In Situ Inhibition of Uterine Activity by Indomethacin: Possible Relevance to Preterm Labor Prevention After Fetal Surgery By Jennifer Garza, Nicholas Clayton, Amir Kaviani, Timothy J. Maher, and Dario Fauza Boston, Massachusetts Purpose: This report is an analysis of the effects of local indomethacin delivery on uterine activity in vitro. Methods: Isolated strips of time-dated pregnant rats’ myo- metrium were placed within controlled tissue baths. Sponta- neous muscular activity was recorded by a force transducer connected to a polygraph at cumulative concentrations of indomethacin. Statistical analysis was by single-factor anal- ysis of variance (ANOVA), with P values of less than .05 considered significant. Results: Within a narrow concentration range, the effects of indomethacin on frequency and amplitude of myometrial contractions were nonmonotonic, with an increase in fre- quency at levels that began to depress amplitude. However, both amplitude and frequency were significantly depressed and eventually totally abolished at most concentrations stud- ied (P  .05). Conclusions: Indomethacin administered in situ consistently inhibits or completely arrests overall myometrial activity. The concept of local myometrial delivery of indomethacin, possibly via slow release systems, may prove clinically use- ful as an adjuvant to its systemic administration in preterm labor prevention after fetal surgery, warranting further trials in vivo. J Pediatr Surg 39:1173-1175. © 2004 Elsevier Inc. All rights reserved. INDEX WORDS: Premature labor, fetal surgery, uterus, myo- metrium, indomethacin. P RETERM LABOR remains the foremost complica- tion of fetal surgery as well as the overall leading cause of fetal and neonatal mortality. Current tocolysis regimens include assorted drugs delivered systemically, but have met with limited success, particularly after surgical fetal intervention. We have previously shown that a local strategy, namely a prolonged excitatory blockade of the myometrium by intramural administra- tion of a suspension of biodegradable microspheres loaded with a local anesthetic, prevented premature de- livery in a leporine model of fetal surgery. 1 Further analysis in vitro showed that local anesthetics prevent myometrial membrane depolarization in a dose-depen- dent mode to the point of completely arresting uterine contraction. 2 In other experiments, local delivery of bot- ulinus toxin has also been shown to consistently inhibit, or completely arrest, myometrial activity in a potentially reversible fashion. 3 The current study was aimed at determining whether a different class of drugs, namely cyclooxygenase inhibitors, could also inhibit pregnant uterine activity in vitro as a prerequisite for its potential application via slow release local drug delivery systems. MATERIALS AND METHODS The Harvard Medical School (HMS) animal management program is sanctioned by the American Association for the Accreditation of Laboratory Animal Care (AAALAC-file # 000009) and meets National Institutes of Health standards as set forth in the Guide for the Care and Use of Laboratory Animals (National Research Council Publication, Revised 1996). The current study was approved by the HMS Standing Committee on Animals, under protocol # 03353. Time-dated pregnant Wistar rats (Charles River Laboratories, Wil- mington, MA) on gestational day 14 (term, 21 to 23 days) were killed by intraperitoneal injection of 100 mg/kg of pentobarbital (Abbott, North Chicago, IL). Four strips of myometrium of approximately 1 cm in length and 3 to 4 mm wide (approximately 0.5 mL in volume) were obtained from both uterine horns (2 from each) per animal and dissected free from gestational membranes. The uterine samples were then placed within 10-mL tissue baths containing DeJalon’s solution modified as previously described 4 at 32°C and continuously exposed to a 95% O 2 , 5% CO 2 sweep gas, under a resting tension of 1 g. Spontaneous muscular activity was recorded by a Grass FT03 force transducer (Grass Corp, Quincy, MA) connected to a Grass Model 7 polygraph, calibrated as per manufacturer’s instructions. Myometrial samples were allowed to equilibrate for at least 30 minutes, after which time, predictable, stable activity could be observed. Samples that did not maintain regular phasic activity after this period were discarded (5 of 38 uterine samples were discarded for failing to meet this criterion). Once baseline values for amplitude and frequency of contractions were recorded, cumulative concentrations of indomethacin (Astra USA, Inc, Westbotough, MA), between 1  10 -9 and 1  10 -3 mol/L, in pH-balanced saline, were added to the tissue baths. Myometrial activity data-points for each drug concentration were entered as mean percen- tual variations from the baseline values for both amplitude and fre- quency of contractions. After data collection for each sample was complete, the tissue bath was completely washed out of the drug, and From the Departments of Surgery, Children’s Hospital and Harvard Medical School; Massachusetts College of Pharmacy and Health Sciences; and Harvard Center for Minimally Invasive Surgery, Boston, MA. Address reprint requests to Dario O. Fauza, MD, Children’s Hos- pital, 300 Longwood Ave, Fegan 3, Boston, MA 02115. © 2004 Elsevier Inc. All rights reserved. 0022-3468/04/3908-0002$30.00/0 doi:10.1016/j.jpedsurg.2004.04.006 1173 Journal of Pediatric Surgery, Vol 39, No 8 (August), 2004: pp 1173-1175