Figure 4. Control experiments.

A, in three ‘freely perfused’ rats, we infused tiron into the superficial epigastric artery while acutely restricting blood flow through the iliac artery and vein to trap tiron in the hindlimb circulation; note that tiron still had no effect on the pressor response. B, infusion of tiron into the jugular vein (IV) in six, ‘ligated’ rats slightly and insignificantly reduced the pressor response to contraction (P = 0.32). C, in another six, ‘ligated’ rats, acutely restricting blood flow through the iliac artery and vein while infusing tiron i.v. mitigated (P = 0.97) the effect seen in (B). D, i.v. tiron infusion did not change the pressor response to electrical stimulation of the tibial nerve at 10–20 times the muscle twitch threshold in five ‘ligated’ rats that underwent neuromuscular blockade (P = 0.93).