Carbon Monoxide Improves Neurologic Outcomes by Mitochondrial Biogenesis after Global Cerebral Ischemia Induced by Cardiac Arrest in Rats.

Mitochondrial dysfunction contributes to brain injury following global cerebral ischemia after cardiac arrest. Carbon monoxide treatment has shown potent cytoprotective effects in ischemia/reperfusion injury. This study aimed to investigate the effects of carbon monoxide-releasing molecules on brain mitochondrial dysfunction and brain injury following resuscitation after cardiac arrest in rats. A rat model of cardiac arrest was established by asphyxia. The animals were randomly divided into the following 3 groups: cardiac arrest and resuscitation group, cardiac arrest and resuscitation plus carbon monoxide intervention group, and sham control group (no cardiac arrest). After the return of spontaneous circulation, neurologic deficit scores (NDS) and S-100B levels were significantly decreased at 24, 48, and 72 h, but carbon monoxide treatment improved the NDS and S-100B levels at 24 h and the 3-day survival rates of the rats. This treatment also decreased the number of damaged neurons in the hippocampus CA1 area and increased the brain mitochondrial activity. In addition, it increased mitochondrial biogenesis by increasing the expression of biogenesis factors including peroxisome proliferator-activated receptor-γ coactivator-1α, nuclear respiratory factor-1, nuclear respiratory factor-2 and mitochondrial transcription factor A. Thus, this study showed that carbon monoxide treatment alleviated brain injury after cardiac arrest in rats by increased brain mitochondrial biogenesis.

Evaluating team-based, lecture-based, and hybrid learning methods for neurology clerkship in China: a method-comparison study.

BACKGROUND: Neurology is complex, abstract, and difficult for students to learn. However, a good learning method for neurology clerkship training is required to help students quickly develop strong clinical thinking as well as problem-solving skills. Both the traditional lecture-based learning (LBL) and the relatively new team-based learning (TBL) methods have inherent strengths and weaknesses when applied to neurology clerkship education. However, the strengths of each method may complement the weaknesses of the other. Combining TBL with LBL may produce better learning outcomes than TBL or LBL alone. We propose a hybrid method (TBL + LBL) and designed an experiment to compare the learning outcomes with those of pure LBL and pure TBL. METHODS: One hundred twenty-seven fourth-year medical students attended a two-week neurology clerkship program organized by the Department of Neurology, Sun Yat-Sen Memorial Hospital. All of the students were from Grade 2007, Department of Clinical Medicine, Zhongshan School of Medicine, Sun Yat-Sen University. These students were assigned to one of three groups randomly: Group A (TBL + LBL, with 41 students), Group B (LBL, with 43 students), and Group C (TBL, with 43 students). The learning outcomes were evaluated by a questionnaire and two tests covering basic knowledge of neurology and clinical practice. RESULTS: The practice test scores of Group A were similar to those of Group B, but significantly higher than those of Group C. The theoretical test scores and the total scores of Group A were significantly higher than those of Groups B and C. In addition, 100% of the students in Group A were satisfied with the combination of TBL + LBL. CONCLUSIONS: Our results support our proposal that the combination of TBL + LBL is acceptable to students and produces better learning outcomes than either method alone in neurology clerkships. In addition, the proposed hybrid method may also be suited for other medical clerkships that require students to absorb a large amount of abstract and complex course materials in a short period, such as pediatrics and internal medicine clerkships.

Correlation between the changes in ambulatory electroencephalography findings and epilepsy recurrence after medication withdrawal among the population in southern China.

Patients suffering from epilepsy need long-term medication. However, after the epilepsy is completely under control, the recurrence rate is high once the drug dose is reduced gradually. The present study investigated the possible correlation between the changes shown by ambulatory electroencephalography (EEG) and epilepsy recurrence after medication withdrawal, and assessed the value of ambulatory EEG findings in predicting the recurrence of epilepsy after medication withdrawal, in 265 patients from Southern China followed up for 5 years. Anticonvulsants were withdrawn until onset had been controlled thoroughly for over 3 years and ambulatory EEG detected no abnormalities. Ambulatory EEG was performed at least once per year, and findings at the first visit, during treatment, and before and after medication withdrawal were compared and analyzed. There were 47 patients with recurrent epilepsy in this study. Patients with normal ambulatory EEG findings at the first visit and during treatment had lower recurrence rate (about 8.1%) compared to patients with epileptic waves (25.0%), and patients with focal epileptic waves in the temporal, occipital, frontal, and parietal lobes, or in multiple areas was even higher. Patients with epileptic waves also showed higher clinical recurrence rate during the follow-up period. Abnormal ambulatory EEG findings are an important indicator of epileptic recurrence, and is of great value in predicting the recurrence of epilepsy after medication withdrawal.

[The epidemiological characteristic of 97,823 cases of pre-hospital medical care in Guangzhou city].

OBJECTIVE: To investigate the epidemiological information of patients in pre-hospital medical care in Guangzhou city, and to explore the characteristics of the patients. METHODS: The data in the year of 2008 were retrieved from the computer database of Guangzhou Emergency Medical Rescue Command Center. RESULTS: (1)In a total of 969 410 calls received, the time of distribution was found to be mainly between 16:00 and 18:00 [11.78% (114 224)], and least frequently between 04:00 and 06:00 [2.40% (23 237)]. (2)Among 109 682 dispatches of ambulances, Baiyun district received the most [26.77% (29 364)], and followed by Haizhu district [18.30% (20 069)], Tianhe district [18.20% (19 962)], respectively. (3)Among 97 823 cases of pre-hospital medical care, death rate of the male patients was higher than the female [amount: 57.65% (56 394) vs. 38.48% (37 641), mortality: 59.17% (3 269) vs. 33.95% (1 876)]. (4)In 9 7823 cases of pre-hospital medical care, trauma constituted the highest rate [34.57% (33 820)], especially traffic accidents [11.56% (11 307)], and the age of most of the patients ranged between 21 and 50. Disease of the nervous system ranged the second, followed by diseases of circulatory system, respiratory system and digestive system, and most of them were over 51 years old, and most frequently above 70. (5)In 97 823 cases of pre-hospital medical care, there were 5 525 deaths (5.65%), in whom the circulatory system diseases ranged first (especially sudden death) [33.07% (1 827)], followed by unclassified diseases [29.79% (1 646)], trauma [15.67% (866)], respiratory diseases [7.48% (413)], and neurological emergency illnesses [5.95% (329)]. The age of deceased was far older than 51, particularly 70. The age of most of the deceased was above 61, and age of traumatic death was 21-40. CONCLUSION: (1) It is very important to reduce the death rate of the middle-old aged patients by strengthening prevention and timely treatment of cardiovascular and cerebrovascular diseases, and improve the medical strategies in emergency care, in order to lower the death rate during emergency.(2)It is very important to emphasize safely in production lines and to strengthen traffic regulations in order to reduce the incidence of trauma, thus it is especially traffic accident, expect that the death rate of trauma could be lowered.

Expressions of SOCS-1 and SOCS-3 in the myocardium of patients with sudden cardiac death.

BACKGROUND: As the regulators of cytokines, suppressors of cytokine signaling (SOCS) play an important role in the inflammation reaction. Some studies found that SOCS-1 and SOCS-3 were involved in the pathogenesis of some inflammatory diseases such as rheumatoid arthritis, inflammatory bowel disease. But the expressions of SOCS in coronary heart disease have not yet been reported. This study aimed to investigate the expression and clinical significance of SOCS-1 and SOCS-3 in the myocardium of patients with sudden cardiac death (SCD). METHODS: Myocardial autopsy specimens were collected from 24 patients at the Forensic Medicine Department of Sun Yat-Sen University, Guangzhou, China between 2005 and 2006. Of them, 9 patients had autopsy findings consistent with coronary atherosclerosis (non-myocardial infarction) leading to SCD (non-MI group), 7 died of acute myocardial infaction (MI group), and 8 died from traffic accidents and trauma (control group). The expressions of SOCS-1 mRNA and SOCS-3 mRNA in the myocardium of the non-MI, MI and control groups were detected using RT-PCR. The levels of SOCS-1 and SOCS-3 proteins were detected using immunohistochemistry. Statistical analyses were performed using SPSS version 13.0 software and the data were analyzed by ANOVA. RESULTS: The expressions of SOCS-1 mRNA and SOCS-3 mRNA in the non-MI and MI groups were significantly higher than those in the control group[(0.788±0.101), (0.741±0.111) vs. (0.436±0.044), (P<0.01); (0.841±0.092), (0.776±0.070) vs. (0.454±0.076), (P<0.01)] respectively. The antibody-positive cells of SOCS-1 protein in the myocardium of the non-MI and MI groups were significantly higher than those in the myocardium of the control group[(320.00±48.48), (347.14±70.88) vs. (42.50±10.35), (P<0.01)] respectively. The antibody-positive cells of SOCS-3 protein in the myocardium of the non-MI and MI groups were significantly higher than those in the myocardium of the control group[(381.11±59.25) vs. (40.00±10.69), (P<0.01)] and[(332.86±111.91) vs. (40.00±10.69), (P=0.001)]. CONCLUSION: The expressions of SOCS-1 and SOCS-3 in the myocardium of patients with SCD from coronary heart disease are significantly increased and contribute to the pathogenesis of SCD.

Changes of the immunological barrier of intestinal mucosa in rats with sepsis.

BACKGROUND: Sepsis has become the greatest threat to in-patients, with a mortality of over 25%. The dysfunction of gut barrier, especially the immunological barrier, plays an important role in the development of sepsis. This dysfunction occurs after surgery, but the magnitude of change does not differentiate patients with sepsis from those without sepsis. Increased intestinal permeability before surgery is of no value in predicating sepsis. The present study aimed to observe the changes of intestinal mucosal immunologic barrier in rat models of sepsis induced by cecal ligation and puncture. METHODS: Sixty Sprague-Dawley rats were randomly divided into a sepsis group (n=45) and a control group (n=15). The rats in the sepsis group were subjected to cecal ligation and puncture (CLP), whereas the rats in the control group underwent a sham operation. The ileac mucosa and segments were harvested 3, 6 and 12 hours after CLP, and blood samples were collected. Pathological changes, protein levels of defensin-5 (RD-5) and trefoil factor-3 (TFF3) mRNA, and lymphocytes apoptosis in the intestinal mucosa were determined. In an additional experiment, the gut-origin bacterial DNA in blood was detected. RESULTS: The intestinal mucosa showed marked injury with loss of ileal villi, desquamation of epithelium, detachment of lamina propria, hemorrhage and ulceration in the sepsis group. The expression of TFF3 mRNA and level of RD-5 protein were decreased and the apoptosis of mucosal lymphocyte increased (P<0.05) in the sepsis group compared with the control group. Significant differences were observed in RD-5 and TFF3 mRNA 3 hours after CLP and they were progressively increased 6 and 12 hours after CLP in the sepsis group compared with the control group (P<0.05, RD-5 F=11.76, TFF3 F=16.86 and apoptosis F=122.52). In addition, the gut-origin bacterial DNA detected in plasma was positive in the sepsis group. CONCLUSION: The immunological function of the intestinal mucosa was impaired in septic rats and further deteriorated in the course of sepsis.

[Risk factors for death due to fungal septicemia and prognostic analysis].

OBJECTIVE: To analyze the incidence, clinical features and the predisposing factors of fungal septicemia, and investigate the risk factors for death due to fungal septicemia and the prognosis of the patients. METHODS: We retrospectively analyzed the clinical data of 91 patients with fungal septicemia diagnosed in the last 17 years, including 60 patients with clinical cure or improvement, and 31 who die of the disease. Based on the results by univariate analysis, the data were analyzed using logistic multiple regression and Fisher's discriminant analysis. RESULTS: Fungal septicemia had many predisposing factors with high mortality rate. Univariate analysis revealed significant differences between the cured/improved cases and the fatal cases for 12 variables, including advanced age, complication by bacterial infection, septic shock, multiple organ dysfunction syndrome (MODS), ICU patients, cortical hormone therapy, surgery, chemotherapy, use of immunopotentiating agents, length of hospital stay before antifungal therapy, time of anti-fungus therapy and types of invasive procedures. Logistic multiple regression analysis showed that the types of invasive procedures, MODS, surgery and prolonged hospital stay before antifungal therapy were the independent risk factors for fungal septicemia-related death. Fisher's linear discriminant equation was established for predicting the prognosis of the disease. CONCLUSION: The types of invasive procedure, MODS, surgery and prolonged hospital stay before antifungal therapy are the independent risk factors for fungal septicemia-related death, and the patients' prognosis can be predicted using Fisher's linear discriminant equation.

Breast cancer resistance protein expression and 5-fluorouracil resistance.

OBJECTIVE: To filtrate breast cancer resistance protein (BCRP)-mediated resistant agents and to investigate clinical relationship between BCRP expression and drug resistance. METHODS: MTT assay was performed to filtrate BCRP-mediated resistant agents with BCRP expression cell model and to detect chemosensitivity of breast cancer tissue specimens to these agents. A high performance liquid chromatography (HPLC) assay was established, and was used to measure the relative dose of intracellular retention resistant agents. RT-PCR and immunohistochemistry (IHC) were employed to investigate the BCRP expression in breast cancer tissue specimens. RESULTS: MTT assay showed that the expression of BCRP increased with the increasing resistance of 5-fluorouracil (5-Fu) (P<0.05, n=3) in the cell model, while HPLC assay indicated that the intracellular retention dose of 5-Fu was significantly correlated with the expression of BCRP (r=-0.897, P<0.05, n=3). A total of 140 breast cancer tissue specimens were collected. BCRP-positive expression was detected in forty-seven specimens by both RT-PCR and IHC. As shown by MTT assay subsequently, the resistance index (RI) of 47 BCRP-positive breast cancer tissue specimens to 5-Fu was 7-12 times as high as that of adjacent normal tissue samples. BCRP expression was related to 5-Fu resistance (R2=0.8124, P<0.01). CONCLUSION: Resistance to 5-Fu can be mediated by BCRP. Clinical chemotherapy for breast cancer patients can be optimized based on BCRP-positive expression.

[Effects of ulinastatin on gut mucosal apoptosis and bacterial translocation in rats with sepsis].

OBJECTIVE: To investigate the effects of ulinastatin on gut mucosal apoptosis and bacterium translocation in a rat model of sepsis. METHODS: Fifty rats were randomly assigned into 4 groups, namely the control (n=5, no operation or drugs), ulinastatin pretreatment (n=15, treated with 25,000 U/kg ulinastatin 2 h before operation), ulinastatin treatment (n=15, treated with 25,000 U/kg ulinastatin 2 h after operation) and sepsis model (n=15, without drug treatment) groups. The rats in the later 3 groups were subjected to cecal ligation and puncture (CLP). At 3, 6 and 12 h after CLP, the rats were sacrificed and the ileum was removed to examine the pathology and apoptosis of the mucosa. The DNA of Bacillus coli in the whole blood was detected using PCR. RESULTS: Sepsis caused of epithelial cell loss in the ileal villi, ulceration and blebbing of the lamina propria. Ulinastatin treatment administered before and after the operation both significantly alleviated these morphological anomalies. The sepsis rats showed significantly increased intestinal mucosal apoptotic index as compared with the other 3 groups (P<0.05). Ulinastatin pretreatment, in comparison ulinastatin treatment 12 h after CLP, significantly increased the intestinal mucosal apoptotic index (P<0.05). Bacillus coli DNA was positive in sepsis and postoperative ulinastatin treatment groups but negative in the control and pretreated groups. CONCLUSION: Increased intestinal musocal apoptosis and gut bacterial translocation occur in rats following sepsis, and ulinastatin can effectively decrease intestinal mucosal apoptosis and inhibit bacterial translocation.

[Risk stratification and prognostic evaluation of patients with pulmonary thromboembolism].

OBJECTIVE: To explore the risk stratification and prognostic evaluation of pulmonary thromboembolism (PTE). METHODS: The clinical data of 46 patients suffering from PTE diagnosed by ventilation perfusion scan or spiral CT pulmonary angiography admitted to our hospital from January 2002 to December 2006 were analyzed retrospectively. RESULTS: The total mortality was 33% (15/46 cases). The mortality in the group whose cardiac troponin I was positive (n=11) was 82% (9/11 cases), 17% (6/35 cases)when troponin I was negative (n=35). The mortality in normal electrocardiogram (ECG) group (n=14) and abnormal group (n=32) was 7% (1/14 cases) and 44% (14/32 cases) respectively. The mortality in the group with right ventricular dilatation (right ventricular diastolic dimension/left ventricular diastolic dimension > or =0.6) as shown by echocardiography (n=20) and without right ventricular dilatation (n=26) right ventricular diastolic dimension/left ventricular diastolic dimension<0.6) was 55% (11/20 cases) and 15% (4/26 cases) respectively. The mortality in the group whose pulmonary arterial obstruction index shown by spiral CT pulmonary angiography <0.6 (n=19) and > or =0.6 (n=11) was 5% (1/19 cases) and 91% (10/11 cases) respectively. The mortality between above groups showed statically significant difference (all P<0.05). CONCLUSION: Cardiac troponin I, ECG, right ventricular dilatation by echocardiography and pulmonary arterial obstruction index by spiral CT pulmonary angiography may be taken as indices for risk stratification and prognostic evaluation of patients with PTE, and they may be helpful in optimizing treatment strategies.

[Analysis of acute cerebral arterial thrombosis with multiple organ dysfunction syndrome].

OBJECTIVE: To investigate the incidence, case fatality and risk factors of acute cerebral arterial thrombosis complicated by multiple organ dysfunction syndrome (MODS). METHODS: A retrospective study was conducted in 830 patients with acute cerebral arterial thrombosis, among whom 89 also developed MODS. RESULTS: The incidence of MODS in these patients was 10.7% with case fatality of 58.4%. The presence of concurrent infection and increased number of organ involved both resulted in higher case fatality. The preceding health status, number of failing organs and score of neurologic impairment were the main fetal factors according to logistic regression analysis. CONCLUSION: MODS usually occurs in two weeks after the onset of acute cerebral arterial thrombosis. Prevention of MODS involves rigorous treatment of the compromised organs and comprehensive systemic therapy in addition to the management of the primary diseases.

[Effect of ulinastatin on apoptosis in ileal mucosa of rats with hemorrhagic shock].

OBJECTIVE: To investigate the effect of ulinastatin on apoptosis in ileal mucosa of rats with hemorrhagic shock. METHODS: A prospective, controlled animal study was performed. The rat model of hemorrhagic shock was replicated according to method described by Chaudry. After 60 minutes period of bleeding, rats were resuscitated by transfusion of shed blood and normal saline. A part of the animals were additionally treated with ulinastatin. The expression of tumor necrosis factor-alpha (TNF-alpha), malondialdehyde (MDA) content in serum, and expression of Bax, Bcl-2, caspase 3 protein in ileal mucosa were determined at different time points after reperfusion. RESULTS: Compared with the normal saline group, the expression levels of TNF-alpha, MDA content in serum, Bax and caspase 3 protein in ileal mucosa during hemorrhagic shock after resuscitation were significantly increased, while Bcl-2 protein was markedly decreased. After fluid resuscitation, obvious increase in MDA, Bcl-2 protein, significant decrease in the level of TNF-alpha, the expression of Bax and caspase 3 protein in ileal mucosa were observed in the ulinastatin group compared with normal saline group. CONCLUSION: Ulinastatin has protective effect on rats with hemorrhagic shock by suppressing the apoptosis in ileal mucosa.

[Effect of goblet cell in rat intestine on the restitution process of the gut barrier after hemorrhagic shock].

OBJECTIVE: To investigate the changes of the goblet cells in the intestine during the restitution process of the gut barrier after hemorrhagic shock. METHODS: Forty-nine Sprague-Dawley rats with body weight of 250-300 g were divided into control group (n=7) and experimental group (n=42). Rats in the experimental group was further divided into 6 groups (n=7 each) according to different time point at 1, 3, 6, 12, 24, and 36 hours after hemorrhagic shock resuscitation. The specimens from ileum tissue were taken to observe the morphological chan ges of the intestinal mucosa. The number of goblet cells was determined by light microscope and/or electron microscope. The contents of trefoil factor family 3 (TFF3) of goblet cells were examined using GC-9A gas chromatographic instrument. RESULTS: After hemorrhagic shock, mucosal epithelial injury was obvious in the small intestine. Tissue restitution was found after 3 hours, and mostly established after 12 hours. Following tissue restitution,the denuded mucosal surface was covered intensively by goblet cells. The number of goblet cells on the intestinal mucosa was reduced significantly from 243+/- 13 at 1 h to 157+/- 9 at 24 h (r=- 0.910, P< 0.01), and returned to normal level at 36 h. In the experimental group, the content of TFF3 in the intestinal mucosa increased significantly at 12 hours, decreased, but was still higher at 24 hours (t=3.24, P< 0.05). CONCLUSIONS: The goblet cells play a key role in the restitution of intestinal mucosa. High expression of TFF3 may facilitate the intestinal mucosal restitution in the early phase.

Functional and morphological changes of the gut barrier during the restitution process after hemorrhagic shock.

AIM: To investigate the functional, morphological changes of the gut barrier during the restitution process after hemorrhagic shock, and the regional differences of the large intestine and small intestine in response to ischemia/reperfusion injury. METHODS: Forty-seven Sprague-Dawley rats with body weight of 250-300 g were divided into two groups: control group (sham shock n = 5) and experimental group (n = 42). Experimental group was further divided into six groups (n = 7 each) according to different time points after the hemorrhagic shock, including 0(th) h group, 1st h group, 3rd h group, 6th h group, 12th h group and 24th h group. All the rats were gavaged with 2 mL of suspension of lactulose (L) (100 mg/2 mL) and mannitol (M) (50 mg/each) at the beginning and then an experimental rat model of hemorrhagic shock was set up. The specimens from jejunum, ileum and colon tissues and the blood samples from the portal vein were taken at 0, 1, 3, 6, 12 and 24 h after shock resuscitation, respectively. The morphological changes of the intestinal mucosa, including the histology of intestinal mucosa, the thickness of mucosa, the height of villi, the index of mucosal damage and the numbers of goblet cells, were determined by light microscope and/or electron microscope. The concentrations of the bacterial endotoxin lipopolysaccharides (LPS) from the portal vein blood, which reflected the gut barrier function, were examined by using Limulus test. At the same time point, to evaluate intestinal permeability, all urine was collected and the concentrations of the metabolically inactive markers such as L and M in urine were measured by using GC-9A gas chromatographic instrument. RESULTS: After the hemorrhagic shock, the mucosal epithelial injury was obvious in small intestine even at the 0(th) h, and it became more serious at the 1st and the 3rd h. The tissue restitution was also found after 3 h, though the injury was still serious. Most of the injured mucosal restitution was established after 6 h and completed in 24 h. Two distinct models of cell death-apoptosis and necrosis-were involved in the destruction of rat intestinal epithelial cells. The number of goblet cells on intestinal mucosa was reduced significantly from 0 to 24 h (the number from 243+/-13 to 157+/-9 for ileum, 310+/-19 to 248+/-18 for colon; r = -0.910 and -0.437 respectively, all P<0.001), which was the same with the large intestine, but the grade of injury was lighter with the values of mucosal damage index in 3 h for jejunum, ileum, and colon being 2.8, 2.6, 1.2, respectively. The mucosal thickness and the height of villi in jejunum and ileum diminished in 1 h (the average height decreased from 309+/-24 to 204+/-23 microm and 271+/-31 to 231+/-28 microm, r = -0.758 and -0.659, all P<0.001; the thickness from 547+/-23 to 418+/-28 microm and 483+/-45 to 364+/-35 microm, r = -0.898 and -0.829, all P<0.001), but there was no statistical difference in the colon (F = 0.296, P = 0.934). Compared with control group, the urine L/M ratio and the blood LPS concentration in the experimental groups raised significantly, reaching the peak in 3-6 h (L/M: control vs 3 h vs 6 h was 0.029+/-0.09 vs 0.063+/-0.012 vs 0.078+/-0.021, r = -0.786, P<0.001; LPS: control vs 3 h vs 6 h was 0.09+/-0.021 vs 0.063+/-0.012 vs 0.25+/-0.023, r = -0.623, P<0.001), and it kept increasing in 24 h. CONCLUSION: The gut barrier of the rats was seriously damaged at the early phase of ischemic reperfusion injury after hemorrhagic shock, which included the injury and atrophy in intestinal mucosa and the increasing of intestinal permeability. Simultaneously, the intestinal mucosa also showed its great repairing potentiality, such as the improvement of the intestinal permeability and the recovery of the morphology at different phases after ischemic reperfusion injury. The restitution of gut barrier function was obviously slower than that of the morphology and there was no direct correlation between them. Compared with the small intestine, the large intestine had stronger potentiality against injury. The reduction of the amount of intestinal goblet cells by injury did not influence the ability of intestinal mucosal restitution at a certain extent and it appeared to be intimately involved in the restitution of the epithelium.