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[Effect of food allergy early in life on visceral hyperalgesia in the developing rats and role of substance P abnormal expression in colon].

OBJECTIVE
To explore the effect of food allergy (FA) on the development of visceralgia sensibility and the substance P (SP) expression in colon of developing rats with FA.


METHOD
Three-week old female Sprague-Dawley (SD) rats were randomly divided into two groups (n = 10 in each). The rats in FA group were sensitized with ovalbumin (OVA) 40 µg and Al(OH)3 1 mg suspension solution (0.2 ml) intraperitoneal (i.p.) injection on day 0, only OVA 40 µg solution i.p. on day 2, 4, 7, 9, 11, respectively, and the rats were challenged by gavage with OVA solution 30 mg (2 ml) on day 20, 24, 28, 30. The rats in non-sensitized (NS) group were not challenged except handled in the same ways. The serum OVA-IgE were determined by enzyme-linked immuno sorbent assay (ELISA) on day 0, 30. Jejunum segments were used to observe morphological structure, the expression of eosinophils, and the density and the percentage of degranulation of mast cells (MC). The rats were appraised for the pain sensibility of intestinal tract under colorectal distension irritation by the electrophysiological method on external oblique in the 18-24 hr after the last challenge. Colons were used to analyze the expression of SP through immunohistochemical staining and computer image analyzing system.


RESULT
The serum OVA-IgE concentration and the eosinophils, mast cell, the percentage of mast cells degranulation in FA group were more than NS group (P < 0.01). The amplitudes of spike external oblique muscle of abdomen (EOMA, µV) of the FA group under the colorectal distension (CRD) pressures at 0, 15, 30, 45, 60, 75 mm Hg were (17.74 ± 0.72), (18.63 ± 1.72), (22.55 ± 1.70), (28.63 ± 7.00), (33.97 ± 7.34), (37.26 ± 8.40), and (17.43 ± 1.18), (17.27 ± 1.16), (17.73 ± 1.42), (19.55 ± 3.54), (23.29 ± 5.46), (25.20 ± 4.75) in NS group. With the CRD pressure increased, the amplitudes of spike EOMA increased significantly. There were significant differences between groups under the CRD pressures at 30, 45, 60, 75 mm Hg (F = 47.470, 13.367, 13.317, 15.390, P < 0.01). The expressions of colons SP in FA group and NS group are 247.12 ± 90.83 and 103.90 ± 58.94, respectively (t = 4.183, P < 0.01).


CONCLUSION
Sensitization through i.p. pathway and challenge by gavage with OVA in early life could result in FA in young SD rats. FA in early life enabled the amplitudes of spike EOMA and the expression of colons SP increase significantly. It may be related to increase in amount and degranulation of MC and SP abnormal expression in colon, which could lead to the development of visceralgia sensibility.