Neonates with congenital diaphragmatic hernia (CDH) suffer from a diaphragmatic defect, lung hypoplasia, and pulmonary hypertension, with poor lung function forming the major clinical challenge. Despite prenatal diagnosis and advanced postnatal treatment strategies, the mortality rate of CDH is still high. CDH has been subject of extensive research over the past decades, but its etiology remains unknown. A major problem with CDH is the failure to predict the individual response to treatment modalities like high-frequency ventilation, inhaled nitric oxide, and extracorporeal membrane oxygenation. In this study, we tested the possibility that CDH lungs are surfactant protein deficient, which could explain the respiratory failure and difficulties in treating CDH infants. We investigated this hypothesis in the nitrofeninduced CDH rat model and assessed the cellular concentrations of surfactant protein (SP)-A, -B, and -C mRNA with a quantitative radioactive in situ hybridization technique. No differences were observed between control and CDH lungs for SP mRNA expression patterns. The cellular concentration (mean OD) of SP-A and SP-B mRNA was similar at all stages whereas the mean OD of SP-C mRNA and the volume fraction of cells (% Area) expressing SP mRNA was higher in CDH lungs at term. Immunohistochemical analysis revealed no differences between control and CDH lungs for SP protein expression. No differences in the mean OD or % Area for the SP mRNAs were found between the ipsi-and contralateral side of CDH lungs. We conclude that there is no primary deficiency of surfactant proteins in the nitrofen-induced CDH rat model. CDH is an anomaly occurring 1 in 3000 live births (1). It is characterized by a diaphragmatic defect, severe lung hypoplasia, and pulmonary hypertension, and in 40% of the patients other severe birth defects such as cardiac abnormalities are present (2, 3). Despite years of extensive research, the etiology of CDH remains unknown (4). Clinically, pulmonary hypoplasia and pulmonary hypertension form the major problems in CDH (5).Many CDH studies have focused on treatment modalities such as conventional ventilation with gentle handling of the fragile lung, high-frequency ventilation, ECMO, in utero tracheal ligation with or without betamethasone injection, inhaled nitric oxide, and prenatal injections of betamethasone, TSHreleasing hormone, or a combination of both hormones. Although selected centers have reported improved survival (6, 7), the overall mortality rate, however, is still variably high, so that CDH continues to be a serious problem in the neonatal and pediatric surgical intensive care unit, with optimal treatment for CDH still the subject of ongoing debate (5, 8 -10

1 We previously reported activation of an inhibitory adrenergic and a non-adrenergic noncholinergic (NANC) pathway during abdominal surgery relaxing the rat gastric fundus. In the present study, we investigated the possible role of nitric oxide (NO) and vasoactive intestinal polypeptide (VIP) in the NANC part of the surgery-induced fundic relaxation. 3 Guanethidine partly reduced the manipulation-induced fundic relaxation. Addition of L-NOARG reduced this non-adrenergic component, whereas the non-selective VIP receptor antagonist had no signi®cant e ect. Combination of L-NOARG and the non-selective VIP antagonist however further reduced the relaxation to manipulation. 4 The selective VIP 1 receptor antagonist reduced the mean and maximal relaxation induced by abdominal surgery in the presence of guanethidine. When combined with L-NOARG, the relaxation of the gastric fundus was almost completely abolished. The VIP 1 receptor antagonist alone had no signi®cant e ect on the mean and maximal relaxation, but enhanced recovery of fundic tone. 5 In conclusion, as VIP 1 receptors are not present in the rat gastric fundus, these results suggest that the NANC inhibitory pathway activated during abdominal surgery involves VIP 1 receptors, most likely in the a erent limb. The inhibitory neurotransmitters released at the level of the gastric fundus smooth muscle are NO and a substance di erent from VIP.

1 Guanethidine is commonly used as a drug to investigate adrenergic neurotransmission and, in combination with atropine, to realize non-adrenergic non-cholinergic (NANC) conditions. Previous studies suggested a nicotinic acetylcholine receptor blocking e ect of guanethidine. Therefore, we investigated the e ect of increasing concentrations of guanethidine (0.1 ± 100 mM) on nicotineinduced relaxations of longitudinal muscle strips of rat gastric fundus. 2 In the presence of 1 mM atropine and 3 mM guanethidine, nicotine (30 mM) induces a fast and sustained relaxation which is partly inhibited by the nitric oxide synthase inhibitors No-nitro-Larginine (L-NOARG) and No-nitro-L-arginine methyl ester (L-NAME) (both 30 and 100 mM). One mM tetrodotoxin (TTX) completely blocks this nicotine-induced relaxation. 3 High concentrations of guanethidine (510 mM), but not adrenoceptor blockade by the aadrenoceptor antagonist phentolamine in combination with the b-adrenoceptor antagonist nadolol (both 3 mM), inhibit the nicotine-induced relaxation. 4 Guanethidine (0.1 ± 100 mM) has no e ect on relaxations induced by electrical ®eld stimulation (EFS; 1 ± 8 Hz), nitric oxide (NO; 0.01 ± 1 mM), vasoactive intestinal polypeptide (VIP; 0.1 ± 10 nM) or isoprenaline (1 ± 10 nM). 5 We conclude that high concentrations of guanethidine (510 mM) block nicotine-induced NANC relaxations of longitudinal muscle strips of the rat gastric fundus most likely at the level of the nicotinic acetylcholine receptor.

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