Regulation of blood pressure by L-arginine-nitric oxide pathway within the superior colliculus of rats.

Injection into the superior colliculus of anaesthetised rats of the nitric oxide (NO) synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME; 1 micromol), but not its inactive enantiomer N(omega)-nitro-D-arginine methyl ester (D-NAME; 1 micromol), significantly (P < 0.01) increased the mean arterial blood pressure. Injection to the superior colliculus of L-arginine (L-Arg; 1 micromol), the substrate for NO synthase, significantly (P < 0.01) lessened the pressor effect of L-NAME, while D-arginine (D-Arg; 1 micromol) did not affect it. L-Arg (7.5 micromol), but not D-Arg (7.5 micromol) administered at the peak of the pressor response to L-NAME (1 micromol) also partially reversed this pressor response (P < 0.05). These data would suggest that endogenously produced NO acts within the superior colliculus to modulate the arterial blood pressure.