Plasma and saliva substance P levels: the effects of acute pain in pregnant and non-pregnant women.

Substance P like immunoreactivity (SPLI) and total protein (TP) concentrations in plasma and saliva were measured in 80 healthy female patients divided into the following four groups: women in group 1 were not pregnant and they were awaiting tubal ligation; women in group 2 were not pregnant but they experienced acute postoperative pain following hysterectomy; women in group 3 were pregnant and were awaiting elective cesarean section; and women in group 4 were in active labor and experienced acute labor pain. Pain intensity was assessed using verbal Likert pain scores. The absolute measured concentration of SPLI (SPLIabs) was divided by the TP concentration to obtain corrected SPLI (SPLIcorr) concentration. Results were expressed mean +/- 1 SE and analyzed using analysis of variance with 95% confidence (P < 0.05). SPLIcorr concentrations were 1.8 +/- 0.1, 1.8 +/- 0.2, 1.1 +/- 0.1 1.1 +/- 0.1 pg/mg protein in groups 1, 2, 3 and 4, respectively. Patients in both pregnant groups had significantly lower plasma SPLIcorr concentrations compared to the non-pregnant groups. However, the presence of acute postoperative pain or labor pain did not significantly alter plasma SPLIcorr concentrations. Saliva SPLI concentrations were not significantly different among the four groups.