The hepatoprotective effects of Solanum alatum Moench. on acetaminophen-induced hepatotoxicity in mice

Solanum alatum Moench. has been shown to have a protective effect against carbon tetrachloride (CCl4)-induced liver injury. Solanum alatum treatment (100 mg/kg, p.o.) decreased the elevation of serum alanine aminotransferase (ALT; GPT) and aspartate aminotransferase (AST; GOT) induced by acetaminophen (paracetamol) (600 mg/kg, i.p.) administration. It also decreased the extent of visible necrosis in liver tissue. In addition, Solanum alatum treatment restored hepatic glutathione (GSH) depletion induced by acetaminophen (600 mg/kg, i.p.) administration. Microsomal enzyme levels such as P-450, reductase, and aniline hydroxylation enzyme were also restored to normal levels after Solanum alatum administration. The hepatoprotective mechanism may function through direct binding with acetaminophen toxic metabolites, decreasing the attraction of acetaminophen metabolites for other cellular GSH or thiol protein. Additionally, Solanum alatum treatment increased the concentration of hepatic GSH and maintained a high level activity of GSTase, which led to acceleration of the excretion of toxic acetaminophen metabolites.

Hemangiopericytoma of the pleura causing massive hemothorax

Hemangiopericytoma is an unusual soft tissue tumor. A 54-year-old man presented with sudden onset of chest pain and dyspnea for 1 day. The initial chest x-ray showed a massive left pleural effusion. A contrast-enhanced computed tomographic scan of the chest showed a homogenously enhanced mass in the intrathoracic extrapulmonary space. A tube thoracostomy was performed and hemothorax was confirmed. A posterolateral thoracotomy was performed and a tumor in the parietal pleura of the left chest wall was resected. Grossly, the resected tumor arose from the parietal pleura, and the cut surface was elastic, soft, and pale yellow. There were several cystic formations and hemorrhages. Based on histologic findings, hemangiopericytoma with lower grade malignancy was diagnosed. The patient was alive and free from tumor recurrence 1 year after surgery. Intrathoracic extrapulmonary hemangiopericytoma is extremely rare, and surgical excision is the treatment of choice. Adjuvant chemotherapy or radiotherapy is indicated because of the high risk of recurrence and potential malignancy.

Effects of word spacing on reading Chinese text from a video display terminal

This study investigated the effects of designing space between words in Chinese text, i.e., whether using a "word" instead of a "character" as a presentation unit, will facilitate the performance of reading from a video display terminal. Experimental results indicated that the main effect of word spacing significantly affected the reading time and the number of questions answered correctly. Subjects spent less time on the text with half-character word spacing or with whole-character word spacing than with conventional type (without word spacing). We also discovered that the number of questions answered correctly for stimuli with half-character spacing is significantly greater than that for stimuli with whole-character spacing, while both are smaller than for stimuli with conventional type. The additional variables, such as text difficulty and display control have significant effects as well. Our results suggested that the optimal word spacing in Chinese text should be greater than that in the traditional layout and less than a whole-character spacing. Apparently, in Chinese text, using a "word" as a presentation unit is more favorable than the traditional layouts that do not have any explicit word boundaries. The word spacing design may benefit in reading difficult or unfamiliar materials and further apply in emergency situations or in reading ambiguous sentences.

Improved cell adhesion by plasma-induced grafting of L-lactide onto polyurethane surface

Lactide-grafted polyurethanes were prepared by exposing the polyurethane films to argon plasma discharge, followed by grafting L-lactide onto the plasma-treated surface. The modified surfaces were characterized by measuring the static contact angle and by electron spectroscopy for chemical analysis (ESCA). The water contact angle of polyurethanes was decreased by L-lactide grafting, indicating hydrophilicity of the modified surface. Grafting also increased the O/C atomic ratio and C(C=O)/Ctotal percentage on the surfaces as detected by ESCA. The grafted surfaces showed enhanced attachment and growth in both 3T3 fibroblast and human umbilical vein endothelial cell culture tests. Platelet adhesion to the modified surfaces was also reduced in vitro. L-Lactide monomers grafted onto polyurethane substrates could therefore be useful in facilitating endothelial cell seeding process in small vascular graft applications.

Polyurethane blended with polylactides for improved cell adhesion and reduced platelet activation

Poly(L-lactide) (PLLA) or 50:50 poly(lactide-co-glycolide) (PLGA) was blended with a commercial polyurethane (PU), Pellethane 2103-80A, using a mutual solvent technique. After preparation by salt casting, the mechanical properties of the porous matrices were measured, and the surface element was characterized by electron spectroscopy for chemical analysis. The attachment and growth of fibroblasts as well as human umbilical vein endothelial cells on the substrates were investigated by the cell culture test. Platelet activation on different substrates was also studied. It was found that blending with these biodegradable polymers, especially PLGA. enhanced the cellular attachment and growth. This enhancement may be correlated with the higher oxygen/carbon (0/C) atomic ratio on the surface of the blends. Blending with either PLLA or PLGA was also found to decrease platelet adhesion and activation in vitro. These characteristics make PU/polylactide blends potential substrates for cardiovascular applications.

The influence of propolis ethanol extract on liver microsomal enzymes and glutathione after chronic alcohol administration

Propolis designates a series of gums, resins and balms of viscous consistency, which are gathered by honeybees from certain parts, mainly the buds and barks of plants, especially those found on coniferous trees. Bees bring propolis back to the hive, where it is modified and mixed with other substances including the bees' own wax and salivary secretions. In this study, the influences of propolis ethanol extract on chronic alcohol induced liver microsomal enzyme changes were investigated. Three grams of alcohol was added to rats' daily diet for four weeks to induce chronic alcohol liver injuries, and two different doses of propolis ethanol extract were p.o. administrated three times per day on the 28th, 29th, and 30th day. During the period of propolis administration, the ethanol diet was continued. After sacrifice, the rat livers were excised for assay of microsomal enzymes activity, glutathione (GSH) concentration, glutathione-S-transferase (GSTase) and gamma-glutamylcysteine synthetase (gamma-GCSase) activity. It was found that 30 mg/kg of propolis ethanol extract significantly prevented the elevations of total cytochrome P-450 enzymes, NADPH-dependent cytochrome C reductase, aniline hydroxylation, 7-ethoxyresorufin hydroxylation (7-ERH), 7-penthoxyresorufin hydroxylation (7-PRH), and lipid peroxidation induced by chronic ethanol administration. Additionally, propolis ethanol extract (100 mg/kg) also induced GSTase and gamma-GCSase activities and decreased glutathione levels in the liver.

The effectiveness of cyclic and continuous oral clodronate therapy on bone density and markers in osteopenic postmenopausal women

Bisphosphonates have been used effectively to treat established osteoporosis and prevent postmenopausal bone loss. However, the optimal manner of its administration-whether cyclic or continuous-has not been well established. This study investigated the efficacy of cyclic and continuous oral administration of clodronate in 54 newly identified osteopenic postmenopausal women in a randomized, double-blind, crossover fashion. The participants were randomly separated into two groups. The cyclic group (n = 29) received 800 mg twice daily of oral clodronate for 2 weeks every 3 months for the first 12 months followed by placebo for the second 12 months. The continuous group (n = 25) received placebo in the first 12 months and ingested 400 mg of clodronate once daily for the second 12 months. The urinary amino-terminal (NTXtrade mark) and carboxy-terminal (CrossLapstrade mark) cross-linked fragments of type I collagen, both markers of bone resorption, showed a marked decrease (25-50%) with both regimens during the period of active treatment. In the cyclic group, the levels of these two markers increased in the second 12 months with placebo, but did not return to the baseline completely. However, bone mineral density (BMD), determined by dual-energy X-ray absorptiometry (DXA), showed no significant change of BMD at various sites after 1 year of active treatment in both groups. Thoracic and lumbar spine X-ray showed no new vertebral fracture in either group after 2 years of treatment. With the two treatment protocols in this study, oral clodronate was effective in decreasing postmenopausal bone resorption, causing no significant changes in BMD at various sites.

The effect of epitope variation on the profile of cytotoxic T lymphocyte responses to the HIV envelope glycoprotein

To address the relationship between viral and host factors during HIV infection, we analyzed the effect of viral mutations on T cell responses in seropositive, asymptomatic HLA-A2+ individuals using four envelope (env)-specific peptides with the HLA-A*0201 binding motif. We showed that the natural sequence variation was frequent within epitopes located in the C-terminal region of the env glycoprotein and was largely responsible for a lower env-specific cytotoxic T lymphocyte (CTL) activity in the peptide-stimulated cultures. The highest CTL responses in vitro were induced with conserved epitopes D1 and 4.3 that mapped to the N-terminal region of the env glycoprotein. These peptides exhibited high binding affinity for HLA-A*0201 molecules and stimulated CD8+ T cells of relatively limited TCR Vbeta chain repertoire. Decreased CTL activities to the D1 epitope were observed in the absence of any detectable viral mutation, and were associated with lower proliferative responses and expression of the CD28 antigen. Results of this study demonstrate that the degree of sequence variation within a stimulatory epitope of the viral quasispecies, as well as proliferative potential of the effector cells, are among the factors underlying decreased CTL activity in HIV-infected patients. These experiments also provide evidence that the D1 peptide might be useful for the development of vaccines and immune-based therapy.

Air-liquid interfacial movement in models simulating airway reopening

In this model study, we simulated the initial airway reopening event in a rigid tube model. The air-liquid interface during airway reopening was assumed to be a simple axisymmetric meniscus similar to that of a two-phase flow in a rigid tube (radius R), where the applied pressures and the meniscus velocities were measured experimentally for fluids of different viscosities and surface tensions (gamma). Bulk flow contribution was deducted from the applied pressure to obtain the pressure accounting for interfacial movement (P*(int)). A semi-empirical formula for the interface was generated by dimensional analysis. The dimensionless interfacial pressure (P(int) = P*(int),R/gamma) was found to approach 2 for sufficiently small velocities, consistent with Bretherton's theoretical prediction. This formula also resembles that previously obtained in collapsible tubes simulating airways. The result suggests that the critical pressures required to reopen a collapsible airway and a non-collapsible one with the same radius are similar in magnitude (approximately 2 - 3gamma/R). However, in a collapsible airway, no significant bulk flow of lining fluids would develop while the interface proceeds, leading to a much smaller overall pressure for further reopening. Airway wall collapsibility thus could play a crucial role in maintaining proper ventilation through rapid reopening of the airway.

The effect of deletion of the V3 loop of gp120 on cytotoxic T cell responses and HIV gp120-mediated pathogenesis

New strategies for improving the efficacy of HIV vaccines are of significant importance. In this study, we analyzed the effect of deletion of the hypervariable V3 loop of gp120 on envelope (env)-specific CTL responses in PBMC of HIV-infected individuals. We showed increased CTL activities against conserved epitopes of the env glycoprotein in cultures induced with the AV3 mutant compared with those stimulated with the full-length env gene products. In contrast to the wild-type env, the AV3 mutant-expressing cells were resistant to Ab-dependent cell-mediated cytotoxicity, formed no syncytia, and neither underwent nor induced apoptosis in CD4+ cells. Thus, the AV3 mutant may redirect immune responses toward conserved epitopes of gp160, has longer expression time due to increased resistance to Ab-dependent cell-mediated cytotoxicity, and does not trigger cytopathic effects associated with apoptosis and syncytium formation. This approach may apply to other Ags of HIV, where deletions of highly variable or immunosuppressive epitopes may improve the efficacy of HIV vaccines.

Mediation of the cytotoxicity of lanostanoids and steroids of Ganoderma tsugae through apoptosis and cell cycle

A new lanostanoid ester glucoside, 3 alpha-acetoxy-5 alpha-lanosta-8,24-dien-21-oic acid ester beta-d-glucoside (1), and a known steroid, 2 beta,3 alpha,9 alpha-trihydroxy-5 alpha-ergosta-7,22-diene (2), were isolated from the fruit bodies of Ganoderma tsugae and their structures determined by spectroscopic methods. To study the cytotoxicity of 1 and 2, the changes of DNA content in human hepatocytes (Hep 3B) were studied. A sub-G1 cell stage was drastically increased after 24-h incubation with 1 (24 micrograms/mL). Compound 2 (100 micrograms/mL) inhibited the cell cycle progression of Hep 3B cells at the G2/M phase with an IC50 value of about 87.1 micrograms/mL. These results indicate that 1 causes cell death by apoptosis and 2 may possess the activity of cell cycle inhibition.

The hepatoprotective and therapeutic effects of propolis ethanol extract on chronic alcohol-induced liver injuries

Propolis designates a mixture of gums, resins and balms, of viscous consistency, which are gathered on certain parts (buds and bark, mainly) of vegetables (especially coniferous trees) by honeybees. They bring this back to the hive, where it is modified and mixed with other substances (essentially their own wax and salivary secretions). In this study, the hepatoprotective and therapeutic effects of propolis ethanol extract on chronic alcohol-induced liver injuries were investigated in rats. 3.125 ml of 99.5% alcohol was added to animal's daily diet for four weeks to induce chronic alcohol liver injuries. After sacrifice, serum transaminases (GOT, GPT), triacylglyceride and hepatic triacylglyceride (HTG) concentration were assayed to observe liver injuries induced by chronic alcohol abuse. In addition, the phenomenon of alcohol induced fatty liver were also observed by histopathological changes. Different doses of propolis ethanol extract were p.o. administered three times per day for three days, after four weeks' alcohol administration. It was found that 10 mg/kg of propolis ethanol extract significantly decreased the elevations of serum GOT, GPT, TG and HTG. In histopathological examination, 30 mg/kg of propolis ethanol extract also remarkably decreased the hepatocellular fatty degeneration, apparent as vacuolization, induced by chronic alcohol abuse.

Water Resource Protection in Taiwan: An Evaluation of the Taipei Water Management Commission

/ This study evaluates the institutional capacity and performance of the Taipei Water Management Commission. The commission, which manages the Taipei Water Special Area-one of 95 such areas in Taiwan and the only one managed by a supervisory agency-has established a record of water conservation that suggests its utility as a model for managing other protected water resources areas in Taiwan. However, its present institutional structure limits its ability deliver on its mandate. The study identifies a number of problems related to the commission's current institutional structure that need to be addressed if the commission is to serve as a viable model for managing other protected water resource areas in Taiwan.KEY WORDS: Water resources management; Commissions; Institutional capacity; Taiwan

Age differences in remote pointing performance

The purpose of this study was to investigate age differences in remote pointing movements. The subjects were recruited from three age groups (ages 18-22 yr., 40-50 yr., and 60-70 yr., with 9 men and 9 women in each group). They were required to perform cursor-positioning tasks using a remote pointing device, in which the dependent measures were the time taken to reposition the cursor and the accuracy of subjects' movement trajectories. The movement time was further separated into two components, First Submovement duration and Adjustment Submovement duration. Analysis indicated that age groups showed reduced performance on remote pointing. Moreover, remote positioning movement for the young-adult group was mostly completed in their First Submovement phase, while the elderly subjects spent most of their movement time on the Adjustment Submovement phase. These results support the proposition that different age groups exhibit different kinds of movement patterns.

Human liver CYP2B6-catalyzed hydroxylation of RP 73401

RP 73401 is a potent inhibitor of cyclic nucleotide phosphodiesterase type IV. RP 73401 is metabolized by human liver microsomes almost exclusively by transhydroxylation of the cyclopentyl group to RPR 113406. Liquid chromatography/mass spectrometry/mass spectrometry analysis of plasma from patients given RP 73401 also revealed a molecular ion and fragmentation consistent with RPR 113406. Thus, the objective was to determine the oxidative enzyme(s) responsible for RP 73401 hydroxylation. Kinetic constants of RP 113406 formation ranged from 8 to 26 MM and 0.83 to 5.99 nmol/min/mg protein for K(m) and V(max), respectively (n = 3). Enzyme activity varied 23-fold among 15 human liver microsome samples and correlated with CYP2A6-catalyzed coumarin hydroxylase (r2 = 0.85, P < .01) and CYP2B6-catalyzed 7-ethoxytrifluoromethylcoumarin O-deethylase (r2 = 0.82, P < .01) activities. Chemical inhibition studies showed a 63% decrease in RP 73401 hydroxylation by 500 microM orphenadrine. Coumarin (10 microM), however, did not inhibit RP 73401 hydroxylation. Also, anti-CYP2B1 IgG produced 85% inhibition of RP 73401 hydroxylation, but only a negligible decline in coumarin hydroxylase activity. Of the 10 expressed P450 forms studied, only CYP2B6 catalyzed RP 73401 hydroxylation. Finally, expressed CYP2B6 showed a high affinity (K(m) = 22.5 microM) for RP 73401 hydroxylation, similar to the human liver microsome studies.

The effects of ursodeoxycholic acid in patients with severe obstructive jaundice after drainage procedure

BACKGROUND

The aim of this study is to evaluate the therapeutic effect of ursodeoxycholic acid (UDCA) for patients with severe obstructive jaundice after drainage procedure.

METHODS

From September 1993 to December 1994, patients admitted with severe obstructive jaundice (serum bilirubin > 15 mg/dl) and successful drainage were enrolled into our study. They were randomly divided into two groups to receive UDCA 600 mg per day (UDCA group) or a placebo (placebo group) until operation or discharge. Bile drainage amount, clinical symptoms and signs and adverse effects of drugs were recorded daily. Biochemical tests, including albumin, total bilirubin, cholesterol, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, gamma-glutamyl transpeptidase and prothrombin time, were checked first, on the third and seventh days, and then two weeks after drainage.

RESULTS

Thirty-eight patients (M/F = 36/ 2, mean age 66.6 +/- 6.4 years) completed the study, 18 in the UDCA group and 20 in the placebo group. There were no differences in age, sex, causes of obstructive jaundice or methods of drainage procedure between the UDCA and placebo groups. Improvement in biochemical test results were noted in both groups. However, bile drainage amount and changes in liver biochemical test, especially the decrement of serum bilirubin, were not significantly different between both groups.

CONCLUSIONS

UDCA seemed not to benefit patients with severe obstructive jaundice after successful drainage.

Novel and frequent mutations of hepatitis B virus coincide with a major histocompatibility complex class I-restricted T-cell epitope of the surface antigen

We examined the full-length hepatitis B virus (HBV) envelope (surface antigen or HBV small surface antigen [HBsAg]) sequences of 12 different liver samples from 10 different hepatoma-containing chronic carriers. Surprisingly, novel and frequent mutations occurred predominantly at amino acids 40 and 47 of HBsAg, in addition to within a known protective B-cell epitope (so-called group a determinant of HBsAg 124-148). Approximately 58% of chronic carriers contain mutations at the group a determinant. The mutation frequency at the hotspot codons 40 and 47 is approximately 83%, 1 order of magnitude higher than at the known polymorphic sites of subtype-specific determinants at codons 122 and 160, which is approximately 4%. This new mutational domain is found to coincide with a major histocompatibility complex class I-restricted T-cell epitope. The potential biological significance of this novel mutation in the immunopathogenesis of HBV chronic carriers is discussed.

Vitamin D stores of urban women in Taipei: effect on bone density and bone turnover, and seasonal variation

This study was performed to survey the vitamin D nutritional status of urban Chinese women, and to define its role in determining bone metabolic rate and bone mineral density (BMD). We measured serum 25-hydroxyvitamin D (25-OHD), the major storage form of vitamin D, and BMD, at the spine, hip, and total body skeleton, of 262 healthy Chinese women aged from 40 to 72 years, residing in Taipei city. Bone turnover markers, including serum osteocalcin, bone alkaline phosphatase isozyme, and C-terminal propeptide of type I procollagen, and a urinary bone resorption marker, N-terminal crosslinked fragment of type I collagen, were also measured. We found generally adequate vitamin D nutritional stores. The mean concentration of serum 25-OHD was 30.7 (SD = 8.2) ng/mL for all 262 subjects and there were no significant age-related changes. Those who had serum sampled during the summer showed higher serum 25-OHD levels (N = 138; mean +/- SD: 32.7 +/- 7.6 ng/mL) than those who had serum sampled during winter (N = 124; mean +/- SD: 28.5 +/- 8.3 ng/mL; Student's t-test, p < 0.001), but these two groups showed similar BMD and bone marker values. Those with serum 25-OHD concentration in the lowest or highest tertile did not show different BMD or bone marker values than those in the other tertiles. Multiple regression demonstrated no correlation between 25-OHD and any bone marker or BMD at any site. Thus, in this free-living urban Chinese population, in a subtropical region, we could not demonstrate a role of vitamin D stores in determining bone turnover rate or BMD in women aged 40-70 years.

Solamargine purified from Solanum incanum Chinese herb triggers gene expression of human TNFR I which may lead to cell apoptosis

Solamargine possessed a potent cytotoxicity to human hepatocyte (Hep3B) and normal skin fibroblast. The inhibition curves of solamargine to the both cells were essentially overlapped, suggesting a parallel effect for the cell death. To define mechanism of cytotoxicity of solamargine, the changes of morphology and DNA content in cells were studied. A sub-G1 cell stage was drastically increased after 3-h incubation with solamargine. The results evidence that solamargine arises cell death by apoptosis. In addition, the gene expression of TNFR I were up-regulated within 30 min of solamargine treatment. Since TNF Receptor I has been involved in apoptosis, the overexpression of TNF receptor I may be related with the mechanism of cytotoxicity of solamargine. This communication is the first report that a component of Chinese herbs triggers gene expression of human TNFR I which may lead to cell apoptosis.

Sexual differences in bone markers and bone mineral density of normal Chinese

We measured bone mineral density (BMD) at lumbar (L2-L4) vertebrae and proximal femurs of 385 healthy Chinese women aged 40-70 years and 156 healthy Chinese men aged 20-85, and four markers-bone alkaline phosphatase isozyme (BAP), procollagen-I C terminal propeptide (PICP), osteocalcin (BGP) in serum, and a bone resorption marker, urinary cross-linked N-telopeptide of type I collagen (NTX), of these subjects. The results indicate that in postmenopausal women, levels of all the markers increased with age. In men, serum BAP, PICP, and urinary NTX decreased significantly, and serum BGP decreased with borderline significance (P = 0.08). With increasing age, bone density decreased at both sites in postmenopausal women and at the proximal femur in men. The lumbar bone density showed no significant age-related changes in men. In premenopausal women, BMD at either site showed no significant change with increasing age. Despite the different trends between men and women of age-related changes in BMD and bone markers, bone density of both proximal femur and spine in both sexes correlated inversely with levels of the bone markers in a manner independent of age or body weight. The meaning of opposite age effects on bone markers in men and women needs further investigation. In addition, higher bone marker levels, implying faster bone turnover rate, are associated with lower BMD in both sexes.

Bone mineral density and bone markers in relation to vitamin D receptor gene polymorphisms in Chinese men and women

Whether vitamin D receptor gene (VDRG) polymorphism can be used as a predictor for bone turnover rate or bone mass remains controversial. Its role within various ethnic populations are also unsettled. We examined VDRG polymorphism using restrictive enzymes Bsm-I, Apa-I, and Taq-I in 155 men aged 22-88 and 113 premenopausal women aged 40-53. The bone mineral density (BMD) of the vertebrae (L2-4), proximal femur, and total body bone mineral content (tb-BMC) (women only), as well as urinary N-terminal crosslinked fragment of type I collagen (NTX), serum osteocalcin, bone isozyme of alkaline phosphatase, and caboxyterminal propeptide of type I procollagen levels were measured. Chinese men and women exhibited a low prevalence for B (absence of Bsm-I restriction site) phenotypes than white and Japanese. Within the tested samples there were 0.4% BB homozygotes, 6.7% Bb heterozygotes, and 93% bb homozygotes. The distributions of Apa-I polymorphism (9.0% AA, 42.5% Aa, and 48.5% aa) also differed from those reported for the white populations. Most of the Chinese men and women were TT homozygous (96.6%). A comparison of actual values and values adjusted for age and weight of tb-BMC and BMD at the lumbar spine, Trochanter, Ward's triangle, and femoral neck showed no significant difference among three subgroups in each of the three sets of polymorphism. Furthermore, the actual values and adjusted values (adjusted for age) of the four bone markers, respectively, showed no significant differences. We conclude that given the very low prevalence of the suspected high risk genotypes (B, A, and t), and the lack of difference among the polymorphic subgroups, VDRG polymorphism may not be an important determinant of the bone turnover rate and bone mass of Chinese men and women.

Role of viscoelasticity in the tube model of airway reopening. II. Non-Newtonian gels and airway simulation

The influence of viscoelastic gels as lining fluids on the pressure-velocity relationships in an airway tube model (Gaver et al. J. Appl. Physiol. 69: 74-85, 1990) was examined. A flow instability was observed due to the occurrence of a sol-gel transition in the viscoelastic properties under flow conditions. We further report measurements of the viscoelastic properties of airway secretions. Airway secretions are gels under small strains and have a yield stress of 4-7 dyn/cm2. Secretions from the pharyngeal airway show lower elasticity than secretions from the trachea. The airway reopening process is simulated using a Weibel lung geometry by incorporating the constitutive equations from the model gel studies and utilizing the rheological data on airway secretions. In these simulations, a "popping-open" phenomenon arises from a flow instability in airway generations 8-14 when the rheological properties of the lining fluids are assumed to be similar to those of pharyngeal secretions. On the basis of these studies, the elasticity of airway secretions plays an important role in airway reopening.