ObjectiveTo assess the roles of interleukin-1β, interleukin-8, and fibroblasts in the lower uterine segment during parturition.MethodsLower uterine segment biopsy specimens were obtained from 36 women undergoing cesarean delivery at various stages of cervical dilation (less than 2 cm,n= 8; 2 to less than 4 cm,n= 9; 4-6 cm,n= 10; more than 6 cm,n= 9). The concentrations of interleukin-1β and interleukin-8 in protein extracts prepared from the tissue samples were measured by enzyme immunoassays. The effect of incubation with interleukin-1β (30 U/mL) on interleukin-8 secretion by lower uterine segment fibroblasts in vitro also was determined.ResultsThe median interleukin-1β concentration in the specimens increased from 1.3 pg/mg of total protein at less than 2 cm of dilation to 22.2 pg/mg of total protein at 4-6 cm of dilation (P< .05). No further increase was detectable after 6 cm of dilation. The interleukin-8 concentration increased from 17.2 pg/mg of total protein at less than 2 cm of dilation to 2080.7 pg/mg of total protein at 4-6 cm of dilation (P< .05), thus paralleling the increase in interleukin-1β concentration. Interleukin-1β induced a significant increase in interleukin-8 secretion by fibroblasts in vitro, from 0.8 ng/106cells to 35.6 ng/106cells.ConclusionThe increase in interleukin-8 concentration in the lower uterine segment during parturition may be induced by interleukin-1β and fibroblasts may be one of the sources of this interleukin-8.