Effect of clofibrate on the small intestine of fetal mice

Summary Pregnant Swiss ICR mice were injected with clofibrate at different dosages and time intervals, and embryos were removed either at 17 or 18 days of gestation. In embryos sacrificed at 17 days the level of intestinal catalase activity of the proximal and distal halves in the treated groups is identical in any case to that of the controls. In embryos sacrificed at 18 days, the rise in the level of catalase activity in the proximal half of the small intestine in treated groups is dose dependent up to a certain limit: with repeated injections the increase reaches a plateau. The distal halves of treated groups are much less responsive and an increase in catalase activity was noted only with repeated injections. In untreated embryos circular DAB-positive microperoxisomes (200 nm in diameter) and tubular structures (100 nm in thickness) are seen in the duodenum at 18 days of gestation. At the same stage, only circular microperoxisomes are identified in the ileum.After clofibrate treatment circular and tubular microperoxisomes are observed in the ileum also. It is concluded that clofibrate induces a rise in catalase activity in the embryo, only after 17 days of gestation. These observations are discussed in relation to the biogenesis of microperoxisome.Supported by Grant No. MA-6069 from the Medical Research Council of CanadaMr. D. Malka was supported by a studentship from the FCAC of the province of QuebecDr. D. Ménard is a Chercheur boursier du Conseil de la Recherche en Santé du Québec     

Effect of syngeneic thymocytes on the proliferation of the small intestine epithelium in mice

The effect of syngeneic thymocytes on the proliferative compartment of the small intestinal epithelium was studied in CBA mice. In mice that intravenously received thymus cells, the proliferative enterocyte activity was depressed, the proliferative zone reduced and the maturation zone enlarged. The data obtained indicate that medullary thymocytes are responsible for this effect. The regulatory role of the immune system with regard to cell proliferation is discussed.     

Endocrine cells in the human fetal small intestine

Summary In this report we describe the time of appearance and ultrastructural features of enteroendocrine cells (EECs) in the human fetal small intestine (SB) between 9 and 22 weeks gestation. Thirteen distinctive EECs were identified in fetal SB. Two of these, not found in normal adult SB, appeared within the stratified epithelium of the proximal SB at 9–10 weeks. They were arbitrarily termed primitive and precursor cells. As in all fetal EECs, the pale cytoplasm of the primitive cell contains a distinctive population of secretory granules (SGs). Primitive cell SGs average 200–330 nm; some have dense cores with lucent halos while others are filled with a homogeneous dense or flocculent material. The SGs of the precursor cells are larger, averaging up to 1 m in diameter and their contents vary in electron density. A third group of cells not described in normal adult SB was arbitrarily termed transitional cells. These have two populations of SGs; one resembles the SGs of the precursor cells, and the other resembles the SGs of some of the specific adult type EECs. Transitional EC, S, I and G cells are seen. In addition, mature appearing EC, S, G, I, L, D, and D₁ cells were identified by 12 weeks of gestation. The primitive, precursor, and transitional cells may represent sequential developmental precursors of adult type EECs.Supported by Research Grant AM-17537 from the National Institutes of Health, Besthesda, MarylandThe authors would like to thank Ms. Linda Barstein for her excellent technical assistance     

Histochemical studies of developing human fetal small intestine

Summary The histochemical characteristics of absorptive and mucus-producing cells have been described in 16 specimens of small intestine from human fetuses between 7 and 22 weeks of age. In the youngest specimens a slight to moderate reaction was found for all enzymes examined which included those known from biochemical or ultrastructural studies to be located predominantly in Golgi apparatus (thiamine pyrophosphatase), surface membrane (alkaline phosphatase, adenosine triphosphatase, leucine aminopeptidase), lysosomes (acid phosphatase), and mitochondria (succinic dehydrogenase). Mucus granules of somehat unusual location and staining properties were also found at this time. A progressive intensification of a majority of these histochemical reactions was observed between 3 and 6 fetal months.These findings indicate that the histochemical apparatus for degradation and absorption of nutrients and for elaboration of protein and mucus is already well established in the human fetus by the end of this 6 month period. It is not known, however, whether these activities occur in utero or whether they contribute significantly to fetal nutrition.     

Enhancement by dietary clofibrate of peroxisomal palmityl-CoA oxidase in kidney and small intestine of albino mice and liver of genetically lean and obese mice

Using density gradient fractionation palmityl-CoA oxidase was localised in the peroxisomes of kidney and small intestine of albino mice. Dietary clofibrate treatment for 14 days resulted in significant increases in palmityl-CoA oxidase of kidney and small intestine of albino mice and liver of genetically lean and obese mice, and was accompanied in the latter by a proliferation of hepatic peroxisomes.     

Junctional complexes in fetal rat small intestine during morphogenesis

During the 7 days prior to birth (Days 15–22), the small-intestinal epithelium of the fetal rat changes from primitive stratified to simple columnar epithelium which lines villi at 19 days. As seen in thin sections, this remodeling involves rapid formation of new junctional complexes and secondary lumens between epithelial cells deep in the stratified epithelium. We have examined the formation and reorganization of junctional complexes in proximal small intestine of 15- to 19-day fetal rats using freeze-fracture techniques. On Days 15 and 16 the epithelial cells surrounding the primary lumen are joined by conventional apical junctional complexes. Additionally, macular junctional complexes are located on deeper epithelial cells. These display no polarity and consist of tight-junction strands intermixed with gap junction-like arrays and desmosomes. On Days 17 and 18 nonluminal, macular junctional complexes enlarge and secondary lumens develop within their centers. As the secondary lumens expand, microvilli appear and the junctional complex polarizes about the secondary lumen; tight-junction strands become parallel to the luminal surface, desmosomes migrate basolaterally, and gap junction-like arrays disappear. By Day 19, secondary lumens have fused with the primary lumen; concomitant loss of apical cells results in formation of villi lined by simple columnar epithelium with polarized apical tight junctions. The observed pattern of junctional complex formation may play a role in maintaining barrier function and establishing epithelial cell polarity as the epithelium is remodeled.     

Insulin decreases chylomicron production in human fetal small intestine.

The objective of this study was to examine the effect of insulin on lipoprotein synthesis and secretion in human fetal intestine. Jejunal explants were cultured with [14C]oleic acid in Leibovitz medium for 42 h. Although the addition of insulin (30 U) did not alter the incorporation of [14C]oleic acid into triglycerides, phospholipids and cholesteryl esters in the tissue, it significantly decreased (P < 0.05) the level of triglycerides (20%) in the medium. Among the three lipoprotein classes (chylomicron, VLDL, and HDL) isolated by ultracentrifugation, the chylomicron level was found significantly (P < 0.05) diminished in the medium (29%). Neither the lipid chemical composition of CM or that of VLDL, LDL and HDL was affected by the presence of insulin. These results suggest that chylomicron synthesis is modulated by insulin, whereas lipoprotein distribution and lipid composition are not regulated by this hormone.     

Permissive effect of glutamine on the differentiation of fetal mouse small intestine in organ culture

The proximal third of the small intestine of 15-day-old mouse embryo can be cultured for 72 h at 37 degrees C. When Trowell-T8 medium is used, the integrity of the explants is maintained, but villi do not form and absorptive cells are poorly differentiated. However, when Leibovitz L-15 or RPMI-1640 medium is used, one can observe the formation of medium-sized villi, and absorptive cells in the explants are more differentiated. Since the chemical composition of T8 medium is quite different from that of the other two media, we decided to test the importance of two major differences, i.e., three amino acids and five vitamins, in order to find out which element(s) is necessary to permit the formation of intestinal villi. Subsequent testing demonstrated that the three amino acids are responsible for the effect on differentiation, and that glutamine is the only critical difference between T8 and the two other media. The results show that the addition of L-glutamine to T8 medium permits the formation of villi, the initiation of absorptive cell differentiation, an increase in DNA synthesis, and finally, an increase in the number of epithelial cells. These findings indicate that undifferentiated fetal mouse small intestine is able to express its phenotype in organ culture, even without any extrinsic regulatory influences, provided that L-glutamine is present at a sufficient level in the culture medium. The use of inhibitors indicated that L-glutamine may be essential as an energetic substrate and/or a precursor for glucosamine.     

Nafenopin-induced proliferation of peroxisomes in the small intestine of mice.

The effect of nafenopin on the epithelial cells of the small intestine of mice was studied. After 17 days the control and nafenopin-treated groups were sacrificed. The tissues were incubated in alkaline DAB medium. Ultra-thin sections of small intestinal tissue from both groups were examined by electron microscopy. Electron micrographs were prepared and examined stereologically so that any morphologic differences in the epithelial cell peroxisomes and mitochondria between the experimental and control groups could be evaluated quantitatively. In the nafenopin-treated group proliferation of peroxisomes occurred, as indicated by significant increases in volume, and surface and numerical density of these structures compared with controls. No such alterations were found in the mitochondria. Our results show that the response of small intestinal epithelial cells to nafenopin is analogous to that produced in hepatocytes by the same drug. Hepatocyte peroxisomes are supposed to be involved in lipid metabolism and it seems that small intestinal epithelial peroxisomes play a similar role.