Fig. 6. Vasodilator responses to an increase in levels of carbon dioxide (Pco2= 50 mmHg) (A ) or acetylcholine (10−6, 10−5, and 10−4m) (B ) in the absence or presence of NG-nitro-l-arginine methyl ester (L-NAME; 10−4m) in rat cerebral parenchymal arterioles. Baseline diameters were 7.3 ± 1.7 and 8.2 ± 1.9 μm for control arterioles and arterioles treated with L-NAME for carbon dioxide-induced vasodilation and 6.5 ± 1.6 and 6.5 ± 1.3 μm for control arterioles and arterioles treated with L-NAME for acetylcholine-induced vasodilation, respectively. Vasoconstrictor responses to prostaglandin F2α(5 × 10−7m) were 15.2 ± 4.8 and 14.1 ± 3.2% for control arterioles and arterioles treated with L-NAME for carbon dioxide-induced vasodilation and 10.9 ± 3.6 and 18.1 ± 11.0% for control arterioles and arterioles treated with L-NAME for acetylcholine-induced vasodilation, respectively. Data are expressed as mean ± SD. * The difference between control arterioles and arterioles treated with L-NAME for acetylcholine-induced vasodilation was statistically significant.