Fig. 4

Neural inhibition of arterial vasoconstriction. a Phenoxybenzamine (PBZ) completely blocked constriction induced by phenylephrine (PE, p < 0.01), slightly inhibited constriction induced by potassium chloride (KCl, p = 0.02), and significantly decreased constriction induced by 20 V stimulation (*p < 0.01, F(11,58) = 98.75; one-way ANOVA and Tukey-Kramer multi-comparison test). b Guanethidine had no effect on vasoconstriction induced by PE or by KCl, but it blocked the 20 V-induced constriction (*p < 0.01). c PBZ did not inhibit constriction induced by 150 V stimulation, demonstrating that vasoconstriction by high-voltage bypassed the adrenergic neural pathway. d On average, guanethidine failed to block constriction induced by 150 V stimuli. However, the onset of constriction was slowed down (*p < 0.01; one-way ANOVA, F(1,9) = 25.14). Unless specified, significance was determined using one-way ANOVA and Tukey-Kramer multi-comparison test, F(11,58) = 98.75; N = 5 for guanethidine, N = 6 for PBZ and N = 7 control. Horizontal lines indicate the maximum constriction achieved with phenylephrine (green) and potassium chloride (black)