Brush Border Hydrolases Research Articles

Intracellular transport and conformational maturation of intestinal brush border hydrolases.

Brush border hydrolases of the differentiated intestinal cell line Caco-2 are transported to the microvillar membrane at different rates. This asynchronism is due to at least two rate-limiting events, a pre- and an intra-Golgi step. The retardation of sucrase-isomaltase, a slowly migrating hydrolase, versus dipeptidylpeptidase IV, a rapidly transported enzyme, is neither due to differential trimming of N-linked carbohydrates nor due to oligomerization. In this study, the conformational maturation of biosynthetically labeled sucrase-isomaltase and dipeptidylpeptidase IV was probed by conformation-specific antibodies and proteases. These assays enabled us to correlate the conformational maturation of the two enzymes with their rates of transport. Furthermore, two naturally occurring mutants of sucrase-isomaltase with impaired intracellular transport displayed an immature conformation. It is proposed that differential kinetics of folding might be the underlying cause for both the pre- and the intra-Golgi steps of asynchronous intracellular transport. Furthermore, a proper tertiary structure might be a prerequisite for sucrase-isomaltase to leave the Golgi apparatus.

Fetal mouse kidney maturation in vitro: Coordinated influences of epidermal growth factor, transferrin and hydrocortisone

We have investigated the individual and combined actions of epidermal growth factor (EGF), transferrin and hydrocortisone on the maturation of whole fetal mouse metanephroi maintained in serum-free conditions for up to 5 days. The presence of EGF (100 ng/ml) resulted in elevated levels of [3H]-thymidine incorporation when compared to controls; autoradiograms showed that the proliferation of mesenchymal cells in the nephrogenic zone is particularly enhanced as verified by cell counting. Brush border hydrolase activities (alkaline phosphatase and gamma-glutamyltransferase), on the other hand, were significantly diminished. Transferrin (5 micrograms/ml) slightly stimulated DNA synthesis and potentiated EGF mitogenic action. The activation of DNA replication by the growth factor seems to be mediated through the protein kinase C pathway. When added alone, hydrocortisone (10(-6) M) strongly inhibited DNA synthesis, stimulated hydrolase activities and exerted a positive effect on brush border differentiation. When combined with EGF or to EGF + transferrin, hydrocortisone counteracted the effects of these latter peptides on DNA synthesis and enzyme activities. Considering the earlier observation of a reciprocal relation between proliferation and differentiation during the neotubulogenic phase of kidney development, the results described in the current study suggest that synergistic and synarchic actions of these heterologous factors are involved in the regulation of tubulogenesis.

Polarized membrane expression of brush‐border hydrolases in primary cultures of kidney proximal tubular cells depends on cell differentiation and is induced by dexamethasone

To analyze the influence of cell differentiation and the effects of hormones on the subcellular distribution of apical antigens in polarized epithelial cells, we have compared the localization of three brush border (BB) hydrolases [neutral endopeptidase (ENDO), aminopeptidase N (APN), and dipeptidylpeptidase IV (DPPIV)] in primary cultures of renal proximal tubule cells grown in various culture media. The degree of cell differentiation modulated by medium composition was estimated by measuring proximal functions, including glucose transport, specific enzymatic activities, and PTH responsiveness. In the dedifferentiated state observed in cells grown in 1% fetal calf serum (FCS)-supplemented medium, the three hydrolases are abnormally concentrated in a cytoplasmic vesicle compartment with weak expression on both membrane domains. By contrast, in serum-free hormonally defined medium (DM: insulin, 5 microgram/ml; dexamethasone, 5 x 10(-8) M), which markedly enhances morphological and functional cell differentiation, the distribution of hydrolases parallels that observed in the normal tubule. When added to the DM devoid of hormones, insulin has little polarizing effect, whereas dexamethasone dramatically increases the apical expression of the hydrolases, which then almost disappear from the basolateral membrane and cytoplasmic vesicular compartments. This glucocorticoid hormone augments the amount of immunoreactive antigen detectable on the apical domain in paraformaldehyde-fixed cells but does not change the total enzymatic activity. This suggests the presence in tubular cells of a dexamethasone-dependent polarizing machinery that requires de novo RNA and protein synthesis, and probably acts mainly by targeting a storage cytoplasmic pool of enzyme to the apical domain.

Effect of Epidermal Growth Factor on the Expression of Digestive Hydrolases in the Jejunum and Colon of Newborn Rats

The regulatory effect of epidermal growth factor (EGF) on the developmental pattern of brush border hydrolases was studied in the proximal jejunum and colon of the newborn rat. In the proximal colon, daily administration of EGF for 1, 3, or 5 days postpartum inhibited the postnatal increase in lactase, maltase, and aminopeptidase specific activities. In contrast, in the jejunum EGF did not influence lactase activity, inconsistently increased maltase activity, and partly prevented the early postnatal decrease in aminopeptidase activity. In the proximal colon, EGF showed additive effects with T4 and hydrocortisone on the inhibition of lactase activity. In the jejunum, EGF potentiated the effect of hydrocortisone and T4 on the expression of sucrase activity and had only a slight effect when injected alone. The incorporation rate of [3H]thymidine in the proximal colon and jejunum was not different in control and treated rats, indicating the absence of an effect of EGF on DNA synthesis. These results show that EGF may play an important physiological role in the enzymatic differentiation of the developing intestine during early postnatal development. Alone or acting with T4 or glucocorticoids, EGF may induce the decline of digestive hydrolases in the proximal colon. In the small intestine EGF may play a major role in the triggering of sucrase expression.

Endocytosis, recycling, and lysosomal delivery of brush border hydrolases in cultured human intestinal epithelial cells (Caco-2).

Lysosomes of intestinal epithelial cells in vivo and in culture display strong immunoreactivity with monoclonal antibodies against various brush border enzymes as visualized by immunoelectron microscopy. Novel subcellular fractionation procedures were developed to study, by the pulse-chase technique and by internalization assays, the pathway along which two microvillar hydrolases, sucrase-isomaltase and dipeptidylpeptidase IV, are transported to lysosomes in the differentiated colon adenocarcinoma cell line Caco-2. 7-9% of metabolically labeled sucrase-isomaltase of dipeptidylpeptidase IV were present in lysosomes after 7-8 h of chase as intact complex-glycosylated molecules. Appearance of these enzymes in lysosomes was biphasic. Endocytosis studies with radioiodinated antienzyme monoclonal antibodies (monovalent antigen-binding fragments) and by means of cell surface iodination revealed only slow transport of the enzymes to lysosomes at a low level. However, both enzymes were internalized with different efficiencies and recycled to the cell surface via endosomes. These results suggest that in Caco-2 cells a significant amount of newly synthesized sucrase-isomaltase and dipeptidylpeptidase IV is directly imported into lysosomes bypassing the brush border membrane.

Isolation and characterization of a small intestinal surfactant-like particle containing alkaline phosphatase and other digestive enzymes

Digestive brush-border enzymes in particulate form have been reported in the intestinal lumen in vivo and in medium from organ explants in vitro. It has been suggested that these particles derive from membrane shedding of the apical brush border. This study describes the isolation and characterization of particles derived from the 105,000 x g supernatant fraction of intestinal luminal washings and from light scrapings of the mucosa itself after fat feeding of rats. These fractions were separated in a continuous NaBr gradient, producing a visible band of 1.07-1.08 g/liter density and resulting in a 15-fold enrichment of intestinal alkaline phosphatase in the band fraction. Other brush-border hydrolases were represented in the banded fraction, but at specific activities only 1/5th to 1/36th that of the brush border. The major phospholipid in the fraction was phosphatidylcholine (58 +/- 15%), containing 75% saturated fatty acids. In contrast, the major brush-border phospholipid was phosphatidyl-ethanolamine. These characteristics showed that the particles derived from the lumen and mucosal surface were not identical to fragments of the brush border. Electron microscopy of the banded fraction revealed partially coiled membrane fragments. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blots, some proteins (e.g. surfactant protein B, collagenous protein 4) were found in common between the intestinal particles and rat pulmonary surfactant. These data suggest the production of a particle secreted by rat intestine that differs from brush-border membranes and that shares some morphological and biochemical similarities with pulmonary surfactant.

Perinatal expression of brush-border hydrolases in rat colon: hormonal and tissue regulations.

The evolution pattern of brush-border digestive hydrolases and their hormonal regulation were studied in the proximal colon of newborn rats. The potentiality of the colon to express a small intestinal enzymatic pattern was also examined in associations made up of colonic endoderm and small intestinal mesenchyme, developed as either intracelomic grafts in 3-day-old chick embryos or as intrarenal grafts in adult rats. A transient increase of lactase- and aminopeptidase-specific activities occurred in the colon from the 19th day of gestation to 14 days after birth, but sucrase activity could never be detected. Immunocytochemical studies with antibodies specific for rat lactase, aminopeptidase, and sucrase confirmed these results. However, the levels of hydrolase activities were lower in the colon than in the jejunum at the same age. Thyroxine or hydrocortisone treatment during the first 4 days postpartum decreased lactase activity by 70 and 30%, respectively, but did not affect aminopeptidase activity. A slight but significant induction of sucrase activity was obtained with both hormones. In contrast, in the jejunum, only thyroxine decreased lactase activity with a lesser effect (30%), but both hormones increased aminopeptidase activity and induced the marked well-known appearance of sucrase activity. The fetal small intestinal mesenchyme was not able to induce the colonic endoderm to achieve a small intestinal-like differentiation. But the exposure of the developed hybrid intestines to glucocorticoids in organ culture allowed expression of sucrase in one-third of the cases. These results demonstrate the presence of brush-border hydrolases in the proximal colon of newborn rats, normally expressed in the small intestine, but never in the adult colon.(ABSTRACT TRUNCATED AT 250 WORDS)

Maintenance of proximal and distal cell functions in SV40‐transformed tubular cell lines derived from rabbit kidney cortex

This paper reports the preparation and describes the properties of three renal tubular cell lines derived using SV40 infection of primary cultures of rabbit kidney cortical cells, enriched in proximal cells. RC.SV1 was initially derived from cultures grown in the presence of fetal calf serum exhibiting a low degree of proximal differentiation. The cells were subsequently adapted to grow in serum-free hormonally defined medium and display basic properties of proximal tubule cells including well-developed apical microvilli, strong expression of brush-border hydrolases, Na+-coupled glucose uptake, and increased cyclic AMP production when exposed to PTH. The other two cell lines were derived from cultures in serum-free hormonally defined medium and propagated in the same medium. They are characterized by some common properties including rare and short microvilli, low expression of apical hydrolases, and low or undetectable Na+-dependent glucose uptake, but differ by their abilities to respond by an increase in cAMP to various hormonal stimuli. RC.SV2 cells are sensitive to calcitonin and to a lesser extent to isoproterenol and PTH, suggesting that they may originate from the thick ascending limb of Henle's loop and the bright portion of the distal tubule. RC.SV3 responds essentially to isoproterenol and arginine vasopressin, suggesting a more distal origin (late distal and initial collecting tubule). Emergence of distal cell lines from cultures exhibiting proximal characteristics may be related to distal cell overgrowth as suggested by analysis of growth kinetics and increased Na+/H+ exchanger activity in RC.SV2 compared with RC.SV1.

Asynchronous Transport to the Cell Surface of Intestinal Brush Border Hydrolases Is Not Due to Differential Trimming of N-Linked Oligosaccharides

Intestinal brush border enzyme glycoproteins are transported to the microvillar membrane at different rates in the differentiated intestinal cell line Caco-2. This asynchronism is due to at least two rate-limiting events, a pre- and an intra-Golgi step (Stieger B., Matter, K., Baur, B., Bucher, K., Höchli, M., and Hauri, H.P. (1988) J. Cell Biol. 106, 1853-1861). A possible cause for the asynchronous protein transport might be differential trimming of N-linked oligosaccharide side chains. The effects of two trimming inhibitors on the intracellular transport of sucrase-isomaltase, a slowly migrating hydrolase, and dipeptidylpeptidase IV, a rapidly migrating hydrolase, are described. 1-Deoxymannojirimycin, an inhibitor of Golgi alpha-mannosidase I, had no influence on the rate of appearance of these hydrolases in the brush border membrane as assessed by subcellular fractionation. In the presence of N-methyl-1-deoxynojirimycin, an inhibitor of glucosidase I, 30-40% of the newly synthesized molecules appeared at the cell surface, and half-time for appearance of this pool was identical to that found in control cells. The reduced maximal transport to the cell surface observed with N-methyl-1-deoxynojirimycin may suggest that proper glycosylation is necessary for an efficient transport from the Golgi apparatus to the microvillar membrane. Inhibition of glucosidase I does not prevent the acquisition of endoglycosidase H resistance. Furthermore, evidence is presented that the processing in the presence of N-methyl-1-deoxynojirimycin leads to glycosylated endoglycosidase H-resistant glycoproteins.

Imbalance between Jejunum and Ileum in the Response of Brush Border Hydrolases to Oral Feeding after Intravenous Alimentation in Rats

The effect of oral refeeding after total parenteral nutrition (TPN) on brush border hydrolases was measured in the proximal jejunum and ileum of adult rats. The animals received intravenously for 4 days a mixture of Intralipid 10% and Vamine-Glucose. At the end of TPN, oral feeding was reinstituted and the rats were fed with an isocaloric standard diet (60% carbohydrate, 17% protein, 3% lipid). Sucrase, isomaltase, lactase, and aminopeptidase N activities were measured at the end of TPN and at 1, 3, and 5 days after TPN. Sham-operated rats nourished orally with the standard diet were used as controls. In both intestinal segments, lactase activity showed no significant changes at the end of TPN or during oral realimentation. Isomaltase, and especially sucrase activities, exhibited an important drop at the end of TPN. After TPN, a complete restoration of isomaltase and sucrase activities was obtained in the jejunum only. During oral refeeding a 40% deficit in sucrase activity persisted in the ileum throughout the experimental period, whereas normal isomaltase activity was restored in this segment. Aminopeptidase N activity was lowered by TPN and recovered normal values within a few hours after oral realimentation. Thus, reinstitution of oral feeding after TPN should take into account that the intestine is capable of digesting normal amounts of dietary protein but has a reduced tolerance for carbohydrates.

Age related increase of brush border enzyme activities along the small intestine.

Intestinal morphology and brush border hydrolase activities were determined along the small intestine of young adult (three months, n = 10), mature (12 months, n = 10), and senescent (29 months, n = 15) rats. The intestinal segments of the senescent rats contained higher mucosal mass and protein content (p less than 0.05) compared with the young and mature animals. A significant reduction of villus height and crypt depth (p less than 0.05) was found in the proximal intestine during aging. A 35% increase in villus height (p less than 0.05) without changes in crypt depth, was observed in the distal ileum in senescent rats. The activities of sucrase and isomaltase were significantly increased during aging in the duodenum and jejunum (p less than 0.05). Lactase and aminopeptidase activities which showed only minor changes between young and mature animals were significantly enhanced in senescent animals (p less than 0.05) with aminopeptidase exhibiting a three-fold increase in activity in the proximal ileum. The results when combined with those of previous studies suggest that in the aged animal, the increased level of intestinal hydrolase activities may be the consequence of prolonged cellular maturation along the villi in the proximal intestine, and of adaptation to increased concentrations of intraluminal substrates in the distal intestine.

Neutral maltase of human granulocytes: Localization on the extracytoplasmic side of the plasma membrane and some properties

Neutral maltase is an alpha-glucosidase (alpha-D-glucoside glucohydrolase, EC 3.2.1.20) which is present in human granulocytes and B-lymphocytes but not in T-lymphocytes. These cells have been reported to contain a renal-type neutral maltase which cross-reacts with an antiserum raised against kidney brush-border enzyme. No study has been performed to assess the subcellular localization of the enzyme. Molecular properties of leukocyte neutral maltase from any species are unknown. We report in this paper that neutral maltase is present on the extracytoplasmic side of human granulocyte plasma membrane. These results are supported by subcellular fractionation on Percoll gradient and by papain digestion of intact granulocytes. The enzyme is probably an integral membrane protein. The anchorage to the lipid bilayer may be similar to that of the stalked brush-border hydrolases. Some properties of granulocyte neutral maltase were also determined on a plasma membrane-enriched fraction. The enzyme cleaves maltose and nigerose but not other glucosides disaccharides and oligosaccharides. The Km for maltose is (+/- SD) 0.78 (+/- 0.06) mM, that for nigerose 21.05 (+/- 1.43) mM. The Vmax for nigerose is 0.83-fold that for maltose. Tris, maltotriose, maltotetraose, and maltopentaose were inhibitors of granulocyte neutral maltase.

Characterization of monoclonal antibodies specific for rabbit renal brush-border hydrolases: application to immunohistological localization.

By use of immunodepletion studies, we characterized four monoclonal antibodies reactive with rabbit brush-border (BB) as specific for aminopeptidase N (AP), dipeptidylpeptidase IV (DPPIV), neutral endopeptidase (EP), and angiotensin-converting enzyme (ACE), and we used these antibodies for immunohistochemical detection of these four hydrolases. Expression within the kidney was studied by light and electron microscopy. All four hydrolases are expressed on the various segments of the proximal tubule. In addition, EP and DPPIV are detectable on visceral epithelial cells of the glomerulus and AP on the cells of Bowman's capsule. Outside the kidney, the four hydrolases are expressed within the digestive and genital tracts, where AP, EP, and DPPIV predominate on epithelial structures, whereas ACE is essentially located in vascular structures. The latter localization is also characteristic of ACE in the other organs studied, where clear-cut systematic distribution of the other hydrolases was often difficult to demonstrate. In addition, AP, DPPIV, and EP were detected on lymphoid cells. As compared to reports of data obtained essentially by enzymatic or immunoradiometric assays, these observations suggest considerable interspecies variations of extrarenal expression of the major BB hydrolases. This should be taken into account in attempting to define a general physiological role for a given enzyme.

Selective effects of PHA on rat brush border hydrolases along the crypt-villus axis.

The mechanism of the toxicity of lectin from Phaseolus vulgaris seeds has been investigated on rat enterocytes. Cell isolation procedures showed a selectivity in the loss of brush border hydrolases; this indicated that the microvilli blebbing was not the only mechanism of action of lectins on rat enterocytes.

Human colon cell line HT-29: Characterisation of 1,25-dihydroxyvitamin D 3 receptor and induction of differentiation by the hormone

The human colon carcinoma cell line HT-29 differentiates into functional enterocytes upon replacement of glucose by galactose in the culture medium. Since the differentiation of other types of cells is associated with the modulation of 1,25-dihydroxycholecalciferol (1,25(OH) 2D 3) receptor concentrations and since enterocytes are classical target cells for 1,25(OH) 2D 3 we have examined the HT-29 cells to determine whether the differentiated and undifferentiated stages could be directly linked to the presence of 1,25(OH) 2D 3 receptors. HT-29 cells were grown in Dulbecco's modified medium containing 10% fetal calf serum (FCS) and glucose or galactose. Cell differentiation was assessed by measuring the brush border hydrolase, maltase. 1,25(OH) 2D 3 receptors were studied in the cells after 48 h without FCS. Nuclear uptake was measured in intact dispersed cells and the receptor protein was further characterized by vitamin D metabolite binding specificity, sucrose density gradient analysis and binding to DNA-cellulose. Maltase activity was 5-fold greater in differentiated HT-29 cells than in undifferentiated cells. Scatchard analysis showed a highly specific saturable (9500 sites per cell) high affinity (2 × 10 −10 M), binding of 1,25(OH) 2D 3 in undifferentiated cells. This receptor-like protein sedimented at 3.3S, bound to and eluted from DNA-cellulose and had all the characteristics of a 1,25(OH) 2D 3 receptor. No specific binding was detected in differentiated HT-29 cells. The presence of 1,25(OH) 2D 3 receptors in undifferentiated HT-29 cells implies that these cells are targets for vitamin D. The maltase activity increased significantly when undifferentiated cells were exposed to 1,25(OH) 2D 3 for 5–6 days, indicating that the hormone can promote differentiation of HT-29 cells. These results demonstrate that HT-29 cells can provide a new model for studying steroid receptor regulation and cell differentiation.

Selective alteration of brush-border hydrolases in intestinal diseases in childhood.

1. Biochemical estimates of lactase, sucrase and maltase activities, carried out on intestinal biopsies appearing histologically normal, were compared with those obtained from children suffering from coeliac disease, cow's milk protein intolerance/postenteritis syndrome and the intractable diarrhoea syndrome of infancy. Lactase deficiency in these children was found to be more pronounced than sucrase or maltase deficiencies. 2. Quantitative cytochemical investigations showed characteristic disease-induced changes in the ability of enterocytes to express alpha- and beta-glucosidases, but not alkaline phosphatase activities, during migration along stunted villi. 3. Separate estimates of the time course describing hydrolase development in normal and coeliac tissue showed the initial rate of lactase appearance to be halved in coeliac patients, while that for alpha-glucosidases remained constant and that for alkaline phosphatase increased by a factor of four. Enteroblastic replacement of mature enterocytes cannot provide a general explanation for hydrolase deficiency in diseased intestine.

Enhancement of maternal and fetal nephrotoxicity of salicylate by zinc deficiency. Morphological, enzyme histochemical and immunohistochemical studies.

An oral dose of 700 mg/kg salicylic acid was given to normal and Zn-deficient rats at day 16 of gestation. Maternal and fetal kidneys were studied at day 19 of gestation. Zn-deficiency did not cause any lesions detectable by semi-thin section light microscopy, electron microscopy, enzyme histochemistry and immunohistochemistry. Salicylate may lead only to small morphological, enzymatic and cytoskeletal defects in the maternal and fetal kidney. However, enzyme activities decreased in plasma membranes, mitochondria, lysosomes, endoplasmic reticulum and peroxisomes in all segments of the tubular apparatus when salicylate was given to Zn-deficient rats. Cytoskeletal proteins such as keratin in the glomerular cells and epithelial lining of the collecting ducts and vimentin in vascular endothelial cells of the maternal kidney were also affected. In addition, the epithelial cells of the collecting ducts, which were comparatively less damaged, accumulated high amounts of fat. In severe cases, the enzymatic and cytoskeletal lesions were accompanied by hematuria and tubular necroses including and collecting ducts in the renal papilla. In less severe cases reduced activities of brush border hydrolases were the only sign of disturbed renal function in maternal rats indicating that membrane alteration and loss of membrane-bound enzymes are the primary defects. In the fetal kidneys, mitotic activity of the cells of the nephron anlagen and collecting ducts was reduced and enzymatic and morphological differentiation were disturbed. As a consequence less mature nephrons and collecting ducts occurred.

Comparison between mouse kidneys of pre- and postnatal ages maturing In vivo and in serum-free organ culture

1. 1. To evaluate the influence of age, DNA synthesis and brush border hydrolase activites were determined in mouse kidneys maturing in vivo and in serum-free organ culture. 2. 2. DNA synthesis decreased with advancing age. 3. 3. The protein content and leucylnaphthylamidase, maltase, trehalase, alkaline phosphatase and γ-glutamyltransferase activities increased with aging. 4. 4. The differences due to age were reproduced in kidneys maturing in culture. 5. 5. These results show that age has a significant effect on the parameters determined, but apparently has no influence on the viability of the kidney explants in culture.

Villin, intestinal brush border hydrolases and keratin polypeptides in intestinal metaplasia and gastric cancer; an immunohistologic study emphasizing the different degrees of intestinal and gastric differentiation in signet ring cell carcinomas

Gastric carcinomas have been assayed for the presence of villin and for the small intestinal hydrolases aminopeptidase N and sucrase isomaltase. These proteins seem not to be present in normal stomach epithelium. However intestinal metaplasia in stomach, and tumour cells in the glandular patterns of gastric carcinoma were positive for all three markers, showing characteristic apical positivity. In contrast, in diffuse gastric carcinomas the percentage of signet ring cells positive for these markers varied from 10-100% with each marker showing a similar percentage of positive cells. Testing of gastric carcinomas with antibodies specific for different keratin polypeptides showed that while all 7 tumours were positive for keratins 8 and 18.2 were also positive for keratin 7. In the keratin 7 positive tumours all tumour cells were keratin 7 positive. The keratin 8 antibody also reacted on routinely fixed specimens. Thus gastric carcinomas reveal different degrees of gastric and intestinal differentiation.

EFFECTS OF HYDROCORTISONE ON HUMAN FOETAL KIDNEY IN SERUM-FREE ORGAN CULTURE

The influence of hydrocortisone (HC) on the in vitro maturation of human foetal kidney was studied. Following legal therapeutic abortions, explants (2 × 2 mm) of renal cortex from foetuses aged 12-18 weeks, were placed on a lens paper covering a stainless steel grid lying over the central well of a Falcon culture dish. The explants were cultured for 2 and 5 days in serum-free Leibovitz L-15 medium at 37°C in a mixture of 95% air-5% CO2, without hormones (controls) or with HC at concentrations of 12.5, 25 or 50 ng/ml. During the studied period, the overall architecture of the renal structures was preserved without evident signs of nephrogenesis. DNA synthesis was measured by incorporation of 3H-thymidine and was increased on day 5 by 80% with the addition of HC at 12.5 ng/ml and by 131% with 50 ng/ml. The sites of 3H-TdR incorporation were the same after HC addition. The activity of some brush border hydrolases was modified by HC. Gamma-glutamyltranspeptidase activity was reduced by 68% on day 2 and by 42% on day 5 with 12.5 ng of HC. Maltase activity was increased by 19% on day 2 with 50 ng of the hormone. Trehalase activity was reduced by 61% with 12.5 ng and by 50% with 50 ng of HC, on day 5. Alkaline phosphatase activity was decreased on day 2, by 50% with 12.5 ng and by 39% with 25 and 50 ng of HC. This study provides for the first time, basic data on the direct effects of hydrocortisone on proliferation and brush border enzyme activities in the human foetal kidney maintained in organ culture. (MRC of Canada)