Fig. 2. Increase in tissue cyclic guanosine monophosphate (cGMP) concentrations (picomole per milligram of tissue) in arterial segments of the Circle of Willis and extracranial portion of internal carotid artery after10-min incubation in increasing concentrations of sodium nitroprusside (SNP). Error bars represent SE. *Significant differences between intracranial and extracranial arteries. #Significant difference from 0, and 10−9m SNP concentrations. @Significant difference from 10−7m SNP concentration.