Natural Underwater Bioadhesive Offering Cohesion Modulation via Hydrogen Bond Disruptor: A Highly Injectable and in Vivo Stable Remedy for Gastric Ulcer Resolution

Injectable bioadhesives are attractive for managing gastric ulcers through minimally invasive procedures. However, the formidable challenge is to develop bioadhesives that exhibit high injectability, rapidly adhere to lesion tissues with fast gelation, provide reliable protection in the harsh gastric environment, and simultaneously ensure stringent standards of biocompatibility. Here, a natural bioadhesive with tunable cohesion is developed based on the facile and controllable gelation between silk fibroin and tannic acid. By incorporating a hydrogen bond disruptor (urea or guanidine hydrochloride), the inherent network within the bioadhesive is disturbed, inducing a transition to a fluidic state for smooth injection (injection force <5 N). Upon injection, the fluidic bioadhesive thoroughly wets tissues, while the rapid diffusion of the disruptor triggers instantaneous in situ gelation. This orchestrated process fosters the formed bioadhesive with durable wet tissue affinity and mechanical properties that harmonize with gastric tissues, thereby bestowing long-lasting protection for ulcer healing, as evidenced through in vitro and in vivo verification. Moreover, it can be conveniently stored (≥3 m) postdehydration. This work presents a promising strategy for designing highly injectable bioadhesives utilizing natural feedstocks, avoiding any safety risks associated with synthetic materials or nonphysiological gelation conditions, and offering the potential for minimally invasive application.

Analysis of risk factors associated with endoscopic retrograde cholangiopancreatography for patients with liver cirrhosis: a multicenter, retrospective, clinical study

BACKGROUND

Endoscopic retrograde cholangiopancreatography (ERCP) is the endoscopic modality of choice for the treatment of biliary and pancreatic diseases. However, patients with cirrhosis, particularly those with decompensated cirrhosis, are believed to be at increased risk for complications associated with ERCP. There is a paucity of literature describing the outcomes of ERCP for patients with cirrhosis. This study aimed to investigate the outcomes of ERCP for cirrhosis patients, especially adverse events, and evaluated its safety and efficacy.

METHODS

We performed a multicenter, retrospective study of all patients at Beijing Friendship Hospital affiliated to Capital Medical University, Xijing Hospital affiliated to Air Force Military Medical University, Beijing Youan Hospital affiliated to Capital Medical University, and the Fifth Medical Center of the People's Liberation Army General Hospital from June 2003 to August 2019. The adverse events of inpatient ERCP for patients with ( n  = 182) and without liver cirrhosis (controls; n  = 385) were compared.

RESULTS

A total of 567 patients underwent ERCP between January 2003 and December 2019 were enrolled in this study. Compared to patients without cirrhosis, patients with cirrhosis were at higher risk for postoperative complications (odds ratio [OR], 4.172; 95% confidence interval [CI], 1.232-7.031; P  < 0.001) such as postoperative pancreatitis (OR, 2.026; 95% CI, 1.002-4.378; P  = 0.001) and cholangitis (OR, 3.903; 95% CI, 1.001-10.038; P  = 0.036). The main indications for ERCP for patients with cirrhosis in this study included choledocholithiasis (101 cases; 55.5%), benign bile duct strictures (46 cases; 25.3%), and malignant bile duct strictures (28 cases; 15.4%). Among them, 23 patients (12.6%) underwent balloon dilation and 79 patients (43.4%) underwent sphincterotomy. Of the patients with cirrhosis, delayed bleeding occurred in ten patients (5.5%), postoperative pancreatitis occurred in 80 patients (44.0%), and postoperative cholangitis occurred in 25 patients (13.7%). An additional multivariate analysis showed that the total bilirubin (TBIL) level (OR, 4.58; 95% CI, 2.37-6.70) and Child-Pugh score of C (OR, 3.11; 95% CI, 1.04-5.37) were risk factors for postoperative complications in patients with cirrhosis.

CONCLUSIONS

Compared with the general population of patients undergoing ERCP, patients with cirrhosis were more prone to postoperative pancreatitis and cholangitis. TBIL levels and Child-Pugh scores were risk factors for postoperative complications in patients with cirrhosis.

Efficacy of single- versus split-dose polyethylene glycol electrolyte solution for morning colonoscopy: A randomized controlled study

BACKGROUND

Split-dose (SPD) regimen has been proved more effective than a single-dose (SID) regimen for various drug preparations; however, limited data have focused on morning colonoscopy. We implemented this study to compare the bowel cleanliness and tolerability of a same-day SID versus SPD 2 L polyethylene glycol electrolyte solution (PEG) for morning colonoscopy.

METHODS

Patients undergoing morning colonoscopy were randomized into two groups, SID or SPD. In the SID group, patients had to complete 2 L PEG between 4 and 6 am on the day of colonoscopy. In the SPD group, patients had to complete 1 L PEG between 8 and 9 pm on the day before followed by another 1 L PEG between 5 and 6 am on the day of colonoscopy. Colonoscopy was performed between 8 and 12 am under anesthesia. Investigators and endoscopists were blinded to the allocation. The primary end point was the effectiveness of bowel cleansing according to the Boston Bowel Preparation Scale (BBPS). The secondary outcomes were polyp detection rate, compliance, tolerability, and patient satisfaction.

RESULTS

Overall, there were 147 and 148 patients in the SID and SPD group, respectively. The SPD group had a better quality of bowel preparation than the SID group with a total BBPS score of 7.25 ± 1.53 versus 6.71 ± 1.65 (P = 0.005). No difference in the polyp detection rate was noted, although more polyps were detected in the SPD group. More patients felt acceptable with the bowel preparation regimen in the SPD group compared to the SID group (76% vs. 65%, P = 0.03). The adverse events were more commonly observed in the SID group, presented as nausea and vomiting.

CONCLUSION

For morning colonoscopy, split-dose 2 L PEG is superior to single-dose 2 L PEG by improved bowel preparation, better tolerability, and patient satisfaction.

High-intensity focused ultrasound and laparoscopic myomectomy in the treatment of uterine fibroids: a comparative study

OBJECTIVE

To compare the clinical efficacies of high-intensity focused ultrasound (HIFU) and laparoscopic myomectomy (LM) in the treatment of uterine fibroids and their effects on patients' quality of life.

DESIGN

A non-randomised control study.

SETTING

Gynaecological department in a university teaching hospital.

POPULATION

Patients with uterine fibroids.

METHODS

From November 2014 to November 2015, 166 patients with uterine fibroids were enrolled and underwent HIFU (n = 99) and LM (n = 67) surgeries, respectively. Clinical efficacy, postoperative complications and quality of life after treatment were evaluated using the SF-36 Scale to compare the differences in each variable at the 1-year follow up.

MAIN OUTCOMES MEASURES

Differences in efficacy, safety and quality of life between the patients treated with HIFU and LM.

RESULTS

The 12-month follow-up results showed that the HIFU group had a total effective rate of 99%; only one patient underwent alternative treatment due to non-apparent tumour shrinkage. All patients in the LM group showed complete tumour disappearance. Of these patients, 52 showed significant clinical improvement, 15 with partial clinical improvement, a total effective rate of 98%. There was no significant difference in effectivity rate between the two groups (P > 0.05). Both treatments effectively improved patients' quality of life. Compared with the LM group, patients in the HIFU group experienced no blood loss, a shorter hospital stay and fewer adverse effects and complications, the difference being statistically significant (P < 0.05).

CONCLUSIONS

High-intensity focused ultrasound can be as efficacious as LM therapy and effectively improve patients' quality of life in the treatment of uterine fibroids, with fewer adverse effects and complications, shorter hospital stays, and quicker postoperative recovery compared with LM therapy.

TWEETABLE ABSTRACT

Patients with uterine fibroids can be effectively treated with both HIFU and myomectomy.

One-step approach for the synthesis of CoFe2O4@rGO core-shell nanocomposites as efficient adsorbent for removal of organic pollutants

CoFe₂O₄-reduced graphene oxide nanocomposites (CFG) have been successfully synthesized via one-step solvothermal method. The prepared CFG are characterized by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, field emission scanning electron microscopy (FESEM), vibrating sample magnetometer and so on. The FESEM results show that CFG have uniform core-shell structure with an average diameter of about 75 nm and the thickness of the outer graphene shell is about 15-20 nm. The mass ratio of CoFe₂O₄ to graphene oxide is a key factor affecting the formation of core-shell hybrids. CFG display much higher adsorption capacity for anionic dyes than cationic dyes owing to the favorable electrostatic interaction. The adsorption capacity for methyl orange is observed as high as 263 mg g^-1 at 298 K, and the adsorption isotherms follow the Langmuir model. Furthermore, the specific saturation magnetization (Ms) of CFG is 32.8 emu g^-1, and the as-synthesized nanocomposites can be easily separated by external magnetic field after adsorption. The results suggest that CFG have great potential for the practical industrial wastewater treatment.

The directional sensitivity of the acoustic radiation force to particle diameter

When viscous corrections to the inviscid acoustic radiation force theory are implemented and applied to a standing wave field, the direction of the acoustic radiation force on particles varies from theory to theory. Specifically, some theories predict that the direction of the force depends on the particle diameter, while others reveal that the direction of the force is independent of particle diameter. The present study is an experimental investigation of the direction of the acoustic radiation force which suggests that particle diameter does affect the direction. Experiments were conducted in air using an ultrasonic standing wave field with a nominal frequency of 30 kHz. Smoke particles and fine water droplets having a range of diameters were flowed into the region of a standing wave field. The direction of the acoustic radiation force was determined by observing whether the particles accumulated in the nodes or the anti-nodes of the standing wave. Results show a change in the direction of the acoustic radiation force at a particle diameter of 0.3±0.1 μm, which corresponds to a particle diameter to acoustic-boundary-layer thickness ratio of 0.023±0.008.

[Primary intestinal non-Hodgkin's lymphoma: a retrospective study of 85 cases]

OBJECTIVE

To review the clinical characteristics and treatment outcomes of primary intestinal non-Hodgkin's lymphomas (PINHL) and analyze the differences between T-cell and B-cell lymphomas.

METHODS

The characteristics of PINHL patients treated in our hospital between January 2003 and December 2010 were reviewed for their clinical manifestations, diagnosis, endoscopic findings, treatments and outcomes.

RESULTS

Eighty-five cases of PINHL meeting the Dawson's criteria were identified. The median age of the patients at the time of diagnosis was 52 years and the male: female ratio was 3.05:1; 58 cases (68.2%) had B-lineage and 27 cases (31.8%) had T-cell lineage lymphomas. Compared to those with B-cell lymphoma, patients with T-cell lymphomas showed a younger age of disease onset (32 vs 56 years, P<0.01) and presented with a greater incidence of such symptoms as fever, hematochezia, diarrhea and night sweats (P<0.05); T-cell lymphoma showed more multifocal and ulcerative/ulcero-infiltrative lesions under endoscope with a longer diagnosis time (4 vs 2 months, P<0.01) and a greater likeliness of misdiagnosis (16/27 vs 12/58, P<0.01) and poor prognosis. Extranodal NK/T-cell lymphoma was the most common type of T-cell lymphomas.

CONCLUSION

In our cases, T-cell lymphoma appeared to be more common than B-cell lymphoma with a younger onset age, more difficult diagnosis, a greater likeliness of misdiagnosis, poorer prognosis and more extranodal NK/T-cell lymphoma.

Field studies on 32P movement and P leaching from flooded paddy soils in the region of Taihu Lake, China

Field experiments were done in two sites, Yixing and Changshu, Jiangsu province, China, to study P movement and leaching in flooded paddy soils. P movement in soil was investigated by using the KH2 32PO4 tracker method, and the amount of P leached from the soil layer in different depths was estimated by measuring P concentrations in the soil solution and saturated hydraulic conductivities in field. Determination was done about one month after P application. There was 46% and 42% of total 32P retained in the 0-5cm layer of soil in the Yixing site and in the Changshu site respectively. The 32P retained in the 25-30 cm layer was only about 1-2% of the total 32P added. Furthermore, 8.01% of 32P in the soil of Yixing site and 16.8% of 32P in the soil of Changshu site was lost from the layer 0-30 cm soil. The seasonal amounts of P leached from the top soil layer and from bottom layer are about 4.5-5.8% and 1.6-2.1% of the total P application, respectively. Changes of total P concentrations in soil solutions during rice growth showed that the fertilizer P applied before flooding of the paddy fields suffered a flash leaching loss and a slow leaching loss. We concluded that the fertilizer P could quickly move in the flooded paddy rice field and parts of it can enter into surface water and ground water. Unless the P application is well managed the risk of P loss and consequently environmental pollution exist.

Content and distribution of forms of organic N in soil and particle size fractions after long-term fertilization

Most of the N in surface soils occurs in organic forms, and when mineralized it plays a key role in soil fertility and plant nutrition. Our objective was to study the effect of long-term applications of organic manure on the content and distribution of forms of organic N in bulk soil and soil particle size fractions to characterize the inherent soil nitrogen fertility. Five treatments were as follows: (1) CK (no fertilizer and no manure added), (2) mineral fertilizer only, (3) straw + NPK, (4) green manure + NPK and (5) pig manure + NPK. Soil particle size fractions (0-2, 2-10, 10-50 and 50-100 microm) were isolated without chemical pretreatment by ultrasonic dispersion in water followed by sedimentation. The content of total N and forms of organic N in the bulk soil increased after long-term fertilization, and the effect varied with fertilizer type. The plot treated with only mineral fertilizer gave the highest NH3-N and the lowest amino sugar-N content in all treatments. The highest content of amino sugar-N and amino acid-N was found in the treatment of pig manure + NPK. The content (g kg(-1) fraction) of hydrolysable N within size fractions was in the order 0-2 > 2-10 > 50-100 > 10-50 microm, but the contribution of different size fraction to hydrolysable N decreased in the sequence 10-50 > 0-2 > 2-10 > 50-100 microm. Most of the applied mineral fertilizer N that remained in soils was distributed in the particle size fraction < 2 microm while most of the remaining N from manure applied with NPK was transferred into amino sugar-N in each size fraction, and amino acid-N in the size fractions > 2 microm during the process of humification.

Mechanisms of nitrite accumulation occurring in soilnitrification

Because low concentration of nitrite could be toxic to biological systems and high amounts of nitrite have been observed in a river of northern China since 1990, nitrite from agricultural soil sources should be investigated. In this paper, effects of levels of ammonium-N (NH4+-N), soil pH and nitrification inhibitors on NO2- accumulation, and duration of nitrite in soils were studied. Application of 11.2 mg of nitrapyrin kg(-1) soil or 11.2 mg of sodium azide kg(-1) soil dramatically suppressed nitrite occurrence. Within all incubation times and at all levels of ammonium-N input, we did not detect any measurable NO2-N accumulation in samples of Yellow-brown earth (pH 5.67), but observed huge accumulation in the 2 alkaline soils, Fluvo-aquic loam (pH 7.89) and Fluvo-aquic sand (pH 8.20). The concentrations of nitrite in both alkaline soils were related to ammonium-N levels. The effect of pH on nitrite accumulation was demonstrated by using slurries of Fluvo-aquic sand under continuous aeration and buffers of different pH. Data showed that nitrite concentration increased with the elevated pH, yet that ammonia oxidizers from the original soil (pH 8.2) could adapt to the new medium of low pH (pH 5.35). Dynamic changes of nitrite in soils amended with different rates of nitrite-N were also measured in 6 days. Thereby, we concluded that nitrite was unstable in acid soils, but durable in alkaline soils. The authors suggested that NO2- accumulation in field soils and its subsequent environmental impact should receive more attention.

[Three-dimensional surface reconstruction of spiral CT for teeth and clinical use in examining impacted teeth of jaws]

OBJECTIVE

To establish a new technique for three-dimensional surface reconstruction of teeth (dental surface reconstruction), and apply it to investigate impacted teeth in bone before operation.

METHODS

On the basis of three-dimensional surface reconstruction of teeth and jaws, the dental surface reconstruction is obtained with the technique of shaded surface display (SSD), making transparent bone around. This technique is applied to investigate 9 cases of supernumerary and impacted teeth.

RESULTS

Dental surface reconstruction image can present the dental surface image including crown, root, neck and root bifurcation in three-dimensional way, without presenting the image of other tissue around. In 4 cases, the abnormal configuration, labial or palatal location, and relation with dentition in anterior maxilla of 5 supernumerary were shown. In 1 case, the shape, location, eruption orientation and the angle of orthodontic distraction of 1 impacted permanent canine were displayed. In 3 cases, the shape, location, and extraction resistance of 6 impacted wisdom teeth were revealed. In 1 case, the configuration, distance to adjacent molar of 1 impacted wisdom tooth, which is a transposition tooth in maxillary sinus, were also demonstrated.

CONCLUSION

The dental surface reconstruction is a new technique to display three-dimensional surface configuration of teeth. This technique can be applied to examine impacted and supernumerary teeth before surgical and orthodontic treatment.

[Applied anatomy of insular skin flap of nasolabial groove with retrograde superior labial artery]

In order to study the feasibiliy of the insular skin flap of the nasolabial groove with the retrograde superior labial artery, 8 adult cadavers were dissected and the relation between the superior labial artery and the skin of nasolabial groove was observed. The result revealed that superior labial artery was one of the branches of the facial artery and could be found in every cadaver. The diameter of the artery was 0.8 +/- 0.1 mm and the length was about 90 mm. The left and right facial arteries were connected with each other in the mid-line in the formation of the arcuate artery. The arcuate artery lay within the submucous tissue beyond the vermilion border about 6 mm. The concomitant veins were constant. If the facial artery being sectioned was beyond its initial site of superior labial artery, the skin of nasolabial groove on the same side could receive blood supply from contralateral supperior labial artery. The conclusion was that the insular skin flap of the nasolabial groove with the retrograde superior labial artery could be used in patients, because it had support from anatomical research.

The microvasculature of human infant oral mucosa using vascular corrosion casts and india ink injection. II. Palate and lip

The microvasculature of human hard and soft palate and lip originating from four infant males and six females, aged 6 months to 2 years was studied by scanning electron microscopy of vascular corrosion casts and light microscopy of India ink injected specimens. The capillary loops of the hard palate mucosa and vermilion border of the lips were found to be tall, numerous and consisted of primary, secondary and tertiary loops. Those of the soft palatal and labial mucosa were short, few in number and demonstrated a simple hair-pin shape originating directly from the subpapillary vascular network. It was concluded that the configuration of capillary loops is not only determined by the shape of the connective tissue papillae in the lamina propria but also influenced by the functional demands characteristic of the different areas of the oral mucosa.

The microvasculature of human oral mucosa using vascular corrosion casts and India ink injection. I. Tongue papillae

The microvasculature of human tongue papillae originating from 9 males and 6 females, aged 0.5 to 2 years was studied by scanning electron microscopy (SEM) of vascular corrosion casts and by light microscopy (LM) of India ink injected specimens. All papillae showed a microvasculature characterized by primary, secondary and tertiary capillary loops. In the filiform papillae the loops were generally arranged in a corolla-like pattern with the tertiary loops demonstrating a hair-pin shape. The fungiform papillae showed basically a similar architectural pattern although the loops were somewhat more compact and complex in structure. A small, shallow depression of the tertiary loops at the top of these papillae was found to be occupied by a prominent rete ridge of the surface epithelium. There was a gradual transition from filiform to foliate papillae, the latter appearing as rows of coalesced filiform papillae. The circumvallate papillae easily identified by the surrounding furrow showed a rather complex and compact pattern of capillary loops of which typical hair-pin shaped tertiary loops dominated the periphery of the papilla. Small grooves or depressions in the vascular network were found to be occupied by rete ridges of the overlying mucosal epithelium.

[Observations on microvasculature of the periosteum of infant mandibular ramus by scanning electron microscope]

In this paper, a vascular casting method using methylmethacrylate was adopted. Satisfactory samples were obtained and electron microscope observations were carried out on periosteum microvasculature of infant mandibular ramus. There were significant differences in the density and arrangement of periosteal microvascular in various regions. In muscular attached region, the blood vessels showed a high density and bundle-like arrangement parallel with the direction of muscular fibers. In nonmuscular attached region, the blood vessels showed a marked low density and an irregular net-like arrangement. Between muscular bundles small arteries into periosteum were seen. Around the mandibular foramen the vessels of the periosteum formed a high density region. The clinical application of the above mentioned results were discussed.

A mutation in the catalytic subunit of protein kinase A prevents myristylation but does not inhibit biological activity

The catalytic of subunit of cAMP-dependent protein kinase is acylated at its NH2 terminus with myristic acid. This type of modification is thought to mediate the association of proteins with lipid bilayers, yet the catalytic subunit shows no preferential binding with membranes. We investigated the role of C subunit myristylation using a cDNA expression vector in which the acylated NH2-terminal Gly was mutagenized to Ala. Protein synthesized in NIH 3T3 cells from this modified gene did not incorporate [3H]myristate. However, the kinase activity of this altered C subunit on a synthetic substrate was not diminished, nor was its ability to form holoenzyme with regulatory subunit. Non-myristylated C subunit also regulated several biological processes occurring in specific subcellular compartments; mutant C subunit stimulated dramatic cell shape changes controlled by the cytoskeleton, restored steroidogenesis in the mitochondria of defective adrenocortical cells, and effectively induced the transcription of genes in the nucleus. These results suggest that myristylation is nonessential for C subunit conformation and enzyme activation, and is not required for C subunit interaction with other proteins in regions where C is thought to localize upon activation. The purpose for NH2-terminal myristylation of this important signal-transducing enzyme remains an enigma.

Two independent growth factor-generated signals regulate c-fos and c-myc mRNA levels in Swiss 3T3 cells

Polypeptide growth factors that stimulate cell proliferation bind to cell surface receptors and activate intracellular signal transduction pathways. One major signalling pathway, initiated by phosphatidylinositol (PI) turnover, involves activation of protein kinase C. Some polypeptide growth factors, including mitogens that activate protein kinase C, induce a rapid increase in expression of the proto-oncogenes, c-myc and c-fos. In order to characterize the signal transduction pathways responsible for proto-oncogene activation, we treated Swiss 3T3 cells with the tumor promoter phorbol dibutyrate to generate cells deficient in protein kinase C. These cells were then stimulated with platelet extract, bombesin, or epidermal growth factor (EGF) and the levels of c-myc and c-fos mRNA were determined. Platelet extract or bombesin, which stimulate PI turnover, were substantially weaker inducers of c-myc and c-fos mRNA levels in the protein kinase C-depleted cells, although some variability with platelet extract was noted. EGF, which does not stimulate PI turnover in several cell systems, was by contrast a potent inducer of both proto-oncogenes whether or not the cells were deficient in protein kinase C. Pretreatment of cells with phorbol dibutyrate caused little or no change in the basal levels of c-myc or c-fos mRNA, but led to a small but significant increase in basal levels of ornithine decarboxylase mRNA. These results demonstrate that EGF and growth factors that activate PI turnover induce expression of the c-myc and c-fos proto-oncogenes through different pathways.

Induction of c-fos and c-myc mRNA by epidermal growth factor or calcium ionophore is cAMP dependent

Phorbol esters activate protein kinase C and induce expression of the c-fos and c-myc protooncogenes in density-arrested BALB/c 3T3 (A31) cells; in contrast, epidermal growth factor (EGF) does not activate protein kinase C and is a poor inducer of c-fos and c-myc in these confluent cells. We show that, when A31 cells were subconfluent and made quiescent by serum deprivation, the phorbol ester phorbol 12-myristate 13-acetate induced c-fos and c-myc mRNA poorly, whereas EGF was a better inducer. Another platelet-derived growth factor-inducible gene, JE, did not show this differential regulation by phorbol 12-myristate 13-acetate and EGF. The ability of EGF to induce protooncogene mRNA was associated with elevated levels of intracellular cAMP. First, serum-deprived cells maintained cAMP at about 2-fold higher level than density-arrested cells. Second, induction was greatly enhanced by cholera toxin and 3-isobutyl-1-methylxanthine, which increased intracellular cAMP 3- to 10-fold. The calcium ionophore A23187 mimicked EGF in that it elevated c-fos and c-myc mRNA when administered with cholera toxin and isobutylmethylxanthine. Neither cholera toxin and isobutyl-methylxanthine nor A23187 appreciably induced these mRNAs when used alone. Our results suggest that c-fos and c-myc expression can be regulated by an EGF-directed pathway that utilizes calcium and cAMP as cooperating cytoplasmic messengers.

Regulation of c-myc transcription and mRNA abundance by serum growth factors and cell contact

We describe effects of serum insufficiency and cell contact on the transcription and abundance of the c-myc proto-oncogene mRNA in BALB/c 3T3 fibroblasts. In exponentially growing cells, withdrawal of serum caused a 10-fold decline in c-myc mRNA within 90 min. At least part of this decline was due to a decrease in the level of myc gene transcription. These cells became quiescent at subconfluence after 36-40 h. Cells made quiescent at subconfluence or confluence contained low levels of c-myc mRNA which rose more than 20-fold 2 h after stimulation of growth by fresh serum. Thereafter, the mRNA level declined. In subconfluent cells, it declined to the level in exponentially growing cells, i.e. nearly 10-fold over the level in quiescent cells. In confluent cells, by contrast, the mRNA returned to near-quiescent levels within 18 h (by mid-S phase). However, c-myc gene transcription was regulated identically in subconfluent and confluent cultures; quiescent cells transcribed c-myc at detectable levels, and stimulation by serum caused a 5-fold increase in 1 h, followed by a decline to about 2-fold over the quiescent level within 18 h. Thus, confluence affected steady state mRNA levels without affecting the level of transcription. Our results suggest that extracellular conditions that modulate cell proliferation (serum and cell contact) exert strong and rapid control over c-myc mRNA by post-transcriptional and transcriptional mechanisms.