability of BH4 result in an ‘uncoupling’ of nitric oxide synthase and endothelial dysfunction in SMA from db/db −/− mice. British Journal of Pharmacology (2002) 136, 255–263; doi:10.1038/sj.bjp.0704683