Lamellar Body Counts in Fetal Rabbits' Experimental Diaphragmatic Hernia and Tracheal Ligation

Experimental tracheal ligation (TL) has been shown to reverse the pulmonary hypoplasia associated with congenital diaphragmatic hernia (CDH) and to normalize gas exchange. The purpose of this study was to determine whether the TL would correct the surfactant deficiency present in the fetal rabbit model of CDH by using lamellar body count. Lamellar bodies are synthesized and secreted by the type II pneumocytes of fetal lung. The phospholipids present in these bodies constitute the major component of pulmonary surfactant. Twenty-one pregnant New Zealand rabbits underwent hysterotomy and fetal surgery on gestational day 24. Two fetuses of each pregnant rabbit were operated. In the fetus of one end of bicornuate uterus, left DH was created by excision of fetal diaphragm through open thoracotomy (DH Group). In the fetus of the other end of bicornuate uterus, left DH and TL were created (TL Group). The fetuses were delivered by Cesarean section on gestational day 31. Fourteen in control group, 12 in the DH group and 13 in TL group were born alive. En bloc excision of lungs, bronchi and trachea was done in all newborn rabbits. A five Fr catheter was inserted through trachea and repeated irrigations with 10 cc normal saline were done. The irrigated fluid was centrifuged at 280 xg for 5 minutes and the lamellar bodies were counted with the upper level fluid in platelet channel of electronic cell counter. The average lamellar body counts were 37.1 +/- 14.2 x 10(3)/microL in control group, 11.5 +/- 4.4 x 10(3)/microL in DH group, and 6.5+/- 0.9 x 10(3)/microL in TL group. Lamellar body count in DH group was lower than in control group and did not increase after TL. This study shows TL has no therapeutic effect on decreased surfactant level of CDH and the pregnant rabbit is appropriate for the animal model of CDH.

Experimental Diaphragmatic Hernia and Tracheal Ligation in a Fetal Rabbit Model

Despite of advances in perinatal management and treatment modalities, congenital diaphragmatic hernia (CDH) remains a frustrating problem. Although the sheep has been the most reliable experimental animal of fetal surgery in CDH, the rabbits has some possible advantages over sheep; lower cost, smaller body size, year-round availability, high number of fetuses per pregnancy, and short gestational period. The purpose of this study is to evaluate the feasibility of the animal model of CDH in rabbits. Twenty seven pregnant New Zealand rabbits underwent hysterotomy and fetal operation on gestational day 24 or 25. Two fetuses of each pregnant rabbit were operated. In the fetus of one end of bicornuate uterus, left diaphragmatic hernia was created by excision of fetal diaphragm through open thoracotomy (DH Group). In the fetus of the other end of bicornuate uterus, left diaphragmatic hernia was created and tracheal ligation by small-sized Surgiclip(R) (USSC, Norwalk, Conn., USA) was performed through cervical incision (TL Group). Among twenty seven pregnant rabbits, twelve were born alive with diaphragmatic hernia and eight were born alive with diaphragmatic hernia & tracheal ligation. The most commonly herniated abdominal organ was the left lobe of liver. In DH group, the lungs were hypoplastic with a decrease in lung weight/body weight ratio, a reduction in number of alveoli, an increase of vascular medial wall thickness of pulmonary arteries. The alveoli were immature with thick alveolar septum and increased interstitium. In TL group, the alveoli were more mature than that of DH group and no significant difference from control group was existed. Thus this study demonstrates that (1)Diaphragmatic hernia can be created in rabbits by fetal surgery, (2)Tracheal ligation can be performed in rabbits by fetal surgery, (3)Experimental diaphragmatic hernia results in pulmonary hypoplasia, (4)Concurrent tracheal ligation prevents pulmonary hypoplasia that resulted from diaphragmatic hernia. The above mentioned results show that pregnant New Zealand rabbit is appropriate as the animal model of CDH.