Statistical results
At the same time, there was a significant difference in cytokine production between the two groups (F = 40.332, P = 0.001). The test results of cytokines expression in different organs of the NEC group and control group were as follows (Table 1). Except for PAF expressed in the liver, there was a significant difference in other control groups (P < 0.05).
There was no significant difference in Bax, PCNA and PAF in the three control groups at different days (P = 0.459, 1.000, 0.923, respectively). In NEC group, the difference of Bax mean from day 1 to day 7 in each organ was statistically significant (F = 3.154, P = 0.017), the difference of PCNA mean from day 1 to day 7 in each organ was statistically significant (F = 5.141, P = 0.001), the difference of PAF mean from day 1 to day 7 in colon and ileum was statistically significant (F = 4.300, P = 0.039), but the difference of PAF mean from day 1 to day 7 in lung, liver and kidney was not statistically significant (F = 2.080, P = 0.121). For the statistical significance of the mean value of each tissue of each group, we used LSD to test them (Table 2). The test results were used for time trend analysis.
Pathological changes of colonic, ileal, lung, liver and kidney injury induced by NEC
On the 1st day after the establishment of the NEC model, we observed intestinal villi falling off, structure disappearance caused by necrosis, submucosal and muscular oedema, intestinal wall congestion, hemorrhage, and necrosis accompanied by infiltration by many inflammatory cells, mainly neutrophils. Histological scores centred at 3 and 4 points on the 1st day, but decreased to 2 points by the 3rd to 5th day, and became <1 on the 7th day.
In the NEC group, on the 1st day after modeling, pulmonary epithelium, pulmonary interstitial and renal interstitial oedema were accompanied with inflammatory cell infiltration, and inflammatory exudates were seen in the alveolar cavities and bronchi, vacuolar degeneration of hepatocytes, infiltration of inflammatory cells around necrotic foci, ischemic changes of glomeruli and obvious oedema of the proximal convoluted tubule cells. On the 3rd day, alveolar walls continued to thicken, interstitial oedema was prominent, vacuolar degeneration of the liver was alleviated, necrosis of the liver was reduced, the cytoplasm was still loose, glomerular congestion was obvious, and tubular cells were still edematous. On the 5th day, pulmonary oedema and interstitial thickening were significantly alleviated. By the 7th day, alveolar inflammatory exudation and absorption were more visible, hepatic inflammatory cell infiltration was reduced, and glomerular congestion and tubular oedema were significantly alleviated.
Bax expression in colonic, ileal, lung, liver and kidney
Bax was expressed in intestinal villi epithelial cells, bronchial epithelial cells, inflammatory cells in the pulmonary interstitium and the alveolar area, hepatocytes, renal corpuscles, tubules and medulla. The expression of Bax in the intestinal tract of the NEC group was stronger than that in the control group. Bax expression gradually decreased with time and reached a minimum on the 7th day. The expression of Bax in lung, liver and kidney in the NEC group was higher than that in the control group (P< 0.05). Among them, in the lung, the expression of Bax showed a trend of increasing gradually from the 1st day to the 3rd day, and maintained at a high level in the first 5 days. In the liver, the expression of Bax decreased gradually from the 1st day to the 5th day, and then stabilized. In the kidney, the expression of Bax decreased gradually from the 1st day to the 3rd day, then tended to be stable (Figure 1).
PCNA expression in colonic, ileal, lung, liver and kidney
PCNA is expressed in intestinal epithelial cells, lung epithelium, hepatocytes, interstitial lung, renal cortex and tubular nucleus of the renal corpuscle. In the NEC group, the expression of PCNA on the 1st day after modeling was lower than that of the control group. Expression gradually increased to the 4th and 5th day. Quantitative analysis showed that the expression of PCNA in lung, liver and kidney in the NEC group was higher than that in the control group (P< 0.05), except for the lower expression of PCNA in liver on Day 1. The expression of PCNA in the lungs of the NEC group was higher than that of the control group on the 1st day after modeling, and gradually increased to the 3rd day and then decreased to the 7th day. The expression in the liver gradually increased up to Day 3 and remained stable. The expression increased gradually in the kidney (Figure 2).
PAF expression in colonic, ileal, lung, liver and kidney
PAF was expressed in intestinal villi epithelial cells, bronchial epithelial cells, inflammatory cells in the lung interstitium and alveolar area, hepatocytes, renal corpuscles, renal tubules and medulla. In the NEC group, expression of PAF was higher than that of the control group on the 1st day, then increased gradually up to the 4th day, after which expression began to decrease and approached normal levels by the 7th day. In the liver, it increased gradually from the 2nd day to the 4th day, and then decreased gradually. However, 1-7 days after the termination of NEC induction, its expression in the kidney was stable. Quantitative analysis showed that the expression of PAF in the lung and liver of the NEC group was higher than that of the control group (P< 0.05), but there was no significant difference in the expression of PAF in the kidney (P> 0.05) (Figure 3).