| In face of severe rice contamination with the heavy metal cadmium(Cd)and its potential human health hazards from long-term low-dose exposure,it is extremely important to study the intestinal absorption,organ accumulation,urinary and fecal excretion and toxic damage of the contaminant Cd in rice staple matrices,and to conduct scientific dietary exposure assessment and intervention for its regulation.Brown rice and white rice are the two main forms of rice staple food utilization,and compared with white rice,brown rice retains richer nutrients and trace components,which can be better used as a model of rice staple food matrix model.Therefore,in this paper,we investigated the absorption,distribution,excretion and damage to the organism in Sprague Dawley(SD)female rats after short-and long-term exposure to contaminant Cd in two rice staple matrices,brown rice(BR)and white rice(WR),and the main findings and conclusions of this thesis are as follows.1.By studying the absorption and excretion of natural Cd-contaminated brown rice(cBR)and white rice(cWR)in adult female rats after 24 h short-time intake,we found that although the dose of Cd exposure in the cBR group was 8.61μg/kg.bw,which was higher than that in the cWR group at 6.30 μg/kg.bw,the total maximum absorption of Cd in the gastrointestinal tract of rats in the cBR was about 10%,which occurred at 2 h;correspondingly,the highest gastrointestinal absorption rate of Cd in the cWR group was about 15%,which occurred 1 h after intake,it can be seen that Cd was more easily absorbed by the gastrointestinal tract of rat in cWR than cBR.The main absorption site of Cd in gastrointestinal tract of rat from both rice matrices was duodenum,and the order of Cd concentration in each intestinal segment was duodenum>jejunum and ileum>cecum>stomach>colon.The absorption kinetics showed that the AUClast value of Cd in the gastrointestinal tract of rats in the cBR group(1.44 h mg/kg)was 1.4 times lower than that in the cWR group(2.02 h mg/kg),and the HL_Lambda_z value(47.39 h)was 2.5 times higher than that in the cWR group(18.75 h),indicating that rats in the cWR group absorbed more Cd and eliminated it from the gastrointestinal tract or transit time was shorter,and it entered the body circulation through the gastrointestinal tract more quickly.Therefore,the main reason for inhibiting the absorption of Cd in the gastrointestinal tract of rats in the cBR group was probably its richness in dietary fiber and/or fat.The excretion of Cd in the rice matrix of both groups was mainly through feces instead of urine,and the excretion rates ranged from 15.00%to 55.09%(mean 30.94%)in the cBR group and 21.60%to 27.38%(mean 24.52%)in the cWR group from 0 to 24 h after intake.2.By studying the absorption,excretion and distribution of natural Cdcontaminated brown rice(cBR-test)and white rice(cWR-test)after 45 d of long-term intake in young growth-aged female rats,it was found that the duodenum remained the main site of Cd absorption,followed by the cecum.Cd concentration at the cecum of rats in the cWR-test group was extremely significantly higher than that in the cBR-test group(P<0.001).Cd in both rice matrices accumulated mainly in the kidney and liver of rats,with the Cd concentration in the kidney being about 2.5 times higher than that in the liver,while the net Cd content in the liver was about twice as high as that in the kidney.cWR-test group rats had higher renal Cd content and the sum of liver+kidney accumulation rate than cBR-test.The magnitude of Cd concentration in other organs were pancreas(0.2 mg/kg)>spleen>ovary+fallopian tube+uterus>lung>heart>brain(not detected).The net fecal Cd excretion in the cBR-test group was significantly higher than that in the cWR-test group,which was mainly presumed that dietary fiber promoted the fecal excretion of rats;the Cd excreted through urine in the 45-d test was still negligible.3.By studying the damage to the organism after 45 d long-term intake of natural Cd-contaminated brown rice(cBR-test)and white rice(cWR-test)in young growthaged female rats,it was found that for the serum biochemical indexes in rats,the indexes that showed abnormalities in the cBR-test group compared with the control group were serum aspartate aminotransferase(AST),alkaline phosphatase(ALP),creatine kinase(CK)and γ-glutamyl transferase(γ-GT)levels were increased,while creatinine(CREAS)and urea(UREA)were decreased;in the cWR-test group,the levels of alanine aminotransferase(ALT),AST,CK,CREA-S and uric acid(UA)were increased,while total bilirubin(T-Bil-2)was decreased,indicating that the serum biochemical indexes were disturbed in these two groups of rats,liver and kidney dysfunction occurred.For hormone levels,compared with the non-Cd-contaminated rice control intake groups(cBR-con and cWR-con),serum estradiol(E2)decreased significantly in both cBR-test and cWR-test groups,and progesterone(P)tended to increase in the cWR-test group,indicating that long-term intake of Cd in the rice matrix caused dysregulation of sex hormone levels and endocrine disorders in female rats during the growth period.disturbance.It may be due to the obvious accumulation of Cd in ovaries+fallopian tubes+uterus,which induced dysfunction of sex hormone secretion in ovarian follicles.For rat gastrointestinal histopathology,a small amount of inflammatory cell infiltration was observed in the lamina propria of the duodenum and cecum in the 20%cWR-test group;inflammatory cell infiltration was observed in the lungs of rats in the 40%cBRtest and 20%cWR-test groups;vacuolated lesions were observed in the liver of rats in the 100%cBR-test and 100%cWR-test groups;and vacuolated lesions were observed in the kidneys of rats in the 40%cWR-test groups.It showed that Cd was able to produce histopathological damage hazard in the experimental group rats,and the degree and extent of hazard produced by Cd in the cWR-test matrix was higher than that in the cBR-test group.The differences in the absorption,distribution,excretion and damage of contaminant Cd in rats in the two rice matrices,brown rice and white rice,may be mainly due to the fact that cBR contains more macromolecules,such as dietary fiber,which leads to the slow or incomplete release of Cd from the matrix,or inhibits the digestive enzyme reaction by binding to Cd,thus reducing the intestinal absorption of Cd.At the same time,it can stimulate intestinal peristalsis to increase the number of stools and promote the excretion of Cd from the feces;reduce the accumulation of Cd in the body while mitigating Cd damage to the body.In general,Cd in the rice matrix is easily absorbed,especially in female rats during the growth period,and the resulting damage to the organism should be given sufficient attention. |
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