Kidney development in the nitrofen-induced pulmonary hypoplasia and congenital diaphragmatic hernia in rats

The relationship of the developing lung and kidney is not completely understood. Renal enlargement has been reported in association with pulmonary hypoplasia in congenital diaphragmatic hernia (CDH). Recent studies suggest that retinoids may be involved in the pathogenesis of CDH. The aims of this study were to investigate the effects of pulmonary hypoplasia on renal development and to evaluate retinoids status of kidneys in the nitrofen model of CDH.

Pregnant rats were exposed to either olive oil or 100 mg of nitrofen on day 9.5 of gestation. Fetuses were recovered at term and divided into 3 groups: 1, control (n = 69); 2, nitrofen without CDH (n = 25); and 3, nitrofen with CDH (n = 40). Kidneys were dissected, weighed, and processed for biochemical measurements of DNA, proteins, total retinol content, and for immunohistochemical staining of proliferating cells.

Kidneys were smaller in nitrofen-exposed animals vs control animals (group 3, 0.65 +/- 0.08; group 2, 0.62 +/- 0.09 vs group 1, 0.73 +/- 0.09% of body weight, P < .001), and there were no differences between right and left kidney weight in all the 3 groups. Regression of total kidney weight on body weight showed a linear direct correlation between them in all the groups. Total amount of DNA was significantly reduced in nitrofen-exposed animals vs controls (group 3, 80.58 +/- 35.65; group 2, 64.71 +/- 20.28 vs group 1, 110.34 +/- 42.15 microg, P < .01), but the DNA concentration remained the same in the 3 groups (group 3, 3.59 +/- 1.26; group 2, 3.06 +/- 1.19; group 1, 3.43 +/- 1.05 microg DNA/mg kidney). Total protein content (group 3, 1145.59 +/- 500.36; group 2, 993.2 +/- 276.62; group 1, 1287.48 +/- 312.52 microg), protein concentration (group 3, 49.76 +/- 11.12; group 2, 43.95 +/- 6.79; group 1, 47.38 +/- 6.93 microg protein/mg kidney), and protein-to-DNA ratio (group 3, 15.12 +/- 5.98; group 2, 16.22 +/- 6.85; group I, 16.16 +/- 7.02 microg/microg) were similar in all groups. Retinol concentration was significantly reduced in both nitrofen-exposed groups compared with the control group (group 3, 1.35 +/- 0.24; group 2, 1.28 +/- 0.11; group 1, 2.53+/-0.61 microg retinol/g kidney). Proliferation index was similar in all 3 groups (group 3, 50.43 +/- 8.81; group 2, 47.96 +/- 6.01; group 1, 47.64 +/- 5.76% of proliferating cells).

Our data clearly show that renal enlargement in association with pulmonary hypoplasia is not seen in the nitrofen-induced CDH. These results rule out any possible relationship between lung and kidney development. Moreover, kidneys are hypoplastic in both nitrofen-exposed groups and have reduced retinol content, suggesting that a retinoid pathway disruption could be the common mechanism in the pathogenesis of lung and kidney hypoplasia in the nitrofen model of CDH.