A MODEL OF INTRAUTERINE INFECTION AND PRETERM DELIVERY IN MICE

OBJECTIVE: Our purpose was to determine whether intrauterine bacterial inoculation leads to preterm delivery in mice. STUDY DESIGN: Fifty-fo ur female CD-1 mice at 75% of the length of the gestational period (14 .5 days) received either an intrauterine bacterial inoculum of 2 to 10 x 10(3) Escherichia coli (n = 33), an intraperitoneal bacterial inocu lum (n = 7), or an intrauterine injection of a sterile solution (n = 1 4). RESULTS: Delivery within 48 hours of surgery occurred in 91% of mi ce after intrauterine bacteria, in 0% after intraperitoneal bacteria, and in 7% after sterile intrauterine injection (p < 0.001). Intrauteri ne bacterial inoculation produced systemic infection (i.e., recovery o f organisms from culture of the heart) in 50% of animals post partum. Intraperitoneal bacteria and intrauterine saline solution injections r esulted in systemic infection rates of 20% and 0%, respectively, 48 ho urs after surgery. Five of seven animals injected with bacteria into t he uterus had histologic evidence of metritis, mild in all cases. Intr auterine bacterial inoculation resulted in induction of ribonucleic ac id transcripts for tumor necrosis factor-alpha, interleukin-1 alpha, i nterleukin-1 beta, and cyclooxygenase-2. CONCLUSIONS: Intrauterine ino culation with Escherichia coli in mice leads to preterm delivery and t he local induction of factors known to be involved in human preterm la bor with infection. The observation that intraperitoneal bacterial ino culation does not result in preterm delivery suggests that in this mod el labor is the product of a local (uterine) stimulus.