Substance P in Circulating Blood: Origin and Elimination
Substance P (SP) in plasma of fasted cats was found to be 69.3±9.8 fmol/ml (SEM, n = 25, radioimmunassay of extracted plasma). Evisceration lowered the concentration to 28.7±9.0% (n = 5, p < 0.01) after 15 min and to 24.7±9.9% (n = 4, p < 0.01) after 60 min. Ligation of all intestinal arteries and the portal vein reduced the concentration to 55.4±14.1% (n = 7, p < 0.05). No difference between the concentration of SP in portal plasma and in plasma of the V. cava inferior was found (71.8±11.2 versus 68.3±12.1 fmol/ml, n = 6). These results suggest, that the origin of circulating SP is mainly the intestine.