Clear evidence for element partitioning effects in a Ti-6Al-4V alloy by the first-principles phase field method

Ti-6 wt% Al-4 wt% V (Ti64) is an α + β titanium alloy, in which the alloying components strongly affect the mechanical properties. In this report, element partitioning effects in Ti64 are investigated by using the first-principles phase field (FPPF) method, which has recently been proposed by our group. In the FPPF method, the local free energy is calculated using a cluster expansion method in combination with density functional theory and the temperature effect is incorporated using potential renormalization theory. We have succeeded in identifying enrichment of Al (V) in the α (β) phase, i.e., the clear evidence for the element partitioning effects of Al and V, without using any thermodynamical parameter. The transformation of the β phase and the α phase in microstructure is investigated by varying the V and Al concentrations by a small amount. Our results are in excellent agreement with the recent experimental results, showing the validity of the FPPF method for ternary alloys.

PROTECTIVE EFFECT OF LIFETIME EXPERIENCES ON FUNCTIONAL STATUS IN YOUNG-ONSET DEMENTIA

Patients with Frontotemporal degeneration (FTD), a common form of young-onset dementia, experience decline in cognitive, social and daily functioning as the disease progresses. Research shows that lifestyle factors may be an important modifiable risk factor for dementia, but this has not been well studied in FTD. In this study, we test the hypothesis that lifetime experiences, including education, occupation, and leisure activities, are associated with better functional status in individuals with FTD. We also evaluated the relationship between timing of experiences (early, mid-life, and late-life) and functional status. Thirty-five patients (mean age 61.6±8.7; 74% male; mean disease duration 3.4 ± 2.6; mean MMSE 24.0 ± 5.5) completed the Lifetime of Experiences Questionnaire (LEQ), a comprehensive assessment of lifelong cognitive lifestyle, and the Clinical Dementia Rating Scale (CDR), which was used to assess functional status. Linear regression tested the relationship between cognitive lifestyle and functional status, with age and disease duration included as covariates. Higher total LEQ score was associated with better functional status (lower score on CDR) (β = -0.047, p = 0.009). While Young Adulthood LEQ score was not significantly associated with total CDR (β = -0.047, p = 0.176), both Mid-life (β = -0.117, p = 0.011) and Late-life (β = -0.133, p = 0.013) LEQ score significantly contributed to functional status. Our results indicate that functional status is mediated in part by cognitive lifestyle and that experiences accumulated in mid-life and late-life have a greater effect on functional status at time of diagnosis.

Progress towards rabies control and elimination in Vietnam

Rabies is a fatal viral disease that causes an estimated 59,000 human deaths each year. The majority of these deaths occur in developing countries in Asia. Canine rabies is endemic to Vietnam, which is, however, moving towards the disease's elimination. Many countries, such as Vietnam, have invested tremendous resources in controlling rabies, highlighting the goal of regional and global elimination of this neglected disease. In Vietnam, rabies is recognised as one of five high-priority, zoonotic diseases by the Ministry of Health and the Ministry of Agriculture and Rural Development. Investment by the government and by international partners for rabies prevention and control has played a substantial role in reducing human rabies deaths from 404 cases in 1992 to 74 cases in 2017. The catalyst for this effort was the Prime Minister's creation of the National Rabies Program in 1996, which led to increased support and resources for rabies prevention and control. Interventions carried out since then include the expansion of post-exposure prophylaxis centres throughout the country, the introduction or revision of key legislation and guidelines, and improved multisectoral One Health collaboration. In addition, support from international partners, such as the World Organisation for Animal Health (OIE), the World Health Organization (WHO), the Food and Agriculture Organization of the United Nations (FAO), and the Centers for Disease Control and Prevention (CDC), has helped to increase awareness, manage dog populations more effectively, and improve Vietnam's surveillance and diagnostic capabilities. To pursue the goal of eliminating dog-mediated rabies in Vietnam, political commitment is crucial. Resources must be made available to enforce the regulations and guidelines that will enable Vietnam to achieve greater canine rabies vaccination coverage. In this paper, the authors provide an overview of the animal and human health systems in Vietnam, as well as past, current and future directions of rabies prevention and control.

Prospective observational study comparing burn surgeons' estimations of wound healing after skin grafting to photo-assisted methods

INTRODUCTION

Appropriate graft healing after split-thickness skin graft and early recognition of complications (graft loss) are critical to burn patient management. Larger mesh ratio expansions and Meek micrografting may pose a greater challenge in estimating the percentage of wound healing. This study looks at the reliability of photograph assessments and the concordance of bedside evaluation to photograph assessments of wound healing after skin grafting.

METHODS

Three assessment methods for percentage of wound healing after skin Grafting were assessed: (1) clinicians' bedside rating, (2) clinician assessment of high-definition photographs, and (3) digital image analysis through color subtraction using Adobe Photoshop. We compared each method using a mixed-effects model on absolute agreement using intra-class correlation (ICC) and Bland Altman (BA) plots.

RESULTS

Fourteen burn patients were enrolled with 38 grafted wounds (100 sites). Bedside assessments had a mean ICC of 0.64 (compared to digital image analysis) and 0.69 (compared to photo assessment), with a wide range on BA-plots. Inter-rater reliability of photo assessment was excellent (0.96) among six clinicians. Repeated photo-assisted assessments had good intra-rater reliability (ICC: photo assessment: 0.88; digital analysis: 0.97).

CONCLUSIONS

Bedside wound healing assessments show variability; photograph documentation of sequential wound progression could supplement active clinical management or studies for more reliable assessments.

CD14-mediated alterations in transcription and splicing of endogenous retroviruses after injury

Increase in systemic levels of lipopolysaccharide (LPS) contributes to the pathogenesis of distant organ injury after burn. Stress signals elicited from burn influence transcriptional activities of mouse endogenous retroviruses (MuERVs) in various distant organs. The involvement of LPS pathways in the burn-mediated regulation of MuERVs in the spleen was investigated in this study. Spleen harbors substantial numbers of tissue macrophages, a key responder to LPS stimulation. Spleen tissues collected from CD14 (LPS receptor) knockout (KO) and wild type (WT) mice after burn were subjected to RT-PCR analysis of MuERV expression. There was a substantial induction of 2 bands and a marked downregulation of a band in CD14 KO mice compared to WT mice after burn. Sequence analysis of these CD14- and burn-dependent bands identified 3 new alternatively spliced and 2 defective env transcripts of MuERVs as well as novel splicing signals. Chromosomal loci of putative MuERVs sharing the unique U3 sequences of these transcripts were mapped by surveying the entire genome of C57BL/6J mice. In addition, coding potentials, transcriptional regulatory elements, and adjacent cellular genes of these putative MuERVs were analyzed. The results from these studies suggest that injury-triggered LPS/CD14 signaling events play roles in the transcriptional regulation of certain MuERVs carrying unique U3 promoter sequences.

Protein thioacylation: 2. Reagent stability in aqueous media and thioacylation kinetics

Several thioacylating reagents have been tested toward hydrolysis under conditions suitable for protein modifications: 20-35 degrees C and buffered solutions at pH 7.5-8.5. Aliphatic dithioesters are sufficiently stable in aqueous media at room temperature (or below) if protein modification reaction time does not exceed 24 h, whereas at 35 degrees C reaction times must be limited to a few hours. Kinetic data obtained in gelatin thioacylation at room temperature using aliphatic dithioesters and dithio acid are consistent with a second-order reaction rate with respect to amine concentration. The pH dependence of the second-order reaction rate constants indicate that dithioester reacts exclusively with the free amine form of lysine residue, whereas dithiocarboxylate ion reacts with both amine and ammonium ion, probably through a more complex mechanism. Interestingly thioacylation using dithio acids may be obtained in pH near neutrality or in slightly acidic media, thus offering protein modification possibilities at pH 5-9. Thioacylation reaction rates may be expressed as R = -(dAt/dt) = k[H3O+](-b)At2[thioacylating agent] in which At is the amine concentration at time t, constants k and b depending on the reagent nature.

Protein thioacylation. 1. Reagents design and synthesis

Thioacylation is a new way for protein chemical modification. Carboxylic dithioesters and -acids react selectively and rapidly at room temperature with aliphatic amines such as lysine epsilon-amino groups leading to thioamide formation, without any other reagent or catalyst. Various thioacylating reagents were synthesized: monofunctional dithioesters bearing on the acylating end various chemical groups such as: aliphatic chains, phenyl group, mono- and dicarboxylic acids, dialkylphosphonic ester, phosphonic acid, thiol, phenol, or quaternary ammonium group. Bifunctional dithioesters containing either a polymethylene chain or an ethylene oxide oligomer as spacer group as well as some mono- and bis(dithio acids) are described. Applications of thioacylation may be involved either in enzyme chemical modifications or in the obtention of new materials from proteins. Bifunctional reagents might be used as cross-linking or coupling reagents.

Identification of the configuration of neosartorin by long-range nuclear Overhauser effect measurements

The relative configuration of the two xanthene units of neosartorin, a new ergochrome biosynthesised by the soil mould Neosartorya fischeri, was determined using a 1D double-pulsed field gradient spin-echo NOESY experiment. It was found that both units have the same relative stereochemistry. Long-range nonbonding interactions between the substituents of different xanthene units stabilise the nonplanar configuration of the two aromatic rings A and A' connecting both monomer units of neosartorin.

Results of early excision and full-thickness grafting of deep palm burns in children

The timing and method of treatment of deep palm and finger burns varies widely. Our protocol involves performing full-thickness skin grafts (FTSG) in nonhealing palm burns. We reviewed the functional and cosmetic results after FTSG to the palm. From August 1997 to April 1999, 11 patients (12 palms) underwent excision and FTSG within 2 weeks of injury. A panel of medical and nonmedical professionals evaluated follow-up pictures of the grafts at 1, 2 to 4, and beyond 4 months. Parameters used for evaluation were color match with the unburned skin (1 = no difference to 4 = large difference), graft thickness (1 = flat to 4 = markedly raised), overall appearance (1 = poor to 100 = excellent), and time to maturity. Hand function, as assessed by occupational therapy notes, was also recorded. All 12 grafted palms had a 100% take and healed with minimal scarring. Mean color match scores were 2.4 at 1 month, 1.8 at 2 to 4 months, and 1.6 beyond 4 months. On the graft thickness scale, grafts were given scores of 2.6, 2.2, and 1.9 during the same intervals. The overall appearance was 71 at 1 month, 81 at 2 to 4 months, and 85 beyond 4 months. All grafts except 1 were judged to be mature at 2 to 4 months follow-up. Full passive range of motion was attained in all grafted hands within the period of 2 to 4 months after operation. Early excision and FTSG of deep pediatric palm burns can be performed in the outpatient setting. The grafts have an acceptable color match, are minimally raised, and achieve excellent cosmetic result. The grafts mature within a few months after surgery to allow for rapid return to normal range of motion. FTSG should be considered as a first choice for deep palm burns.

A study of creatine kinase reaction in rat brain under chronic pathological conditions-chronic ischemia and ethanol intoxication

Creatine kinase reaction rates were measured by the magnetisation transfer technique in brains of healthy adult and aged rats and in rats with chronic cerebral ischemia and chronic ethanol intoxication. These measurements indicated that the rate constant of the creatine kinase reaction is significantly reduced in the case of severe chronic cerebral ischemia in aged rats. In the adult rats, during chronic ethanol intoxication after 3 weeks of administration of 3 ml of 30% ethanol once a day via a gastric tube, a significant decrease in the pseudo first-order rate constant k(for) of the creatine kinase reaction was also found. In contrast, mild chronic cerebral ischemia in adult rats produced an increase in the reaction rate 4 weeks after occlusion. At the same time, corresponding conventional phosphorus magnetic resonance spectra showed negligible changes in signal intensities.

Radiographic changes after colonoscopic decompression for acute pseudo-obstruction

PURPOSE

Colonoscopy has been the principal tool for decompression in acute colonic pseudo-obstruction, known as Ogilvie's syndrome. The objectives of this study were to determine the immediate effect of colonoscopy on the cecal diameter (measured on supine radiographs) and to delineate possible correlations in the diameters of dilated segments of the colon.

METHODS

The charts and radiographs of 24 patients who had colonoscopic decompression for acute colonic pseudo-obstruction between 1992 and 1997 at the San Diego Veterans Affairs Medical Center and the University of California, San Diego Hospitals were reviewed. We measured cecal, transverse, descending, and sigmoid colon diameters on serial radiographs up to the point of clinical resolution.

RESULTS

Mean +/- standard deviation cecal diameter change (between initial and post-decompression films) was -2+/-3.4 cm at four hours and -2.2+/-3.3 cm one day after decompression. On the daily radiographs between colonoscopic decompression and clinical resolution, there was a close correlation between the diameter of the cecum and that of the transverse colon (P<0.05). There was no correlation between the cecal diameter and that of the descending or sigmoid colon.

CONCLUSIONS

Colonoscopic decompression only causes a small decrease in cecal size in the patient with acute colonic pseudo-obstruction. Dilation patterns of the cecum and transverse colon are significantly correlated in acute colonic pseudo-obstruction. This correlation provides additional support to the contention that the same pathophysiology affects these two segments of the colon.

Multistep denaturation of Borrelia burgdorferi OspA, a protein containing a single-layer beta-sheet

Outer surface protein A (OspA) from the Lyme disease spirochete, Borrelia burgdorferi, is a dumbbell-shaped protein in which two globular domains are connected by a three-stranded beta-sheet segment that is solvent-exposed on both faces. Previous studies showed that the whole protein, including the single-layer beta-sheet, is highly rigid. To elucidate the folding mechanism and the role of the central beta-sheet in the formation of the rigid molecule, we investigated the equilibrium thermal denaturation reaction of OspA. We applied differential scanning calorimetry, heteronuclear NMR spectroscopy, and solution small-angle X-ray scattering (SAXS) to characterize the reaction in detail. All three techniques revealed that OspA denatures in two separable cooperative transitions. NMR measurements on OspA specifically 15N-labeled at Lys residues identified the locations of the two folding units and revealed that the C-terminal segment is less stable than the remaining N-terminal segment. The boundary between the two folding units is located within the central beta-sheet. The interconversion among the three folding states (fully folded, C-terminus unfolded, and fully denatured) is slow relative to chemical shift differences (<24 Hz), indicating that there are significant kinetic barriers in the denaturation reactions. SAXS measurements determined the radius of gyration of the native protein to be 25.0 +/- 0.3 A, which increases to 34.4 +/- 1.0 A in the first transition, and then to 56.1 +/- 1.6 A in the second transition. Thus, the intermediate state, in which the C-terminal folding unit is already denatured, is still compact. These results provide a basis for elucidating the folding mechanism of OspA.

Multistep denaturation of Borrelia burgdorferi OspA, a protein containing a single-layer beta-sheet

Outer surface protein A (OspA) from the Lyme disease spirochete, Borrelia burgdorferi, is a dumbbell-shaped protein in which two globular domains are connected by a three-stranded beta-sheet segment that is solvent-exposed on both faces. Previous studies showed that the whole protein, including the single-layer beta-sheet, is highly rigid. To elucidate the folding mechanism and the role of the central beta-sheet in the formation of the rigid molecule, we investigated the equilibrium thermal denaturation reaction of OspA. We applied differential scanning calorimetry, heteronuclear NMR spectroscopy, and solution small-angle X-ray scattering (SAXS) to characterize the reaction in detail. All three techniques revealed that OspA denatures in two separable cooperative transitions. NMR measurements on OspA specifically 15N-labeled at Lys residues identified the locations of the two folding units and revealed that the C-terminal segment is less stable than the remaining N-terminal segment. The boundary between the two folding units is located within the central beta-sheet. The interconversion among the three folding states (fully folded, C-terminus unfolded, and fully denatured) is slow relative to chemical shift differences (<24 Hz), indicating that there are significant kinetic barriers in the denaturation reactions. SAXS measurements determined the radius of gyration of the native protein to be 25.0 +/- 0.3 A, which increases to 34.4 +/- 1.0 A in the first transition, and then to 56.1 +/- 1.6 A in the second transition. Thus, the intermediate state, in which the C-terminal folding unit is already denatured, is still compact. These results provide a basis for elucidating the folding mechanism of OspA.

NMR studies of Borrelia burgdorferi OspA, a 28 kDa protein containing a single-layer beta-sheet

The crystal structure of outer surface protein A (OspA) from Borrelia burgdorferi contains a single-layer beta-sheet connecting the N- and C-terminal globular domains. The central beta-sheet consists largely of polar amino acids and it is solvent-exposed on both faces, which so far appears to be unique among known protein structures. We have accomplished nearly complete backbone H, C and N and C beta/H beta assignments of OspA (28 kDa) using standard triple resonance techniques without perdeuteration. This was made possible by recording spectra at a high temperature (45 degrees C). The chemical shift index and 15N T1/T2 ratios show that both the secondary structure and the global conformation of OspA in solution are similar to the crystal structure, suggesting that the unique central beta-sheet is fairly rigid.

A stable single-layer beta-sheet without a hydrophobic core

Outer surface protein A from the Lyme disease spirochete Borrelia burgdorferi contains a single-layer beta-sheet connecting the N- and C-terminal globular domains. The central beta-sheet consists largely of polar amino acids and is solvent-exposed on both faces, which so far appears to be unique among known protein structures. We show that the single-layer beta-sheet segment is surprisingly stable (deltaG for hydrogen exchange is approximately 8 kcal mol(-1) at 45 degrees C). Possible factors contributing to the stability of the single-layer beta-sheet are discussed based on an analysis of the crystal structure.

Comparison of a direct and indirect population pharmacodynamic model: application to recombinant human erythropoietin in athletes

Basic physiologic indirect response models have been proposed to account for the pharmacodynamics of drugs that act by way of inhibition or stimulation of the production or loss of endogenous substances or mediators. In this work, these models were applied to account for the effects of recombinant human erythropoietin (rHuEpo) in man. Indeed, rHuEpo induces a delayed increase of serum soluble transferrin receptors (sTfr) and a delayed decrease in ferritin (fr) concentrations. The purpose of the present study was to compare two pharmacodynamic approaches to relate serum erythropoietin (Epo) concentrations to the effect of rHuEpo on sTfr, and fr, the "indirect effect" and the "effect compartment" models. However, due to the average lag time of about 50 hr between the first intake of rHuEpo and the onset of the measurable effects, a delay function was incorporated into the "indirect response models" to describe the relationship between the Epo plasma concentrations and the endogenous receptors or mediators affected by the drug and responsible for the effects on sTfr and fr. There are no real differences in the descriptive features of the two models used. For these reasons, the indirect model seems more appropriate because it supplies a possible mechanistic interpretation of the physiological process.

Cyclodextrins and enantiomeric separations of drugs by liquid chromatography and capillary electrophoresis: basic principles and new developments

Investigation of individual drug enantiomers is required in pharmacokinetic and pharmacodynamic studies of drugs with a chiral centre. Cyclodextrins (CDs) are extensively used in high-performance liquid chromatography as stationary phases bonded to a solid support or as mobile phase additives in HPLC and capillary electrophoresis (CE) for the separation of chiral compounds. We describe here the basis for the liquid chromatographic and capillary electrophoretic resolution of drug enantiomers and the factors affecting their enantiomeric separation. This review covers the use of CDs and some of their derivatives in studies of compounds of pharmacological interest.

Expression of Bombyx family fungal protease inhibitor F from Bombyx mori by baculovirus vector

Fungal protease inhibitor F (FPI-F) from silkworm hemolymph is a novel serine protease inhibitor of the Bombyx family. The cDNA of FPI-F was introduced into a baculovirus vector and a recombinant virus was isolated and plaque-purified. The protease inhibitory activities increased in the culture medium of insect cells and in the hemolymph of silkworms infected with the recombinant virus. Judged from the behavior on ion-exchange and reversed-phase chromatographies, amino acid compositions, amino-terminal sequences, and CD spectra, the recombinant FPI-F was identical with native FPI-F. Infection with the recombinant virus caused inhibition of larval development of the silkworm. However, the degree of the effect was different in two strains, Shinryukaku and Taiheichoan, indicating that the selection of the strain of silkworm is important in using the baculovirus expression system.

A new family of serine protease inhibitors (Bombyx family) as established from the unique topological relation between the positions of disulphide bridges and reactive site

The positions of the reactive site and the disulfide bridges in fungal protease inhibitor F (FPI-F) from silkworm (Bombyx mori), which has a unique amino acid sequence and inhibitory specificity, were investigated. At pH 3.0, subtilisin BPN', which is one of target proteases of this inhibitor, specifically cleaved the peptide bond of the inhibitor at Thr(29)-Val(30). The cleaved bond was regenerated by subtilisin BPN' at pH 8.0. These results indicate that the Thr(29)-Val(30) bond of the inhibitor is the reactive site. The locations of disulfide bridges were determined to be Cys(3)-Cys(35), Cys(14)-Cys(27), Cys(18)-Cys(55), and Cys(37)-Cys(49). Based on the positions of the reactive site and the disulfide bridges, FPI-F is considered to be a member of a new family of serine protease inhibitors. We propose the designation Bombyx family for the new inhibitor family of which FPI-F is a member.

Trypsin and elastase inhibitors from bitter gourd (Momordica charantia LINN.) seeds: purification, amino acid sequences, and inhibitory activities of four new inhibitors

Serine proteinase inhibitors of the squash family were isolated from bitter gourd (Momordica charantia LINN.) seeds by the conventional purification method. Heat treatment of the extract of the seeds allowed removal of large amounts of protein without loss of trypsin and elastase inhibitory activities. From the supernatants thus obtained, the inhibitors were isolated to homogeneity by ion-exchange chromatography, gel filtration, and reversed phase chromatography. One trypsin inhibitor (Momordica charantia trypsin inhibitor-III; MCTI-III) and three elastase inhibitors (Momordica charantia elastase inhibitor-II, -III, and -IV; MCEI-II, -III, and -IV) were newly isolated in addition to trypsin inhibitors MCTI-I and -II and elastase inhibitor MCEI-I previously reported [Hara, S. et. al. (1989). J. Biochem. 105, 88-92]. The primary structures of the four new inhibitors were determined as follows. [sequence: see text] The dissociation constants, Ki, of MCTI-III complex with bovine beta-trypsin, and of MCEI-II, -III, -IV with porcine elastase were determined to be 1.9 x 10(-7) M, 9.4 x 10(-9) M, 4.0 x 10(-9) M, and 4.7 x 10(-9) M, respectively. Although MCTI-III differed from MCTI-I in only two amino acids, having Gly(3) and Gln(13) in place of Arg(3) and Arg(13), the Ki value of MCTI-III was 20-fold larger than that of MCTI-I. Addition of an amino terminal Glu residue, a dipeptide (Glu-Glu-), and a tripeptide (Glu-Glu-Glu-) to MCEI-I strengthened its elastase inhibitory activity by 200-fold.

Sequence analyses and evolutionary relationships among the energy-coupling proteins Enzyme I and HPr of the bacterial phosphoenolpyruvate: sugar phosphotransferase system

We have previously reported the overexpression, purification, and biochemical properties of the Bacillus subtilis Enzyme I of the phosphoenolpyruvate: sugar phosphotransferase system (PTS) (Reizer, J., et al., 1992, J. Biol. Chem. 267, 9158-9169). We now report the sequencing of the ptsI gene of B. subtilis encoding Enzyme I (570 amino acids and 63,076 Da). Putative transcriptional regulatory signals are identified, and the pts operon is shown to be subject to carbon source-dependent regulation. Multiple alignments of the B. subtilis Enzyme I with (1) six other sequenced Enzymes I of the PTS from various bacterial species, (2) phosphoenolpyruvate synthase of Escherichia coli, and (3) bacterial and plant pyruvate: phosphate dikinases (PPDKs) revealed regions of sequence similarity as well as divergence. Statistical analyses revealed that these three types of proteins comprise a homologous family, and the phylogenetic tree of the 11 sequenced protein members of this family was constructed. This tree was compared with that of the 12 sequence HPr proteins or protein domains. Antibodies raised against the B. subtilis and E. coli Enzymes I exhibited immunological cross-reactivity with each other as well as with PPDK of Bacteroides symbiosus, providing support for the evolutionary relationships of these proteins suggested from the sequence comparisons. Putative flexible linkers tethering the N-terminal and the C-terminal domains of protein members of the Enzyme I family were identified, and their potential significance with regard to Enzyme I function is discussed. The codon choice pattern of the B. subtilis and E. coli ptsI and ptsH genes was found to exhibit a bias toward optimal codons in these organisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of growth-stimulating activity in the proximal small intestine during weaning in the suckling rat

Adaptive changes in enzyme expression and cell proliferation occur in the small intestine of the suckling rat at the beginning of the 3rd postnatal week. This physiological adaptation can be modulated by factors including diet or glucocorticoids. We have previously described an intestinal growth-stimulating fraction derived from the remnant small bowel after resection and found that enteral nutrition is critical for its detection. In view of the similarity between the changes in cell proliferation that occur between 15 and 22 days postnatally and those immediately after resection, we sought to determine whether the small intestinal mucosa of the neonatal rat also contains a similar growth-stimulating fraction. Our results show that extracts of the proximal intestine prepared from 15-day-old rats do contain the growth-stimulating fraction. The activity was not detectable in maternal milk nor in the intestinal extract from 8-day-old rats. When the suckling rats were deprived of solid food, the activity was not detectable in the 15-day-old group. Gel filtration of the acidic extract on a G-25 Sephadex column revealed that the active component is made up of two molecular weight species (approximately 4,500 and 1,500 daltons) similar to that described in the proximal intestine of the postresectional model. These findings suggest that dietary factors may play a role in modulating the proliferative changes that occur at the time of weaning by way of the growth-stimulating fraction.