Paneth cell maturation is related to epigenetic modification during neonatal-weaning transition.

Paneth cells are antimicrobial peptide-secreting epithelial cells located at the bottom of the intestinal crypts of Lieberkühn. The crypts begin to form around postnatal day 7 (P7) mice, and Paneth cells usually appear within the first 2 weeks. Paneth cell dysfunction has been reported to correlate with Crohn's disease-like inflammation, showing narrow crypts or loss of crypt architecture in mice. The morphology of dysfunctional Paneth cells is similar to that of Paneth/goblet intermediate cells. However, it remains unclear whether the formation of the crypt is related to the maturation of Paneth cells. In this study, we investigated the histological changes including epigenetic modification in the mouse ileum postnatally and assessed the effect of the methyltransferase inhibitor on epithelium development using an organoid culture. The morphological and functional maturation of Paneth cells occurred in the first 2 weeks and was accompanied by histone H3 lysine 27 (H3K27) trimethylation, although significant differences in DNA methylation or other histone H3 trimethylation were not observed. Inhibition of H3K27 trimethylation in mouse ileal organoids suppressed crypt formation and Paneth cell maturation, until around P10. Overall, our findings show that post-transcriptional modification of histones, particularly H3K27 trimethylation, leads to the structural and functional maturation of Paneth cells during postnatal development.

Food allergens are transferred intact across the rat blood-placental barrier in vivo.

We investigated the mechanism of transplacental macromolecular transport in rats on the nineteenth day of pregnancy using tracers, transmission electron microscopy and immunohistochemistry. The blood-placental barrier of full-term rat placentas was composed of a trilaminar layer of trophoblast cells that separates the fetal capillaries from the maternal blood spaces: a layer of cytotrophoblasts lining the maternal blood space and a bilayer of syncytiotrophoblast surrounding the fetal capillaries. Horseradish peroxidase, intravenously injected into the maternal circulation, was found in the maternal blood spaces, the interspaces between the cytotrophoblasts and the syncytiotrophoblast I, many pits and small vesicles in the syncytiotrophoblast I, vesicles of the syncytiotrophoblast II, fetal connective tissue and fetal capillaries. Intravenously injected ovalbumin was detected in the maternal blood spaces, a trilaminar layer and the fetal capillaries. Neonatal Fc receptor (FcRn), a receptor for IgG, was localized at the maternal side of the blood-placental barrier. These results show that the structure of the rat blood-placental barrier is quite similar to the human blood-placental barrier, and non-specific macromolecules and food allergens may penetrate through the blood-placental barrier of the full-term placenta from the maternal to fetal circulation mediated by FcRn.

Diamine oxidase as a marker of intestinal mucosal injury and the effect of soluble dietary fiber on gastrointestinal tract toxicity after intravenous 5-fluorouracil treatment in rats.

The level of plasma diamine oxidase (DAO) activity is associated with the maturation and integrity of small intestinal mucosa. This study in rats investigated whether a decreased level of plasma DAO could reflect the severity of mucosal injury due to intravenous 5-fluorouracil (5-FU) treatment. The beneficial effect of soluble dietary fiber (SDF) on preventing diarrhea after 5-FU treatment was also examined. To induce diarrhea, 5-FU (50 mg/kg/day for four days) was administered via the tail vein with or without SDF supplementation. After 5-FU treatment, the majority of rats developed moderate to severe diarrhea, and levels of plasma DAO activity significantly decreased compared to those of control group (P < 0.05). Scanning electron microscopy revealed disarrangement of the small intestinal villi. Contrarily, the rats supplemented with SDF had diarrhea less frequently (50.0 vs. 91.7 %, P = 0.025) on day five, and DAO activity levels were significantly higher than in those rats administered 5-FU alone (8.25 ± 5.34 vs. 5.50 ± 4.32, P = 0.023). In conclusion, plasma DAO activity decreases in response to severe intestinal mucosal injury after 5-FU treatment, and SDF supplementation might be a practical and useful treatment for reducing the intestinal toxicity of 5-FU.

Inhibition of extracellular signal-regulated kinase downregulates claudin-2 expression and alters paracellular permeability in mouse rectum CMT93-II cells.

The morphological and physiological properties of tight junctions (TJs) are determined by the combination and mixing ratios of claudin species. Mouse rectum carcinoma cell lines, CMT93-I and -II cells, expressed claudin-4, -6, -7, and -12, and CMT93-II cells further expressed claudin-2. Although there were no differences in the morphology and number of TJ strands between the two cell lines, transepithelial electrical resistance (TER) of CMT93-II cells was approximately one-seventh that of CMT93-I cells. In this study, we aimed to determine whether claudin-2 expression in CMT93-II cells caused the reduction of TER. Inhibition of the extracellular signal-regulated kinase (ERK) pathway by U0126 treatment for 24 and 48h in CMT93-II cells markedly decreased claudin-2 from the apical junctional region and increased TER. However, claudin-4, -6, and -7 were still continuously localized at the apical junctional region by U0126 treatment. Moreover, the claudin-2 expression recovered at the apical junctional region after the removal of U0126 and TER decreased almost to the baseline level. These results suggest that the ERK pathway positively regulates claudin-2 protein expression and claudin-2 is involved in lowering TER in CMT93-II cells.

Origin of the apical transcytic membrane system in jejunal absorptive cells of neonates.

We investigated the origin of the apical transcytic membrane system in jejunal absorptive cells of neonatal rats using light, electron, and immunofluorescence microscopy. In rats just after birth, intraluminally injected horseradish peroxidase (HRP), used as a macromolecular tracer, was observed only in the apical endocytic membrane system including the lysosomes, of jejunal absorptive cells in vivo. No tracer, however, was found in the intercellular space between the jejunal absorptive cells and the submucosa. Immunoreactive neonatal Fc receptor (FcRn) was localized in the perinuclear region of these absorptive cells whereas immunoglobulin G (IgG) was not found in these absorptive cells. In contrast, in rats 2 h after breast-feeding, intraluminally injected HRP was observed in the apical endocytic membrane system and in the apical transcytic membrane system of the absorptive cells. Moreover, HRP was found in the intercellular space between the jejunal absorptive cells and the submucosa. Furthermore, FcRn and IgG were widely distributed throughout the absorptive cells, and IgG was detected in both the intercellular space and the submucosa. These data suggest that initiation of breast-feeding induces the transportation of membrane-incorporated FcRn from its perinuclear localization to the apical plasma membrane domain. This transportation is achieved through the membrane system, which mediates apical receptor-mediated transcytosis via the trans-Golgi network. Subsequently, the apical plasma membrane containing the FcRn binds to maternal IgG, is endocytosed into the absorptive cells, and is transported to the basolateral membrane domain.

Quality of life, knee function, and physical activity in Japanese elderly women with early-stage knee osteoarthritis.

PURPOSE: To compare quality of life, knee function, and physical activity in 33 elderly women with or without early-stage knee osteoarthritis (OA). METHODS: 33 Japanese elderly women (mean age, 66 years) with (n=18) or without (n=15) early-stage knee OA symptoms (knee pain and decreased range of motion [ROM]) were recruited. The height, weight, and body mass index, disease severity, quality of life (according to the Japanese Knee Osteoarthritis Measure [JKOM]), knee function (knee extension strength, ROM, 10-m gait time), and the amount of physical activity (net energy expenditure and step count) of the 2 groups were compared. RESULTS: The 2 patient groups did not differ significantly with respect to mean patient age, height, and body mass index, except for weight. Regarding knee function, mean knee extension strength, ROM (extension but not flexion), and 10-m gait speed (comfortable and maximum) were significantly inferior in patients with knee OA than in controls. Regarding the mean amount of physical activity undertaken, patients with knee OA did not differ significantly from controls with respect to net energy expenditure (179 vs. 212 Kcal/day) and step count (8016 vs. 9729 steps/day). Net energy expenditure (r= -0.65, p=0.04) and step count (r= -0.62, p=0.02) correlated negatively with JKOM scores in patients with knee OA but not in the controls. CONCLUSION: In Japanese elderly women with knee OA, quality of life (JKOM scores) correlated negatively with physical activity (net energy expenditure and step count). The 2 groups undertook similar amounts of physical activity, although those with knee OA exhibited less knee extension strength. Decreased knee extension strength coupled with high levels of physical activity may exacerbate the development of knee OA.

The expense for one implantation of a banked bone allograft from a cadaveric donor and the issues affecting current advanced medical treatment in the Japanese orthopaedic field.

Demand for banked bone allografts is increasing in Japan; however, there are too few bone banks and the bone bank network is not well-established. One reason for this was lack of funding for banks. Bone banks had to bear all material expenses of banked bone allografts themselves because this was not designated a covered expense. In December 2004, the Japanese government started a new "Advanced Medical Treatment" administration system which allowed an approved institution to charge the expense of authorized advanced medical treatments directly to patients. The treatment named "Cryopreserved allogenic bone and ligamentous tissue retrieved from cadaveric donor" was approved as an advanced medical treatment in March 2007. We present the calculation method and the expense per implantation of a banked bone allograft from a cadaveric donor under this treatment and raise issues which affect this advanced medical treatment and remain to be resolved in the Japanese orthopaedic field.

Blockade of an angiotensin type I receptor enhances effects of radiation on tumor growth and tumor-associated angiogenesis by reducing vascular endothelial growth factor expression.

OBJECTIVE: Angiogenesis, the formation of new capillary blood vessels, is essential for tumor progression. We had reported that Type 1 angiotensin receptor (AT1-R) antagonist reduced tumor-associated angiogenesis. Since antiangiogenic agents were reported to enhance efficacy of radiation therapy, we tested here whether or not AT1-R blockade facilitates the effects of radiation. METHODS: 1 x 10(6) LLC cells were injected into the subcutaneous tissue of male C57BL/6 mice, and when the average tumor volume reached around 0.1 cm(3), radiation doses (3, 5, 10, and 15 Gy) were given on day 1. RESULTS: The mean tumor volumes at day 22 were 6.39 (3 Gy), 6.15 (5 Gy), 5.15 (10 Gy), and 3.07 (15 Gy) cm(3), respectively. Combination of 10 Gy radiation with AT1R antagonist TCV-116 (30 mg/kg) significantly inhibited tumor growth by 83% (1.47 +/- 0.11 cm(3), P < 0.01) in comparison with its inhibition of control tumors (8.81 +/- 0.45 cm(3)). The same was true for mean vessel density, and the combination therapy markedly reduced tumor-associated angiogenesis. This was confirmed by the reduced expression of CD31. LLC tumor growth was blocked by neutralizing antibody against vascular endothelial growth factor (VEGF). Real-time PCR analysis of VEGF disclosed a marked reduction in the mice under combination therapy, compared with control mice. CONCLUSIONS: These results suggest that combination of radiation with AT1-R blockade markedly reduced the LLC growth rate, and that this was due to reduction of neovascularization by reducing VEGF levels. Combination therapy consisting of radiation and AT1R blockade may become an effective novel strategy for cancer treatment.

Molecular morphology of the digestive tract; macromolecules and food allergens are transferred intact across the intestinal absorptive cells during the neonatal-suckling period.

Food allergies represent an important medical problem throughout the developed world. The epithelium of the digestive tract is an important area of contact between the organism and its external environment. Accordingly, we must reconsider the transport of intestinal transepithelial macromolecules, including food allergens, in vivo. The intestinal epithelium of the neonatal-suckling rat is a useful model system for studies into endocytosis and transcytosis. Macromolecules and food allergens can be transferred intact with maternal immunoglobulins across the absorptive cells of duodenum and jejunum during the neonatal-suckling period. This review summarizes these observations as well as our recent molecular morphological studies.

Arthroscopic evaluation after surgical repair of intercondylar eminence fractures.

INTRODUCTION: Patients who undergo surgical repair of intercondylar eminence fracture may have postoperative problems despite good reduction. We used arthroscopy to evaluate the outcomes after surgery to repair intercondylar eminence fractures. MATERIALS AND METHODS: Ten patients (8 men and 2 women; average age at the time of surgery 27.9 +/- 10.0 years, range from 14 to 50 years) with fracture of the tibial intercondylar eminence underwent an arthroscopic reduction and internal fixation with non-absorbable sutures. Preoperative radiological examination showed that there were one Meyer's type-II, eight type-IIIA and one type-IIIB fractures. Clinical symptoms and physical findings for all the patients were evaluated 1 year postoperatively. Radiographic assessment and the Lysholm rating scale were also utilized. Second-look arthroscopy was performed after 1 year when removing the implant. Arthroscopy was used to assess the appearance of the surface of the anterior cruciate ligament (ACL), check for the existence of cyclops and look for interposition of tissue in the lateral and medial joint spaces. RESULTS: One year after the surgery, all ten patients achieved bony union and had negative Lachman and anterior drawer tests. The average Lysholm knee score was 94.5 +/- 7.2 points (range 100-75 points). Arthroscopy showed an irregular surface on the ACL in two of the ten patients, cyclops in two patients, interposition in the lateral joint space in two patients and interposition in the medial joint space in one patient. In the two cases seen with an irregular surface, the ACL was covered with droopy fibrous tissue, but the substance of the ACL was intact. The two patients who had cyclops showed loss of knee extension (5~10 degrees), which was regained by subsequent resection of the cyclops. One patient who had an interposition into the lateral joint space complained of catching, which was released by resection of the interposing tissue. CONCLUSION: Arthroscopic refixation of the intercondylar eminence fracture provided bony union and a good clinical outcome. Cyclops syndrome is one of the causes of loss of knee extension, and soft tissue in the medial or lateral compartment is one of the causes of catching of knee after surgical repair of intercondylar eminence fracture. Cyclops syndrome, which may occur following ACL reconstruction, is one of the causes of loss of knee extension after surgical repair of intercondylar eminence fracture. In patients who have knee complaints, such as catching and loss of knee extension, a second-look arthroscopy is useful for identifying and correcting the problem.

Recruitment of a prostaglandin E receptor subtype, EP3-expressing bone marrow cells is crucial in wound-induced angiogenesis.

E-type prostaglandins have been reported to be proangiogenic in vivo. Thus, we examined prostaglandin receptor signaling relevant to wound-induced angiogenesis. Full-thickness skin wounds were created on the backs of mice, and angiogenesis in wound granulation tissues was estimated. Wound closure and re-epithelization in EP3 receptor knockout mice (EP3-/-) were significantly delayed compared with their wild-type (WT) mice, whereas those in EP1-/-, EP2-/-, and EP4-/- were not delayed. Wound-induced angiogenesis estimated with CD31 immunohistochemistry in EP3-/- mice was significantly inhibited compared with that in WT mice. Immunoreactive vascular endothelial growth factor (VEGF) in wound granulation tissues in EP3-/- mice was markedly less than that in WT mice. Wound closure in WT mice was delayed significantly by VEGF neutralizing antibody compared with control IgG. Wound-induced angiogenesis and wound closure were significantly suppressed in EP3-/- bone marrow transplantation mice compared with those in WT bone marrow transplantation mice. These were accompanied with the reductions in accumulation of VEGF-expressing cells in wound granulation tissues and in mobilization of VEGF receptor 1-expressing leukocytes in peripheral circulation. These results indicate that the recruitment of EP3-expressing cells to wound granulation tissues is critical for surgical wound healing and angiogenesis via up-regulation of VEGF.

Augmentation of intrarenal angiotensin II levels in uninephrectomized aldosterone/salt-treated hypertensive rats; renoprotective effects of an ultrahigh dose of olmesartan.

Recent studies have suggested that aldosterone plays a role in the pathogenesis of renal injury. In this study, we investigated whether local angiotensin II (Ang II) activity contributes to the progression of renal injury in aldosterone/salt-induced hypertensive rats. Uninephrectomized rats were treated with 1% NaCl in a drinking solution and one of the following combinations for 6 weeks: vehicle (2% ethanol, s.c.; n=9), aldosterone (0.75 mug/h, s.c.; n=8), aldosterone+Ang II type 1 receptor blocker olmesartan (10 mg/kg/day, p.o.; n=8), or aldosterone+olmesartan (100 mg/kg/day, p.o.; n=9). Aldosterone/salt-treated hypertensive rats exhibited severe proteinuria and renal injury characterized by glomerular sclerosis and tubulointerstitial fibrosis. Aldosterone/salt-induced renal injury was associated with augmented expression of angiotensin converting enzyme and Ang II levels in the renal cortex and medullary tissues. Renal cortical and medullary mRNA expression of transforming growth factor-beta (TGF-beta) and connective tissue growth factor (CTGF) as well as the collagen contents were increased in aldosterone/salt-treated hypertensive rats. Treatment with olmesartan (10 or 100 mg/kg/day) had no effect on blood pressure but attenuated proteinuria in a dose-dependent manner. Olmesartan at 10 mg/kg/day tended to decrease renal cortical and medullary Ang II levels, TGF-beta and CTGF expression, and collagen contents; however, these changes were not significant. On the other hand, an ultrahigh dose of olmesartan (100 mg/kg/day) significantly decreased these values and ameliorated renal injury. These data suggest that augmented local Ang II activity contributes, at least partially, to the progression of aldosterone/salt-dependent renal injury.

Relationship between glucose transporter and changes in the absorptive system in small intestinal absorptive cells during the weaning process.

In the present study, we investigated the changes in the localization of the glucose transporter GLUT2 and the fructose transporter GLUT5 in small intestinal absorptive cells during postnatal development, especially during the weaning period, using immunohistochemistry and confocal laser scanning microscopy. In the jejunum, GLUT2 was observed within the apical and basolateral membrane domain of absorptive cells, especially in the middle part of the villi. In the suckling rat ileum, GLUT2 was found within the apical and basolateral membrane domain of absorptive cells, but after 18 or 19 days after birth, GLUT2 was found mainly within the apical membrane domain. GLUT5 was observed within the apical membrane domain of absorptive cells in the suckling rat jejunum. In the 18- or 19-day-old rat jejunum, GLUT5 was localized within the apical and basolateral membrane domain of absorptive cells in the lower part of the villi, but after weaning, GLUT5 was found within the apical and basolateral membrane domain of absorptive cells throughout the entire villi. In the suckling rat ileum, there was little GLUT5 in the absorptive cells. In the 18- or 19-day-old rat ileum, GLUT5 was localized within the apical membrane domain of absorptive cells in the lower part of the villi, but after weaning, GLUT5 was observed mainly within the apical membrane domain of absorptive cells throughout the entire villi. These results suggest that the localization of glucose transporters corresponds with a shift from neonatal-suckling to weaned absorptive cells during postnatal development.

Angiotensin type 1a receptor signaling-dependent induction of vascular endothelial growth factor in stroma is relevant to tumor-associated angiogenesis and tumor growth.

Angiotensin II is a multi-functional bioactive peptide and recent reports have suggested that angiotensin II is a proangiogenic growth factor. A retrospective cohort study revealed that angiotensin converting enzyme inhibitors decreased cancer risk, however, the precise mechanism is unknown. We hypothesized that endogenous angiotensin II plays a crucial role in tumor-associated angiogenesis. Tumors implanted in the subcutaneous tissue of wild-type mice developed intensive angiogenesis with vascular endothelial growth factor (VEGF) induction in tumor stroma. AT1a receptor (AT1a-R), but not AT1b receptor or AT2 receptor was expressed in tumor stroma and systemic administration of an AT1-R antagonist reduced tumor-associated angiogenesis and VEGF expression in tumor stroma. Angiotensin II up-regulates VEGF expression through the pathway including protein kinase C, AP-1 and NF-kappaB in fibroblasts, the major cellular component of tumor stroma. VEGF is a major determinant of tumor-associated angiogenesis in the present model, since angiogenesis was markedly reduced by either a VEGF neutralizing antibody or a VEGF receptor kinase inhibitor. Compared with the wild-type, tumor-associated angiogenesis was reduced in AT1a-R null mice, with reduced expression of VEGF in the stroma, and this reduction in AT1a-R null mice was not inhibited by an AT1-R antagonist. These suggest that host stromal VEGF induction by AT1a-R signaling is a key regulator of tumor-associated angiogenesis and tumor growth. AT1a-R signaling blockade may be a novel and effective therapeutic strategy against cancers.

Radiographic comparative evaluation of the Sauve-Kapandji procedure and the Darrach procedure for rheumatoid wrist reconstruction.

For surgical treatment of rheumatoid wrists, we have routinely selected the Sauve-Kapandji (S-K) procedure or the Darrach procedure based on predetermined indications. In this study, we conducted a retrospective radiographic comparative evaluation of the changes in the carpus after the two procedures. The S-K group and the Darrach group each consisted of 13 wrists of 10 patients (all women). The indications for the Darrach procedure were the presence of radiolunate fusion, radial shelf formation, and old age. The carpal height ratio (CHR) and the ulnocarpal distance ratio (UCDR) were determined on wrist radiograms obtained before operation and at the final follow-up. The mean follow-up period was 4 years. Fisher's test was used to analyze the differences between the two groups. Both groups showed a decrease in mean CHR and an increase in mean UCDR at the final follow-up compared to the values before the operation, and there were no statistically significant differences. Furthermore, in the Darrach group, no significant differences in changes of the carpus were observed between patients with or without a radial shelf. We concluded that the present results do not support the superiority of the S-K method over the Darrach procedure for rheumatoid wrist reconstruction based on a radiographic evaluation.

Tibial fractures associated with crush injuries to the soft tissues of the dorsal foot in children.

We retrospectively studied 15 children with tibial fractures associated with crush injuries to the soft tissues of the dorsal foot. The fractures, including six open fractures, were united with no complications within an average of 11.1 weeks. Wound closure to treat crush injuries of the dorsal foot was achieved using split- or full-thickness skin grafts in most patients. The outcomes of these grafts were acceptable, and all skin coverage was successful and remained viable with no breakdown. Extensor tendon injuries of the foot sustained by eight patients could not be sutured or repaired due to the nature of the injuries. However, the functional abilities of those injured tendons that could be sutured to surrounding tissues in a neutral position were acceptable, even though two patients had contracture of the toes that was problematic when wearing shoes. To manage crush skin injuries of the dorsal foot, split- or full-thickness skin grafts appear to provide a simple and convenient treatment strategy. In cases associated with extensor tendon injuries, suturing damaged extensor tendons to surrounding tissues represents another useful strategy with acceptable outcomes.

Endocytosis by absorptive cells in the middle segment of the suckling rat small intestine.

In neonatal suckling rats, the absorptive cells of the duodenum, jejunum and ileum endocytose maternal milk macromolecules, including antibodies from the lumen. To determine whether the absorptive cells from the middle segment of small intestine have an apical endocytic membrane system that is the same as that of the duodenum, jejunum or ileum, we applied horseradish peroxidase by intraluminal injection, and examined the absorptive cells using light and transmission electron microscopy. In the middle segment of the small intestine, the absorptive cells had an apical endocytic membrane system including apical coated pits, apical invaginations, coated vesicles, vesicles, tubules, early endosomes, late endosomes and a large homogeneous electron-dense lysosome at the supranuclear region. This would suggest that the endocytic membrane system in the absorptive cells from the middle segment of the small intestine is specialized for quick and active intracellular digestion. The apical endocytic membrane system of the absorptive cells varied according to the segment of the small intestine, and the absorptive cells made their transition gradually from jejunal type to middle type, and then from middle type to ileal type at the suckling stage. The jejunal and ileal type of absorptive cells increased with growth, in contrast to the middle type.

Blockade of angiotensin AT1a receptor signaling reduces tumor growth, angiogenesis, and metastasis.

It was reported that angiotensin II stimulates angiogenesis in vivo, and angiotensin-converting enzyme (ACE) inhibitors inhibit angiogenesis. We found that an AT1-receptor (AT1-R) antagonist, TCV-116, inhibited tumor growth, tumor-associated angiogenesis, and metastasis in a murine model. Tumor growth of Sarcoma 180 (S-180) cells and of fibrosarcoma (NFSA) cells was strongly inhibited by administration of TCV-116 in the diet at a dose of approximately 100 mg/kg/day. This reduction was accompanied with a marked reduction in tumor-associated angiogenesis. The same treatment also reduced the lung metastasis of intravenously injected Lewis lung carcinoma cells. These effects of TCV-116 were equivalent to those of the ACE inhibitor, lisinopril. In S-180 and NFSA tumor tissues, ACE and AT1a receptor (AT1a-R) mRNAs were expressed when assessed with RT-PCR. AT1b receptor and AT2 receptor, however, were not detected. Immunoreactive AT1-R was detected mainly on the neovascularized vascular endothelial cells in which expression was reduced by TCV-116 and lisinopril. These results suggested that TCV-116 inhibits the angiogenesis, growth, and metastasis of tumors highly dependent on AT1a-R blockade. Blockade of AT1a-R signaling may therefore become an effective novel strategy for tumor chemoprevention.

Cellular differentiation of absorptive cells in the neonatal rat colon: an electron microscopic study.

Cellular differentiation of the absorptive cells in the neonatal-suckling rat colon was investigated using horseradish peroxidase as a macromolecular tracer with a scanning or transmission electron microscope. Numerous villi were lined on oblique folds in an orderly fashion and smaller villi were lined between the folds in the proximal colon in 0- to 12-day-old rats. Three different types of absorptive cells were observed in the epithelium covering their villi: type I cells, type II cells, and type III cells. The type I cells were most numerous, and similar to typical absorptive cells of the adult rat large intestine. The type II cells endocytosed macromolecules into an apical endocytic membrane system without giant lysosome from the large intestinal lumen. The type III cells were characteristic of the well-developed endocytic membrane system, including a large supranuclear giant lysosome specialized for endocytosis, storage, and intracellular digestion as an ileal absorptive cell of the suckling rat. At no time was macromolecular tracer detected in the Golgi apparatus of the absorptive cells or in the intercellular space of the epithelium. These results suggest that the villial absorptive cells of the proximal colon have differentiated to three types at specific neonatal-suckling times. The type II and type III cells were not observed in the epithelium after the disappearance of the villi.