Dental damage: Creating 3D anatomical models to illustrate destructive effects on human teeth.

Forensic odontologists often must identify human remains with damaged teeth. This damage is due to high-impact accidents, violence, or disasters. This 2-part study aimed to create two 3D digital models. They should show the destructive effects of physical and chemical agents on human teeth and popular dental materials. Researchers created an e-survey to investigate how digital models are perceived as an educational tool for Forensic Odontology. Also, a systematic review assessed experimental studies on the effects of high temperature on various prosthodontic materials. According to the results of the survey, most participants (n=69; 79%) agreed that they would find a 3D model useful for training. Participants misidentify images of burned and broken teeth under Ellis and Davey system (1970). The systematic review identified dental implant and dental crown as the most studied prosthodontic materials exposed to heat. The researchers designed dental damage model 1 to represent restored and unrestored burnt teeth, postmortem pink teeth, and traumatic injuries. The dental damage model 2 was created to demonstrate the effects of various types of damage to different prosthetic and restorative dental materials, as well as the impact of acid, water, and burial on restorative materials as additional information. Both models were edited, sculpted and painted using 3D modelling software ZBrush (2020. 1.4) and Blender (version 3.6.2). The dental damage models were uploaded and labelled on Sketchfab (Cédric Pinson, Paris, France). The study's materials could transform the teaching of complex tooth changes.

Respiratory Sarcopenia and Sarcopenic Respiratory Disability: Concepts, Diagnosis, and Treatment.

The condition of muscle fiber atrophy and weakness that occurs in respiratory muscles along with systemic skeletal muscle with age is known as respiratory sarcopenia. The Japanese Working Group of Respiratory Sarcopenia of the Japanese Association of Rehabilitation Nutrition narratively reviews these areas, and proposes the concept and diagnostic criteria. We have defined respiratory sarcopenia as "whole-body sarcopenia and low respiratory muscle mass followed by low respiratory muscle strength and/or low respiratory function." Respiratory sarcopenia can be caused by various factors such as aging, decreased activity, undernutrition, disease, cachexia, and iatrogenic causes. We have also created an algorithm for diagnosing respiratory sarcopenia. Respiratory function decreases with age in healthy older people, along with low respiratory muscle mass and strength. We have created a new term, "Presbypnea," meaning a decline in respiratory function with aging. Minor functional respiratory disability due to aging, such as that indicated by a modified Medical Research Council level 1 (troubled by shortness of breath when hurrying or walking straight up hill), is an indicator of presbypnea. We also define sarcopenic respiratory disability as "a disability with deteriorated respiratory function that results from respiratory sarcopenia." Sarcopenic respiratory disability is diagnosed if respiratory sarcopenia is present with functional disability. Cases of respiratory sarcopenia without functional disability are diagnosed as "at risk of sarcopenic respiratory disability." Functional disability is defined as a modified Medical Research Council grade of 2 or more. Rehabilitation nutrition, treatment that combines rehabilitation and nutritional management, may be adequate to prevent and treat respiratory sarcopenia and sarcopenic respiratory disability.

Utility of weekly docetaxel combined with preoperative radiotherapy for locally advanced esophageal cancer from pathological analysis.

Esophageal squamous cell cancer (ESCC) is a high-grade carcinoma that is treated with multidisciplinary approaches, including chemoradiotherapy (CRT) followed by surgery. Despite some success with these therapies, overall survival remains poor. In order to investigate a newer CRT regimen, we designed a comparative study to evaluate preoperative CRT using docetaxel (DOC) or 5-Fluorouracil and cisplatin (FU+CDDP [FP] therapy) for treatment of resectable ESCC. In a retrospective review of patients with resectable, locally advanced ESCC, 95 patients received preoperative CRT between 2001 and 2007. CRT was administered using either FP (n = 40) or DOC (n = 55). Pathological response and clinical outcomes were compared between the two groups. Hazard ratios and time-to-event analyses were used to assess outcomes; the ratios were controlled by multivariate logistic regression analysis of potential prognostic factors, and survival was presented with Kaplan-Meier curves. In the FP group, a significant curative effect was observed on the basis of pathological examination of postoperative lesions. However, the DOC group presented a significantly better prognosis on the basis of cumulative survival rates. Logistic regression analysis revealed that the presence of five or more lymph node metastases was an independent predictor of reduced survival. Patients with lymph node metastasis exhibited a better prognosis in the DOC group than those in the FP group. Preoperative CRT for locally advanced esophageal cancer using DOC results in similar or better long-term outcomes compared with FP-based CRT. Therefore, CRT using DOC is a promising therapy option for esophageal cancer.

Type I interferon receptor and response to interferon therapy in chronic hepatitis C patients: a prospective study.

The type I interferon (IFN) receptor consists of at least two subunits, IFNAR1 and IFNAR2. We previously found a correlation between IFNAR1 and IFNAR2 expression in liver, and a correlation in IFNAR2 expression, but not in IFNAR1, between liver and peripheral blood mononuclear cells (PBMCs). The aim of this study was to prospectively assess whether IFNAR2 expression levels in PBMCs as well as in liver act as markers for predicting response to IFN therapy in chronic hepatitis C patients. Fifty-two Japanese patients with chronic hepatitis C, were enrolled. IFNAR2 mRNA was quantified using competitive polymerase chain reaction, in liver and PBMC specimens, and of the 52 patients assigned to receive a 6-month course of interferon-alpha therapy, 36 patients who received more than 300 million units of interferon were analysed. IFNAR2 mRNA expression levels were significantly higher in liver than in PBMCs in all 36 patients (P = 0.016). Seventeen sustained virologic responders showed lower pretreatment hepatitis C virus (HCV)-RNA levels (P = 0.017) in serum and higher pretreatment levels of IFNAR2 mRNA in liver (P = 0.007), but not in PBMCs, compared with nonsustained virologic responders. In multivariate analysis, these factors were independently associated with a sustained virologic response (i.e. HCV-RNA level: odds ratio 0.23, 95% CI 0.038-0.864; and IFNAR2 in liver: odds ratio 1.116, 95% CI 1.015-1.227). Hence, IFNAR2 expression levels in liver, but not in PBMCs, is predictive of response to IFN treatment in chronic hepatitis C patients.

Lymph node hyalinization in elderly Japanese.

Lymph node hyalinization has been comprehensively investigated using specimens obtained from elderly Japanese and white Americans. Onion-peel lesions and associated meshwork areas were often found in the medullary sinus of the thoracic node (mediastinal-type hyalinization), while eosinophilic, glassy and spotty lesions were consistently seen in B lymphocyte areas of the pelvic node (pelvic-type hyalinization). The mediastinal-type hyalinization was comprised of thin collagen fibrils (ca 50 nm in diameter), whereas the pelvic-type hyalinization had thick fibrils (ca 150 nm in diameter). This difference seemed to be consistent with a difference in composite collagen fibrils of vascular walls between the thoracic and pelvic regions. The pelvic-type hyalinization was often or sometimes seen in other nodes, such as cervical, axillary, abdominal and inguinal nodes, especially in white Americans. The mediastinal-type hyalinization, usually in combination with a sinus filled with anthracotic macrophages, tended to be observed in Japanese more frequently than in white Americans. Anthracosis seemed to be connected to the pathogenesis of the hyalinization. On the other hand, because the lesion was weakly positive for Factor VIII immunohistochemistry and because lesions were located along thin vessels, the pelvic-type hyalinization seemed to originate from vascular degeneration in the nodal cortex. Due to the high incidence and large proportion in total volume of the node, the hyalinization seems to be one of the major events that diminish the nodal filtration function and ruin the node with aging.

Interferon retreatment reduces or delays the incidence of hepatocellular carcinoma in patients with chronic hepatitis C.

Inhibition of hepatocarcinogenesis is a crucial issue in treating chronic hepatitis C patients, especially those who do not respond completely to interferon therapy. Interferon has been reported to reduce the incidence of hepatocellular carcinoma (HCC) not only in sustained virological responders but also in transient biochemical responders. However, the incidence of HCC increases in 5 years or more after interferon therapy in transient biochemical responders. The aim of this study is to assess whether interferon retreatment reduces the incidence of HCC in chronic hepatitis C patients in whom hepatitis C virus was not eradicated during initial interferon therapy. We enrolled 309 patients who were not sustained virological responders after initial interferon treatment consisting of a total dose of more than 250 megaunits of interferon and were followed for more than 2 years after treatment. Ninety-nine patients received interferon retreatment and 210 did not. Two courses of interferon therapy were administered in 84, three courses in 14 and five courses in one. The incidence of HCC was compared between patients with retreatment and those without. In the clinical characteristics, retreated patients were younger and followed up for a longer time period. The cumulative incidence of HCC was significantly lower in retreated patients. In multivariate analysis, patients' age (P=0.018) and the number of courses of interferon therapy (P=0.022) were independently associated with HCC incidence. These results suggest that interferon retreatment reduces or delays the incidence of HCC in chronic hepatitis C patients who did not completely respond to initial therapy.

Constrained genomic and conformational variability of the hypervariable region 1 of hepatitis C virus in chronically infected patients.

We analysed the genomic and conformational variability of the hypervariable region 1 (HVR1) of the hepatitis C virus (HCV) to evaluate the importance of its biological role. A total of 865 genotype 1b HVR1 subclones were collected from serially sampled sera in 11 patients with chronic hepatitis C, four of whom received interferon therapy. Consequently, 169 distinct sequences were examined for amino acid substitutions as well as hydrophilic or hydrophobic profile at each amino acid position within HVR1. Secondary structure of HVR1 was also predicted by the method of Robson in 90 distinct sequences from eight patients, including three interferon-treated patients. Some positions within the HVR1 were invariable or nearly so as to amino acid substitution. Hydrophilic or hydrophobic residues exclusively predominated at several positions. These constrained amino acid replacement and hydrophilic or hydrophobic profiles were conserved irrespective of interferon therapy, though the frequency of amino acid replacement was greater at almost all amino acid positions within the HVR1 in interferon-treated patients. The quasispecies of HCV showed various secondary structures of HVR1, but many sequences seemed to have common characteristics. beta sheet conformations around both the N-terminus and position 20 (numbered from the NH2 terminus of E2 envelope glycoprotein), and/or coil structures around the C-terminus of HVR1 could be identified. These results suggest that HVR1 amino acid replacements are strongly constrained by a well-ordered structure, in spite of being tolerant to amino acid substitutions, and imply an important biological role of the HVR1 protein in HCV replication.

Device for the removal of button batteries.

OBJECTIVE: There is an increasing number of accidents by erroneous ingestion of button batteries in recent years; the batteries arouse the interest of infants because of their attractive shape and luster. The batteries remaining in the gastrointestinal tract and discharging electric current over a long period of time may induce ulceration or perforation, thus must be carefully considered the selection of appropriate treatment. METHODS: We remove erroneously ingested button batteries with two tubes with ferrite magnets nearly the same size as the button batteries themselves. PATIENTS: Four cases of erroneous ingestion of button batteries. RESULTS: We easily removed button batteries from the stomach within 5 minutes in all cases with two magnet-attached tubes. CONCLUSION: We present this battery removal device together with a literature review, because it seems convenient and useful.

Hepatitis C virus quasispecies and response to interferon therapy in patients with chronic hepatitis C: a prospective study.

We prospectively examined whether the complexity of hepatitis C virus (HCV) quasispecies is related to the response to interferon (IFN) therapy. Among 64 patients who had histologically proven chronic hepatitis and were treated with natural IFN-alpha, 53 patients were analysed. The other 11 patients discontinued therapy because of adverse effects of IFN. The complexity of the hypervariable region 1 (HVR 1) in quasispecies was determined using both clone number determined by fluorescence single-strand conformation polymorphism (SSCP) and nucleotide diversity determined by direct sequencing. These parameters were measured not only before treatment but also at completion and 6 months after therapy, if serum HCV RNA was detectable. This population of patients was different from the general Japanese population with regard to the high prevalence of patients infected with genotype 2a or 2b (49%), who had a higher viral load than those with genotype 1b (P = 0.021). Twenty-two patients (41.5%) were sustained responders. Genotype non-1b (P = 0.0009) and a smaller clone number (P = 0.008) were significantly associated with a sustained response. In multivariate analysis, these variables were independently associated with a sustained response (i.e. genotype: odds ratio 6.84, 95% CI 1.84-30. 12; and clone number: odds ratio 1.26, 95% CI 0.99-1.68). The clone number and nucleotide diversity did not change significantly between pretreatment and at completion or 6 months after therapy. These results suggest that lower complexity of HVR 1 quasispecies predicts a preferable response to IFN therapy that is independent of viral load, especially in the population of the relatively high prevalence of patients infected with genotype 2.

Molecular mechanism of the multiple regulation of the Saccharomyces cerevisiae ATF1 gene encoding alcohol acetyltransferase.

The ATF1 gene encodes an alcohol acetyl transferase (AATase), that catalyses the synthesis of acetate esters from acetyl CoA and several kinds of alcohols. ATF1 transcription is negatively regulated by unsaturated fatty acids and oxygen. A series of analyses of the ATF1 promoter identified an 18 bp element essential for transcriptional activation. Ligation of the 18 bp element into a plasmid carrying the CYC1 promoter deleted UAS-activated transcription and conferred transcriptional repression by unsaturated fatty acids. The 18 bp element contains a binding sequence for Rap1p, which is a transcriptional repressor and activator. In vitro binding studies showed that Rap1p binds to the 18 bp element essential for transcriptional activation. The results of internal deletion studies of the promoter region suggested that there was also a region responsible for ATF1 oxygen regulation. This region contained the consensus binding sequence for the hypoxic repressor Rox1p. In vitro binding studies showed that Rox1p binds to the region responsible for oxygen regulation. To investigate the effect of the hypoxic repressor complex on transcription, ATF1 expression was measured in rox1, tup1 and ssn6 disruptant strains. It was found that rox1, tup1 and ssn6 disruption caused elevated expression of ATF1 under aerobic conditions. Thus, the activation of ATF1 transcription is dependent on Rap1p, and the Rox1p-Tup1p-Ssn6p hypoxic repressor complex is responsible for repression by oxygen. Furthermore, a study of ATF1 expression in a sch9 null mutant suggested that the Sch9p protein kinase is involved in ATF1 trancriptional activation.

Structural elements common to mitosis and apoptosis.

Both mitotic and apoptotic cells display hypercondensation of the chromatin and loss of the nuclear envelope (Lazebnik et al., 1993). Herein, we describe a third similarity between the two processes. We have observed, initially in apoptotic cells of the PC-12 lineage clusters of 40-60 (approximately 50) nm vesicles adjoined by a minor contingent of tubule vesicular elements of 100-200 nm which are indistinguishable from their vesicular counterparts in mitotic PC-12 cells. The clusters of approximately 50 nm vesicles were subsequently observed in all studied rat tissue cells in apoptosis (plasma cells and macrophages, secretory epithelial cells from pancreatic acini, ventral lobe of prostate and mammary gland). Clusters of approximately 50 nm vesicles comparable to those of the PC-12 cells were found in HeLa cells treated with human alfa TNF, in WEHI-3 cells exposed to VM 26 (a teneposide) (Sesso et al., 1997) and in HL-60 cells treated with thapsigargin. PC-12 and HeLa cells affixed to coverslips were double labelled and examined with the fluorescence microscope to reveal simultaneously the disposition of the chromatin with Hoechst stain and the distribution of the fluorescence of Golgi or of Golgi-associated proteins. A common pattern of fluorescence was observed in a minor proportion of apoptotic cells using three different antibodies used. The label frequently appeared as finely dispersed granules in the cytoplasm. In some apoptotic cells, relatively coarse granules were observed. This pattern of label distribution is compatible with the disposition of vesicular clusters we have encountered in apoptotic PC-12 cells sectioned serially or semi serially. In such sections of both mitotic and apoptotic PC-12 cells, we noticed that the conglomerates of 50 nm vesicles were frequently associated with cisternae of the rough ER. Vesicles of similar size were also noted pinching off from the extremities of Golgi cisternae reduced in size. These cisternae diminish in length and width when they are in the process of disassembling at the very beginning of mitosis and in apoptosis.

Leptomycin B inactivates CRM1/exportin 1 by covalent modification at a cysteine residue in the central conserved region.

The cellular target of leptomycin B (LMB), a nuclear export inhibitor, has been identified as CRM1 (exportin 1), an evolutionarily conserved receptor for the nuclear export signal of proteins. However, the mechanism by which LMB inhibits CRM1 still remains unclear. CRM1 in a Schizosaccharomyces pombe mutant showing extremely high resistance to LMB had a single amino acid replacement at Cys-529 with Ser. The mutant gene, named crm1-K1, conferred LMB resistance on wild-type S. pombe, and Crm1-K1 no longer bound biotinylated LMB. (1)H NMR analysis showed that LMB bound N-acetyl-L-cysteine methyl ester through a Michael-type addition, consistent with the idea that LMB binds covalently via its alpha, beta-unsaturated delta-lactone to the sulfhydryl group of Cys-529. When HeLa cells were cultured with biotinylated LMB, the only cellular protein bound covalently was CRM1. Inhibition by N-ethylmaleimide (NEM), an alkylating agent, of CRM1-mediated nuclear export probably was caused by covalent binding of the electrophilic structure in NEM to the sulfhydryl group of Cys-529, because the crm1-K1 mutant showed the normal rate for the export of Rev nuclear export signal-bearing proteins in the presence of not only LMB but also NEM. These results show that the single cysteine residue determines LMB sensitivity and is selectively alkylated by LMB, leading to CRM1 inactivation.

Isolation and characterization of the ATF2 gene encoding alcohol acetyltransferase II in the bottom fermenting yeast Saccharomyces pastorianus.

The ATF2 gene encodes alcohol acetyltransferase II, which catalyses the synthesis of isoamyl acetate from acetyl coenzyme A and isoamyl alcohol. To characterize the ATF2 gene from the bottom fermenting yeast Saccharomyces pastorianus, the S. pastorianus ATF2 gene was cloned by colony hybridization using the S. cerevisiae ATF2 gene as a probe. When an atf1 null mutant strain was transformed with a multi-copy plasmid carrying the S. pastorianus ATF2 gene, the AATase activity of this strain was increased by 2.5-fold compared to the control. The S. pastorianus ATF2 gene has 99% nucleic acid homology in the coding region and 100% amino acid homology with the S. cerevisiae ATF2 gene. Southern blot analysis of chromosomes separated by pulse-field gel electrophoresis indicated that the ATF2 gene probe hybridized to chromosome VII in S. cerevisiae and to the 1100 kb chromosome in S. pastorianus. As S. pastorianus is thought to be a hybrid of S. cerevisiae and S. bayanus, the S. bayanus-type gene, which has a relatively low level of homology with the S. cerevisiae-type gene, is also usually detected. Interestingly, an S. bayanus-type ATF2 gene could not be detected. These results suggested that the cloned ATF2 gene was derived from S. cerevisiae. Analysis using an ATF2-lacZ fusion gene in S. pastorianus showed that expression of the ATF2 gene was relatively lower than that of the ATF1 gene and that it is repressed by aeration but activated by the addition of unsaturated fatty acids. The S. pastorianus ATF1, Lg-ATF1 and ATF2 Accession Numbers in the DDBJ Nucleotide Sequence Database are D63449, D63450 and D86480, respectively.

Transcriptional co-regulation of Saccharomyces cerevisiae alcohol acetyltransferase gene, ATF1 and delta-9 fatty acid desaturase gene, OLE1 by unsaturated fatty acids.

The ATF1 gene encodes an alcohol acetyl transferase which catalyzes the synthesis of acetate esters from acetyl CoA and several kinds of alcohols. ATF1 expression is repressed by unsaturated fatty acids or oxygen. Analysis using ATF1-lacZ fusion plasmid revealed that ATF1 gene expression is widely repressed by a variety of unsaturated fatty acids, and the degree of ATF1 transcriptional repression varies according to the structure of the unsaturated fatty acids. Interestingly, it was noted that the degree of ATF1 transcriptional repression was related to the melting point of unsaturated fatty acids added to the medium. The OLE1 gene, which encodes delta-9 fatty acid desaturase, has been reported to be repressed by unsaturated fatty acids. Transcription of OLE1 was also repressed by a wide variety of unsaturated fatty acids under anaerobic conditions. The degree of transcriptional repression of OLE1 was also related to the melting point of the added unsaturated fatty acids. Therefore, it is considered that ATF1 and OLE1 transcription are regulated in response to cell membrane fluidity. As has been reported for OLE1, the repression of ATF1 by unsaturated fatty acids was relieved in a disruptant carrying a faa1 and faa4 double mutation, two fatty acid activation genes. However, the ATF1 transcript in this double gene disruptant was repressed by oxygen. These results suggested that ATF1 transcription was co-regulated by the same mechanism as the OLE1 gene and that unsaturated fatty acids and oxygen repressed the ATF1 transcript by a different regulation pathway.

Leptomycin B targets a regulatory cascade of crm1, a fission yeast nuclear protein, involved in control of higher order chromosome structure and gene expression.

The molecular action of leptomycin B (LMB), an agent inducing arrest of the eukaryotic cell cycle at G1 and G2 phases, was investigated by analyzing an LMB resistance gene of Schizosaccharomyces pombe. A genomic library of an LMB-resistant mutant was screened for LMB resistance, and a DNA fragment containing an open reading frame (ORF) of 1078 amino acids was cloned on a multicopy vector. The plasmid was found to confer drug resistance specifically to LMB. Nucleotide sequencing revealed that the ORF was a mutant gene for the essential nuclear protein crm1, which had been reported to complement a cold-sensitive mutation causing deformed nuclear morphology. The gene product named crm1-N1 had two amino acid replacements (Gly-503 to Asp and Met-546 to Ile). Two allelic mutants of crm1 (crm1-809 and crm1-119) were found to be hypersensitive and resistant, respectively, to LMB. Nuclear morphology of the cold-sensitive crm1-809 mutant at the restrictive temperature was almost the same as that of the wild-type cells treated with LMB. Furthermore, a low concentration of LMB induced the intracellular accumulation of a 25-kDa protein in the wild-type cells, which was immunologically identical to the protein accumulating in the crm1-809 mutant cells. These results strongly suggest that LMB primarily inhibits the function of the crm1 gene which is required for maintaining higher order chromosome structures, correct gene expression, and cell growth in the fission yeast.

Regulation of LDL receptor expression by luminal sterol flux in CaCo-2 cells.

The regulation of expression of the intestinal low density lipoprotein (LDL) receptor by luminal (apical) sterol flux was investigated in the human intestinal cell line CaCo-2. Cells were cultured on semipermeable micropore filters, which separated an upper and lower well. To the apical media were added solutions containing either taurocholate micelles alone or micelles containing sterols. Because of an efflux of cholesterol, which occurred from cells incubated with micelles alone, LDL receptor mRNA levels increased threefold. With an influx of micellar sterols, receptor mRNA levels decreased in a dose-dependent manner. Synthesis and degradation of the LDL receptor were addressed by pulse-chase experiments. In cells incubated with micelles containing 25-hydroxycholesterol, the rate of receptor synthesis was significantly decreased, whereas the rate of receptor turnover remained unchanged. As assessed by immunoblots and steady-state labeling of proteins followed by immunoprecipitation of the LDL receptor, cells incubated with micellar 25-hydroxycholesterol contained substantially less receptor protein. These cells also bound and degraded less LDL. In contrast, in cells incubated with micelles alone, the rate of receptor synthesis was increased and cells contained more LDL receptor protein, although this was not reflected in an increased in LDL binding. The results suggest that LDL receptor expression in CaCo-2 cells is regulated by luminal sterol flux and that this regulation occurs at the level of transcription.

Regulation of gene expression and synthesis and degradation of 3-hydroxy-3-methylglutaryl coenzyme A reductase by micellar cholesterolin CaCo-2 cells.

To investigate whether, and by what mechanisms, luminal (dietary) cholesterol regulates cholesterol synthesis in human intestinal cells, HMG-CoA reductase activity, gene expression, synthesis, and degradation were investigated in CaCo-2 cells exposed to taurocholate micelles containing cholesterol. In cells incubated with cholesterol solubilized in 5 mM taurocholate and 30 microM monoolein, HMG-CoA reductase activity was decreased. 25-Hydroxycholesterol, delivered to the cells in the same manner as native cholesterol, was significantly more potent in inhibiting reductase activity and was used, therefore, to investigate mechanisms for sterol regulation. Cells incubated with taurocholate micelles without cholesterol lost cellular cholesterol into the medium causing an increase in HMG-CoA reductase activity and enzyme mass. Although steady-state levels of HMG-CoA reductase mRNA were increased under conditions of cholesterol efflux, synthesis rates of reductase protein were not increased. An increase in activity and enzyme mass in cells incubated with micelles alone, however, was accompanied by a significant decrease in the rate of degradation of reductase protein. In contrast, sterol influx from taurocholate micelles was associated with a marked decrease in HMG-CoA reductase activity and mass without altering mRNA levels except at high concentrations of the polar sterol which did decrease reductase mRNA levels by 50%. The absorption of apical sterol resulted in a significant decrease in the translational efficiency of reductase mRNA and a modest increase in the rate of degradation of the enzyme. Thus, although the primary function of the enterocyte is to transport luminal (dietary) cholesterol to other tissues of the body, apically derived cholesterol enters metabolic pools within the cell which regulates its own cholesterol synthesis. Dietary cholesterol, therefore, will regulate the contribution to the total body cholesterol pool of endogenously derived cholesterol from the intestine. The mechanism for this regulation of intestinal HMG-CoA reductase by luminal cholesterol occurs primarily at the post-transcriptional level.