Biomedical subjects

M K Bennett

Publications and source records attributed to M K Bennett.

At least 55 records · Page 3Linked to original sources

PubMed1996

Identification of SNAP receptors in rat adipose cell membrane fractions and in SNARE complexes co-immunoprecipitated with epitope-tagged N-ethylmaleimide-sensitive fusion protein.

The vesicle-associated membrane proteins [VAMPs; vesicle SNAP receptors (v-SNAREs)] present on GLUT4-enriched vesicles prepared from rat adipose cells [Cain, Trimble and Lienhard (1992) J. Biol. Chem. 267, 11681-11684] have been identified as synaptobrevin 2 (VAMP 2) and cellubrevin (VAMP 3) by using isoform-specific antisera. Additional antisera identify syntaxins 2 and 4 as the predominant target membrane SNAP receptors (t-SNAREs) in the plasma membranes (PM), with syntaxin 3 at one-twentieth the level. Syntaxins 2 and 4 are enriched 5-10-fold in PM compared with low-density microsomes (LDM). Insulin treatment results in an 11-fold increase in immunodetectable GLUT4 in PM and smaller (approx. 2-fold) increases in VAMP 2 and VAMP 3, whereas the subcellular distributions of the syntaxins are not altered by insulin treatment. To determine which of the SNAP receptors (SNAREs) in PM might participate in SNARE complexes with proteins from GLUT4 vesicles, complexes were immunoprecipitated with anti-myc antibody from solubilized membranes after the addition of myc-epitope-tagged N-ethylmaleimide-sensitive fusion protein (NSF) and recombinant alpha-soluble NSF attachment protein (alpha-SNAP). These complexes contain VAMPs 2 and 3 and syntaxin 4, but not syntaxins 2 or 3. Complex formation requires ATP and is disrupted by ATP hydrolysis. When all membrane fractions are prepared from basal cells, few or no VAMPs and no syntaxin 4 are immunoprecipitated in SNARE complexes obtained from LDM alone (or from immunoisolated GLUT4 vesicles). The content of syntaxin 4 depends on the presence of PM, and participation of VAMPs 2 and 3 is enhanced 4-6-fold by the addition of solubilized GLUT4 vesicles to PM. The latter increase is greater than can be explained by the 2-fold higher levels of VAMPs added to the reaction mixture. When all membrane fractions are prepared from insulin-stimulated cells, SNARE complexes formed from PM alone contain similar levels of syntaxin 4 but 5-6-fold higher levels of VAMPs 2 and 3 compared with PM alone from basal cells. Addition of GLUT4 vesicle proteins to PM from insulin-treated cells results in a further 2-fold increase in VAMP 2 recovered in SNARE complexes. Therefore the VAMPs in PM of insulin-treated but not basal cells, and in GLUT4-vesicles from cells in either condition, are in a form that readily forms a SNARE complex with PM t-SNAREs and NSF. Insulin seems to activate PM and/or GLUT4 vesicles so as to increase the efficiency of SNARE complex formation.

Adipose Tissue↗

PubMed1996

Functional interaction of syntaxin and SNAP-25 with voltage-sensitive L- and N-type Ca2+ channels.

We have used an electrophysiological assay to investigate the functional interaction of syntaxin 1A and SNAP-25 with the class C, L-type, and the class B, N-type, voltage-sensitive calcium channels. Co-expression of syntaxin 1A with the pore-forming subunits of the L- and N-type channels in Xenopus oocytes generates a dramatic inhibition of inward currents (>60%) and modifies the rate of inactivation (tau) and steady-state voltage dependence of inactivation. Syntaxin 1-267, which lacks the transmembrane region (TMR), and syntaxin 2 do not modify channel properties, suggesting that the syntaxin 1A interaction site resides predominantly in the TMR. Co-expression of SNAP-25 significantly modifies the gating properties of L- and N-type channels and displays modest inhibition of current amplitude. Syntaxin 1A and SNAP-25 combined restore the syntaxin-inhibited N-type inward current but not the reduced rate of inactivation. Hence, a distinct interaction of a putative syntaxin 1A-SNAP-25 complex with the channel is apparent, consistent with the formation of a synaptosomal SNAP receptors (SNAREs) complex. The in vivo functional reconstitution: (i) establishes the proximity of the SNAREs to calcium channels; (ii) provides new insight into a potential regulatory role for the two SNAREs in controlling calcium influx through N- and L-type channels; and (iii) may suggest a pivotal role for calcium channels in the secretion process.

Animals↗

PubMed1996

Characterization and subcellular localization of target membrane soluble NSF attachment protein receptors (t-SNAREs) in macrophages. Syntaxins 2, 3, and 4 are present on phagosomal membranes.

Phagosomes formed during ingestion of microorganisms by leukocytes undergo a rapid maturation, generating an acidic, microbicidal organelle. Maturation requires interactions with intracellular vesicles that dock and fuse preferentially with the phagosomal membrane. The basis of specificity of vesiculo-phagosomal interaction has not been elucidated. By contrast, the molecular basis of vesicular fusion in other systems is better understood. At neural synapses, vesicular docking and fusion to the plasma membrane are mediated by a protein complex including syntaxin 1. We explored whether macrophages contain syntaxins, and whether selective fusion of vesicles with the phagosome results from the accumulation of syntaxins in the phagosomal membrane. Isoform-specific Abs were utilized to demonstrate utilized to demonstrate that syntaxins 2, 3, and 4, but not syntaxin 1, are present in murine and human macrophages. Biochemical characterization demonstrated the presence of these syntaxins on microsomes, where they are integral membrane proteins. Subcellular localization using confocal immunofluorescence microscopy demonstrated that syntaxins 3 and 4 are present on the plasma membrane as well as on intracellular vesicles. Importantly, phagosomes isolated by fractionation were shown by immunoblotting to contain syntaxins 2, 3, and 4, suggesting that they may participate in phagosomal maturation. The density of the syntaxins on the phagosomal membrane was found to be comparable with that on the surface membrane. This suggests that preferential fusion of vesicles with the phagosomal membrane is not the result of segregation of the syntaxins to this organelle. Instead, local generation of second messengers in the vicinity of the phagosomal membrane may trigger focal fusion.

Animals↗

PubMed1996

Evidence that syntaxin 1A is involved in storage in the secretory pathway.

Syntaxin 1A is a nervous system-specific protein thought to function during the late steps of the regulated secretory pathway by mediating the docking of secretory vesicles with the plasma membrane. We have examined the effects of transiently overexpressing syntaxin 1A on protein secretion in constitutively secreting cell lines that do not normally express the protein. Syntaxin 1A showed the constitutive release of marker proteins human growth hormone (hGH) and vesicular stomatitis virus glycoprotein from COS-1 cells, increasing the intracellular half-life of human growth hormone from 90 min to 18 h. A similar effect was observed in HEK 293 cells. Immunofluorescence microscopy revealed that these secretory proteins were concentrated in the periphery of the cell. The effect was specific for the full-length neuronal protein. Neither a syntaxin 1A variant which lacks a membrane attachment domain nor syntaxin 2 caused the cells to retain human growth hormone. The effect of syntaxin 1A was partially reversed by incubating the cells with botulinum type C1 neurotoxin, which specifically cleaves syntaxin 1A. Release of human growth hormone from syntaxin 1A-expressing cells was maintained during a blockade of protein synthesis, suggesting that the hormone was being released from a pool of stored vesicles which accumulated before the addition of cycloheximide. The existence of a post-Golgi storage compartment in syntaxin 1A-expressing cells was confirmed using brefeldin A to collapse the Golgi stacks in both HEK 293 and COS-1 cells. Brefeldin A rapidly blocked growth hormone release in control cultures while having no effect on release in cells expressing syntaxin 1A. Reducing the temperature to 19 degrees C, which inhibits transport from the trans-Golgi network, also inhibited hGH secretion from cells without syntaxin 1A but had little effect on hGH secretion from cells with syntaxin 1A. The present experiments indicate that syntaxin 1A enables the storage of vesicles which would otherwise be immediately released.

Animals↗

PubMed1996

Sterol regulation of acetyl coenzyme A carboxylase: a mechanism for coordinate control of cellular lipid.

Transcription from the housekeeping promoter for the acetyl coenzyme A carboxylase (ACC) gene, which encodes the rate-controlling enzyme of fatty acid biosynthesis, is shown to be regulated by cellular sterol levels through novel binding sites for the sterol-sensitive sterol regulatory element binding protein (SREBP)-1 transcription factor. The position of the SREBP sites relative to those for the ubiquitous auxiliary transcription factor Sp1 is reminiscent of that previously described for the sterol-regulated low density lipoprotein receptor promoter. The experiments provide molecular evidence that the metabolism of fatty acids and cholesterol, two different classes of essential cellular lipids, are coordinately regulated by cellular lipid levels.

Acetyl-CoA Carboxylase↗

PubMed1996

Differential localization of syntaxin isoforms in polarized Madin-Darby canine kidney cells.

Syntaxins, integral membrane proteins that are part of the ubiquitous membrane fusion machinery, are thought to act as target membrane receptors during the process of vesicle docking and fusion. Several isoforms of the syntaxin family have been previously identified in mammalian cells, some of which are localized to the plasma membrane. We investigated the subcellular localization of these putative plasma membrane syntaxins in polarized epithelial cells, which are characterized by the presence of distinct apical and basolateral plasma membrane domains. Syntaxins 2, 3, and 4 were found to be endogenously present in Madin-Darby canine kidney cells. The localization of syntaxins 1A, 1B, 2, 3, and 4 in stably transfected Madin-Darby canine kidney cell lines was studied with confocal immunofluorescence microscopy. Each syntaxin isoform was found to have a unique pattern of localization. Syntaxins 1A and 1B were present only in intracellular structures, with little or no apparent plasma membrane staining. In contrast, syntaxin 2 was found on both the apical and basolateral surface, whereas the plasma membrane localization of syntaxins 3 and 4 were restricted to the apical or basolateral domains, respectively. Syntaxins are therefore the first known components of the plasma membrane fusion machinery that are differentially localized in polarized cells, suggesting that they may play a central role in targeting specificity.

Animals↗

PubMed1996

Distinct cellular locations of the syntaxin family of proteins in rat pancreatic acinar cells.

Syntaxins are cytoplasmically oriented integral membrane soluble NEM-sensitive factor receptors (SNAREs; soluble NEM-sensitive factor attachment protein receptors) thought to serve as targets for the assembly of protein complexes important in regulating membrane fusion. The SNARE hypothesis predicts that the fidelity of vesicle traffic is controlled in part by the correct recognition of vesicle SNAREs with their cognate target SNARE partner. Here, we show that in the exocrine acinar cell of the pancreas, multiple syntaxin isoforms are expressed and that they appear to reside in distinct membrane compartments. Syntaxin 2 is restricted to the apical plasma membrane whereas syntaxin 4 is found most abundantly on the basolateral membranes. Surprisingly, syntaxin 3 was found to be localized to a vesicular compartment, the zymogen granule membrane. In addition, we show that these proteins are capable of specific interaction with vesicle SNARE proteins. Their nonoverlapping locations support the general principle of the SNARE hypothesis and provide new insights into the mechanisms of polarized secretion in epithelial cells.

Animals↗

PubMed1996

Syntaxin 4 in 3T3-L1 adipocytes: regulation by insulin and participation in insulin-dependent glucose transport.

Syntaxins are thought to be membrane receptors that bind proteins of the synaptobrevin/vesicle-associated membrane protein (VAMP) family found on transport vesicles. Recently, we detected synaptobrevin II and cellubrevin on immunopurified vesicles containing the glucose transporter 4 (GLUT4) in insulin-responsive cells. In an effort to identify the plasma membrane receptors for these vesicles, we now examine the expression of syntaxins in the 3T3-L1 adipocyte cell line. Neither syntaxin 1A nor 1B was found, in keeping with the neuronal restriction of these isoforms. In contrast, syntaxins 2 and 4 were readily detectable. By subcellular fractionation and estimation of protein yields, 67% of syntaxin 4 was localized to the plasma membrane, 24% to the low-density microsomes, and 9% to the high-density microsomes. Interestingly, acute insulin treatment decreased the content of syntaxin 4 in low-density microsomes and caused a corresponding gain in the plasma membrane fraction, reminiscent of the recruitment of GLUT4 glucose transporters. In contrast, there was no change in the distribution of syntaxin 2, which was mostly associated in the plasma membrane. A fraction of the intracellular syntaxin 4 was recovered with immunopurified GLUT4-containing vesicles. Moreover, anti-syntaxin 4 antibodies introduced in permeabilized 3T3-L1 adipocytes significantly reduced the insulin-dependent stimulation of glucose transport, in contrast to the introduction of irrelevant immunoglobulin G, which was without consequence. We propose that either the plasma membrane and/or the vesicular syntaxin 4 are involved in docking and/or fusion of GLUT4 vesicles at the cell surface of 3T3-L1 adipocytes.

3T3 Cells↗

PubMed1996

Characterization of SNARE protein expression in beta cell lines and pancreatic islets.

Pancreatic beta cells and cell lines were used in the present study to test the hypothesis that the molecular mechanisms controlling exocytosis from neuronal cells may be used by the beta cell to regulate insulin secretion. Using specific antisera raised against an array of synaptic proteins (SNAREs) implicated in the control of synaptic vesicle fusion and exocytosis, we have identified the expression of several SNAREs in the islet beta cell lines, beta TC6-f7 and HIT-T15, as well as in pancreatic islets. The v-SNARE vesicle-associated membrane protein (VAMP)-2 but not VAMP-1 immunoreactive proteins were detected in beta TC6-f7 and HIT-T15 cells and pancreatic islets. In these islet-derived cell lines, this 18-kDa protein comigrated with rat brain synaptic vesicle VAMP-2, which was cleaved by Tetanus toxin (TeTx). Immunofluorescence confocal microscopy and electron microscopy localized the VAMP-2 to the cytoplasmic side of insulin containing secretory granule membrane. In streptolysin O permeabilized HIT-T15 cells, TeTx inhibited Ca2+-evoked insulin release by 83 +/- 4.3%, which correlated well to the cleavage of VAMP-2. The beta cell lines were also shown to express a second vesicle (v)-SNARE, cellubrevin. The proposed neuronal target (t)-membrane SNAREs, SNAP-25, and syntaxin isoforms 1-4 were also detected by Western blotting. The beta cell 25-kDa SNAP-25 protein and syntaxin isoforms 1-3 were specifically cleaved by botulinum A and C toxins, respectively, as observed with the brain isoforms. These potential t-SNARES were localized by immunofluorescence microscopy primarily to the plasma membrane in beta cell lines as well as in islet beta cells. To determine the specific identity of the immunoreactive syntaxin-2 and -3 isoforms and to explore the possibility that these beta cells express the putative Ca2+-sensing molecule synaptotagmin III, RT-PCR was performed on the beta cell lines. These studies confirmed that betaTC6-F7 cells express syntaxin-2 isoforms, 2 and 2', but not 2'' and express syntaxin-3. They further demonstrate the expression of synaptotagmin III. DNA sequence analysis revealed that rat and mouse beta cell syntaxins 2, 2' and synaptotagmin III are highly conserved at the nucleotide and predicted amino acid levels (95-98%). The presence of VAMP-2, nSec/Munc-18, SNAP-25 and syntaxin family of proteins, along with synaptotagmin III in the islet cells and in beta cell lines provide evidence that neurons and beta cells share similar molecular mechanisms for Ca2+-regulated exocytosis. The inhibition of Ca2+-evoked insulin secretion by the proteolytic cleavage of HIT-T15 cell VAMP-2 supports the hypothesis that these proteins play an integral role in the control of insulin exocytosis.

Animals↗

PubMed1996

Targeting to intestinal M cells.

The specialised, antigen-transporting, epithelial M cells in the follicle-associated epithelium (FAE) overlying gut-associated lymphoid tissues constitute the primary target for oral delivery of vaccines. Our studies have shown that polystyrene microspheres selectively bind to, and are efficiently transcytosed by, rabbit Peyer's patch M cells in closed intestinal loops. Binding of biodegradable poly(DL-lactide-co-glycolide) microspheres to rabbit Peyer's patch FAE is an order of magnitude lower than that of polystyrene microspheres. Although poly(DL-lactide-co-glycolide) microspheres are not selectively targeted to M cells, a high proportion of those which bind to M cells are transcytosed, supporting the potential of such microspheres as vehicles for oral vaccine delivery. Comparison of the binding of polystyrene microspheres by murine FAE revealed this to be markedly less extensive than by rabbit FAE. These data demonstrate that microsphere binding by M cells depends on the surface properties of both cells and microspheres and suggest that surface modification may enhance the efficacy of microsphere delivery vehicles. One such approach is the incorporation of molecules with inherent binding specificity for M cells. Lectin-binding studies have revealed that M cells exhibit pronounced regional and species variation in glycoconjugate expression. In murine intestine, certain lectins bind selectively to M cells either in Peyer's patches or caecum, or at both sites. Selective targeting to, and transcytosis of, lectin-conjugates by M cells in ligated segments of murine intestine have also been demonstrated. While several lectins display strong selectivity for rabbit caecal M cells, none to date have been identified with specificity for rabbit or rat Peyer's patch M cells. Knowledge of human M cells is limited and no lectin has yet been identified with specificity for these cells. However, at least one lectin exhibits binding specificity for FAE in the human ileum. In the future, knowledge of the regional patterns of M cell carbohydrate expression within a species may allow lectins to be utilised to target selectively antigenic material to the mucosal immune system at specific locations.

Administration, Oral↗

PubMed1995

Sterol regulation of fatty acid synthase promoter. Coordinate feedback regulation of two major lipid pathways.

The gene encoding fatty acid synthase, the essential multi-functional enzyme of fatty acid biosynthesis, is shown to be regulated by cellular sterol levels similar to genes that encode important proteins of cholesterol metabolism. We show that expression of the endogenous FAS gene is repressed when regulatory sterols are included in the culture medium of HepG2 cells and that the FAS promoter is subject to similar regulation when fused to the luciferase reporter gene. Mutational studies demonstrate that sterol regulation is mediated by binding sites for the sterol regulatory element-binding protein (SREBP) and transcription factor Sp1, making it mechanistically similar to sterol regulation of the low density lipoprotein receptor gene. It is also demonstrated that SREBP and Sp1 synergistically activate the FAS promoter in Drosophila tissue culture cells, which lack endogenous Sp1. These experiments provide key molecular evidence that directly links the metabolism of fatty acids and cholesterol together.

Animals↗

PubMed1995

Determinants of progression to cirrhosis or fibrosis in pure alcoholic fatty liver.

"Pure" alcoholic fatty liver has been widely assumed to be "benign" with very low risk of progression to cirrhosis. Studies thus far have included either patients with coexisting recognised precursor lesions of cirrhosis or have been restricted to short-term histological follow-up. We have followed 88 patients, first seen between 1978 and 1985, with a histological diagnosis of pure alcoholic fatty liver and no evidence of fibrosis or alcoholic hepatitis, for a median of 10.5 years, to determine any factors predictive of disease progression. Of the 88, at follow-up nine had developed cirrhosis and a further seven fibrosis. Eight of nine patients with cirrhosis had continuing alcohol consumption of more than 40 units per week at follow-up; in the other patients, consumption was unknown. Independent histological predictors of progression on index biopsy were: presence of mixed macro/microvesicular fat, and presence of giant mitochondria. We can no longer regard alcoholic fatty liver as benign. In the presence of continuing high alcohol consumption the above histological features identified those at high risk (47-61%) of disease progression. Therefore, patients with these features should be counselled intensively regarding their alcohol consumption.

Adult↗

PubMed1995

A targeting signal in VAMP regulating transport to synaptic vesicles.

VAMP is a synaptic vesicle membrane protein required for fusion. Synaptic vesicle targeting was measured for mutants of an epitope-tagged form of VAMP in transfected PC12 cells. A signal within a predicted amphipathic alpha helix is essential for targeting to synaptic vesicles. Cellubrevin, a nonneural VAMP homolog, contains this signal and is also targeted to synaptic vesicles. Amino acid substitutions within the synaptic vesicle targeting signal either enhance or inhibit sorting of VAMP to synaptic vesicles, but do not affect the ability of VAMP to form complexes with syntaxin and SNAP-25.

Amino Acid Sequence↗

PubMed1995

Botulinum neurotoxin type C cleaves a single Lys-Ala bond within the carboxyl-terminal region of syntaxins.

Botulinum neurotoxin serotype C (BoNT/C) is a 150-kDa protein produced by Clostridium botulinum, which causes animal botulism. In contrast to the other botulinum neurotoxins that contain one atom of zinc, highly purified preparations of BoNT/C bind two atoms of zinc per toxin molecule. BoNT/C is a zinc-endopeptidase that cleaves syntaxin 1A at the Lys253-Ala254 and syntaxin 1B at the Lys252-Ala253 peptide bonds, only when they are inserted into a lipid bilayer. The other Lys-Ala bond present within the carboxyl-terminal region is not hydrolyzed. Syntaxin isoforms 2 and 3 are also cleaved by BoNT/C, while syntaxin 4 is resistant. These data suggest that BoNT/C recognizes a specific spatial organization of syntaxin, adopted upon membrane insertion, which brings a selected Lys-Ala peptide bond of its carboxyl-terminal region to the active site of this novel metalloproteinase.

Alanine↗

PubMed1995

Donor-acquired fat embolism causing primary organ failure after lung transplantation.

Technically successful bilateral sequential lung transplantation in a 40-year-old man was complicated by the immediate development of pulmonary edema on reperfusion of the allograft. Death resulted within 12 hours and was caused by the fat embolism syndrome confirmed on premortem open-lung biopsy. The donor had satisfied current selection criteria but had sustained a femoral and multiple rib fractures. This case highlights the potential risks of transplanting lungs from traumatic donors and the deficiencies in current methods of donor assessment.

Adult↗

PubMed1995

Intrahepatic mast cells in chronic liver diseases.

Mast cells are known to be present in human liver but their distribution and density in normal livers and in chronic liver diseases have not previously been examined. In this study, we quantified mast cell numbers and examined their distribution in percutaneous biopsy specimens from normal livers (n = 8) and in two chronic progressive liver diseases: primary biliary cirrhosis (PBC) (n = 40) and alcoholic liver disease (n = 33). We compared differences in mast cell density between these two forms of chronic liver disease because it had been suggested that mast cells may play a role in the development of liver fibrosis, particularly in patients with chronic cholestatic liver disease who frequently have increased plasma histamine levels. Mast cells were identified by immunohistochemistry using a specific monoclonal antibody (AA1) raised against mast cell tryptase after an initial study showed this to be more sensitive for the detection of mast cells than the conventional histochemical stain, toluidine blue. Our results showed that small numbers of mast cells (3.9 +/- 3.3/mm2) are present within the portal tracts and sinusoids of normal livers. In progressive chronic liver disease, increased numbers of mast cells were present, which correlated with the increasing amounts of liver fibrosis present. We found significantly more mast cells in the PBC group compared with the alcoholic group for a given amount of fibrosis. Our findings suggest that mast cells and their mediators may play a role in liver fibrogenesis.

Biopsy↗

PubMed1995

SNAREs and the specificity of transport vesicle targeting.

The fidelity of membrane trafficking is mediated by specific interactions between transport vesicles and their target membranes. SNAREs (SNAP receptors) are cytoplasmically oriented membrane proteins that form complexes implicated in transport vesicle targeting. Advances in the past year have provided insight into the fundamental mechanisms underlying the formation, regulation, and function of SNARE complexes.

Animals↗

PubMed1995

The effect of gastritis on human gastric alcohol dehydrogenase activity and ethanol metabolism.

BACKGROUND: Gastric mucosal alcohol dehydrogenase (ADH) may decrease the bioavailability of ingested ethanol. Because this enzyme is found in highest concentrations in the superficial gastric mucosa, diffuse abnormalities of this tissue could lead to a decrease in the first pass metabolism of ethanol. METHODS: Thirty-three adult subjects undergoing routine upper gastrointestinal endoscopy had gastric biopsies performed for assessment of gastric histology and the measurement of gastric ADH activity. Twenty of these subjects underwent separate oral dosing and intravenous infusion of ethanol (0.15 g/kg body weight) in order to determine the first pass metabolism, and hence bioavailability, of ethanol. RESULTS: Gastric histology was normal in 10 of the biopsies, showed chronic gastritis alone in 13 and significant glandular atrophy (i.e. atrophic gastritis) in a further 10. Gastric ADH activity in specimens with normal gastric histology was significantly higher than those with chronic gastritis (P = 0.02), and was further decreased in those specimens with significant atrophy (P < 0.00001). However, no correlation was found between gastric ADH activity and the first pass metabolism of ethanol (r = 0.09, P = 0.9). CONCLUSIONS: These results suggest that although gastric ADH activity was decreased in individuals with abnormal gastric mucosa, ethanol bioavailability was not affected by gastric ADH activity. These data support the view that gastric ADH does not play a significant role in the first pass metabolism of alcohol.

Adult↗