Substance P potentiates the algogenic effects of intraarterial infusion of adenosine.

Objectives: This study investigated whether substance P potentiates the muscular and cardiac pain caused by the intraarterial infusion of adenosine, an autocoid known to induce muscular and cardiac ischemic-like pain in humans.
Background: Substance P is involved in the generation of neurogenic inflammation and causes cutaneous hyperalgesia. Because substance P is present in perivascular nerves it might also cause muscular and cardiac hyperalgesia. To test this hypothesis its effects on adenosine-induced muscular and cardiac pain were investigated in humans.
Methods: A randomized, crossover study of the algogenic effects of the intrailiac infusion of increasing scalar doses (from 125 to 2,000 micrograms/min) of adenosine or substance P (11.2 pmol/min) for 3 min, followed by the simultaneous infusion of substance P plus the same doses of adenosine, was carried out in nine patients with no evidence of peripheral vascular disease. A similar protocol was carried out by infusing increasing scalar doses of adenosine (from 50 to 800 micrograms/min) or substance P (11.2 pmol/min) for 3 min, followed by the simultaneous infusion of substance P plus the same doses of adenosine, into the left coronary artery of eight patients with angina. Pain severity, assessed by a visual analog scale, is presented as median. The remaining data are presented as mean value +/- 1 SD.
Results: All patients experienced pain during both adenosine and substance P plus adenosine infusion; no patient experienced pain during the infusion of substance P alone. During intrailiac infusion, all patients experienced pain in the right leg that occurred earlier (207 +/- 152 vs. 321 +/- 154 s, p < 0.05) and was greater (47 vs. 30 mm, p < 0.05) during the simultaneous infusion of substance P plus adenosine than during the infusion of adenosine. Similarly, during intracoronary infusion, all patients experienced chest pain that occurred earlier (409 +/- 242 vs. 596 +/- 210 s, p < 0.05) and was greater (51 vs. 33 mm, p < 0.05) during the simultaneous infusion of substance P plus adenosine than during infusion of adenosine. No patient exhibited electrocardiographic signs of ischemia.
Conclusions: Substance P does not cause muscular or cardiac pain, but it provokes muscular and cardiac hyperalgesia.