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To measure prostaglandin E2 levels during labor induction with a sustained-release vaginal polymer insert (prostaglandin E2 insert) and to determine whether Bishop score change correlated with tachysystole. Twelve primiparas and 12 multiparas were treated with a 0.3 mg per hour sustained-release polymer vaginal prostaglandin E2 insert for up to 24 hours. Bishop score was assessed at start and end of therapy, and serum samples were collected at 4-hour intervals. Prostaglandin E2 metabolite (PGEM) levels were measured by specific enzyme immunoassay. Exposure averaged 13.5 ± 7.2 hours. Four patients (16.7%, three nulliparas) had tachysystole. Mean PGEM levels increased from 187 ± 42 pg/mL at baseline to 548 ± 110 pg/mL at 12 hours (P < .05) and remained relatively stable thereafter. Nulliparas with Bishop score changes of four points or more had the highest increase, with average peak levels of 985 ± 109 pg/mL, compared with 452 ± 58 pg/mL for all others (P < .001). Patients with tachysystole had higher 4-hour (P < .01) and overall (P < .04) increases in PGEM level. Removal of the insert led to an average decrease of 335 pg/mL in PGEM levels (P < .01). The decrease correlated with the PGEM level measured before removal (r = .94, P < .0001) and the maximum PGEM increase from baseline (r = .94, P < .0001). The mean mixed venous cord PGEM level was 409 ± 375 pg/mL. Administration of the prostaglandin E2 insert led to a sustained increase in circulating PGEM levels in women who had labor induction. Peak PGEM levels correlated with Bishop score improvement. Rapid increases in prostaglandin E2 levels might cause tachysystole.

To assess relative expression levels of mRNA for EP3 isoforms EP3-2, EP3-3, and EP3-6 in human myometrium in various physiologic states.Using semiquantitative reverse transcriptase-polymerase chain reaction, we analyzed myometrial samples from 46 women (ten menopausal, ten nongravid premenopausal, 19 gravidas, seven premenopausal misoprostol-treated nongravid women) for the specific expression of mRNA messages for the EP3 receptor isoforms EP3-2, EP3-3, and EP3-6.We found that the expression of EP3-2 was significantly lower in gravid than nongravid myometrium (P.0001). Levels of the EP3-6 message were higher in gravid samples than in nongravid specimens (P.02). EP3-3 mRNA was present in higher levels in menopausal samples compared with the other groups.The selective fluctuation of mRNA expression of the different EP3 isoforms suggests the possibility of an important regulatory role for these receptors in myometrial contractility. Additional studies are necessary to evaluate the exact mechanism of action of EP3 receptor isoforms in human myometrium.