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

1 Endothelium-dependent and -independent regulation of vascular tone in small mesenteric arteries (SMA) from control (db/db +/?) and diabetic (db/db -/-) mice was compared. 2 Phenylephrine-induced maximum contraction, but not sensitivity, of SMA in db/db compared to db/db +/? was enhanced. 3 Acetylcholine (ACh), but not sodium nitroprusside (SNP), -induced relaxation was reduced in SMA from db/db -/- compared to db/db +/?. 4 ACh-induced relaxation of SMA was inhibited by a combination of N-omega-nitro-L-arginine and indomethacin in db/db +/?, but not in db/db -/-. 5 Acute incubation of SMA with tetrahydrobiopterin (BH4, 10 muM) and sepiapterin (100 muM) enhanced ACh-induced relaxation in SMA from db/db -/-, but not from db/db +/? 2,4-diamino-6-hydroxypyrimidine, an inhibitor of GTP cyclohydrolase 1, (10 mm), impaired the sensitivity of SMA from db/db +/? to ACh, which was restored by co-incubation with BH4 (10 muM) 6 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. 7 Incubation of SMA with SOD (150 iu ml(-1)), catalase (200 in 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 +/?. 8 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.