Similar developmental patterns in immunolocalisation of stem cell factor and KIT in bovine meso- and metanephros

The mesonephros is often regarded as a simplified version of the terminal renal organ, the metanephros. Both renal organs result from an epithelio-mesenchymal interaction between the Wolffian duct and the nephrogenic ridge. It appears that the epithelio-mesenchymal interaction makes use of similar signal cascades for both renal organs and that key events required for the development of the metanephros occur at earlier stages. In murine metanephroi, the stem cell factor (SCF)/-KIT-signal transduction pathway has recently been shown to regulate ureteric bud branching and epithelial cell differentiation. We immunohistochemically defined the time-sequence of KIT and SCF presence in both renal organs using bovine embryos/foetuses with crown rump length (CRL) of 1.7–24 cm. In the mesonephroi, epithelial cells with strong KIT staining were scattered in distal tubules, and SCF was expressed in the epithelial wall of corpuscles and proximal tubules. KIT positivity occurred in the metanephroi of embryos prior to SCF; KIT was predominantly localised at the ureteric bud tips in the nephrogenic zone. In foetuses of 13 cm and more CRL, the SCF/KIT profile of developmentally advanced nephrons mirrored the situation in the mesonephros. Epithelial cells with strong KIT staining were scattered in the cortical areas of distal tubules, while SCF was expressed in the epithelial wall of corpuscles and proximal tubules. Our morphological findings agree with a potential role of KIT at the ureteric bud tips and demonstrate a similar expression of KIT and SCF along the areas of developmentally advanced mesonephric and metanephric nephrons.     

The distribution of dopamine-like immunoreactivity in the thoracic and abdominal ganglia of the locust (Schistocerca gregaria)

Summary An indirect gold-labeling method utilizing the lectin from Limax flavus was employed to characterize the subcellular distribution of sialic acid in glycoconjugages of the salamander olfactory mucosa. The highest density of lectin binding sites was in secretory vesicles of sustentacular cells. Significantly lower densities of lectin binding sites were found in secretory granules of acinar cells of both Bowman's and respiratory glands. Lectin binding in acinar cells of Bowman's glands was confined primarily to electron-lucent regions and membranes of secretory granules. In the olfactory mucus, the density of lectin binding sites was greater in the region of mucus closest to the nasal cavity than in that closest to the epithelial surface. At the epithelial surface, the density of lectin binding sites associated with olfactory cilia was 2.4-fold greater than that associated with microvilli of sustentacular cells or non-ciliary plasma membranes of olfactory receptor neurons, and 7.9-fold greater than non-microvillar sustentacular cell plasma membranes. Lectin binding sites were primarily associated with the glycocalyx of olfactory receptor cilia. The cilia on cells in the respiratory epithelium contained few lectin binding sites. Thus, sialylated glycoconjugates secreted by sustentacular cells are preferentially localized in the glycocalyx of the cilia of olfactory receptor neurons.     

Angiotensin II binding to tissues of the rainbow trout,Oncorhynchus mykiss,studied by autoradiography

Summary Tissue slices from seawater-adapted and freshwater-adapted rainbow trout, Oncorhynchus mykiss, were exposed to ¹²⁵I-angiotensin II (1.01·10^-9 M) and binding sites located by light-microscopic autoradiography. Binding/uptake was significantly inhibited by excess (10^-5 M) unlabelled angiotensin II, suggesting specific binding/uptake of angiotensin II to the ventral and dorsal aorta (smooth muscle), urinary bladder (smooth muscle and epithelial lining), glomeruli and proximal tubules, the gill (lamellae and central filament), skin (epithelium), intestine and oesophagus (mucosal epithelium), liver, heart (ventricular myocytes), adrenocortical tissue and brain (cerebellum and medulla oblongata). The specific binding/uptake of angiotensin II to tissues of freshwater- and seawater-adapted animals were generally similar. However, binding/uptake by the proximal tubules was significantly higher in freshwater-adapted trout than seawater-adapted trout. Specific binding/uptake of angiotensin II by the smooth muscle of the bladder was significantly higher in trout adapted to seawater than trout adapted to freshwater.     

Binding sites of Ulex europaeus-lectin I in human parotid gland

Summary Twenty non-neoplastic parotid glands (removed during neck dissection for regional tumours) were examined for cellular and subcellular binding sites of Ulex europaeus-lectin I (UEA-I), a lectin reported to be specific for -L-fucose. For light microscopy, an extended peroxidase-antiperoxidase method was applied; for the evaluation of the subcellular localization of bound lectin, three of these glands were examined following immunocryoultramicrotomy and staining by the protein A-gold technique.In addition to the known cytoplasmic affinity of UEA-I for capillary endothelium, acinar cells bound the lectin within the cytoplasmic compartment; the number and distribution of stained acinar cells varied among individuals. Furthermore, cytomembrane-bound labelling that occurred most markedly at the luminar surface was observed in striated-duct epithelium.Using the electron microscope, protein A-gold particles were seen in zymogen granules and in Golgi cisternae of serous acinar cells; primary saliva secreted in the lumina exhibited strong labelling; serous acinar cells had binding sites on their cell membranes, striated-duct epithelium had binding sites on its surface membrane and in the vicinity of apical vesicles. Our results show that UEA-I is a useful tool for the study of the structure and functional states of the parotid gland epithelium and its associated pathological alterations.Dedicated to Prof. Dr. med. G. Seifert on the occasion of his 65th birthday     

Characteristics of the compensatory renal growth of the remnant embryonic chick kidneys

Growth of the remnant embryonic kidney (the mesonephros), as expressed by wet weight, was more rapid in the chick embryos with experimentally induced unilateral renal agenesis compared to controls. The difference was significant between embryonic days 8-12, when the doubled weights of remnant kidneys were increased compared with the weights of paired control kidneys. The excessive growth of the mesonephros ceased on day 14, when the normal physiological regression of the embryonic kidney begins. In the definitive kidney, the metanephros, no significant differences in weights of the control vs. remnant metanephros were found on days 10-14. The characteristics of increased mesonephric growth were evaluated by determination of DNA/protein ratios in homogenates of the kidneys. Significant cellular hypertrophy was found in both the mesonephros and metanephros of the embryos with URA on day 10. Additionally, a non-significant cellular hyperplasia was also revealed in the remnant mesonephros on day 8. This gives evidence that the growth stimuli to the mesonephroi were probably strongest between days 8-10 and that they manifested in the remnant mesonephros only.     

The Heat-Stable Enterotoxin-Guanylin Receptor is Expressed in Rat Hepatocytes and in a Rat Hepatoma (H-35) Cell Line

Abstract

Background/Aims: Guanylyl cyclase C (GC-C) is an intestinal transmembrane receptor which binds both guanylin, an endogenous ligand, and Escherichia coli heat-stable enterotoxin (STa) resulting in 5′-cyclic guanosine monophosphate (cGMP) accumulation and chloride secretion. In the adult rat, there is a high basal level of GC-C expression in the intestine, but not in the liver. Increased expression of GC-C in the rat liver has been demonstrated during the perinatal period as well as with liver regeneration and during an acute phase response. The aim of this study was to identify and utilize cell culture models to further characterize the expression of GC-C in the liver. Methods: STa binding, STa-stimulated cGMP accumulation, and GC-C RNA expression by Northern analysis were determined in primary cultures of rat hepatocytes and H-35 cells, a rat hepatoma cell line, following treatment with dexamethasone and/or interleukin-6 (IL-6). Results: In rat hepatocytes treated with the combination of dexamethasone and IL-6, there was an increase in STa binding, STa-stimulated cGMP accumulation, and GC-C RNA expression as compared to untreated cells. In H-35 cells treated with dexamethasone alone, there was an increase in STa binding, STa-stimulated cGMP accumulation, and GC-C RNA expression as compared to untreated cells. Conclusion: Primary cultures of rat hepatocytes and H-35 cells can be utilized to further study upregulation of GC-C in the hepatocyte. The expression of this receptor in hepatocytes, combined with the recent demonstration of circulating guanylin, is consistent with a functional role for GC-C in the liver.     

Immunocytochemical localization of a vacuolar-type ATPase in Malpighian tubules of the ant Formica polyctena

The presence of a vacuolar-type ATPase in Malpighian tubules of the ant Formica polyctena was investigated immunocytochemically, using antibodies to vacuolar ATPases of Manduca sexta midgut and bovine kidney. Specific labelling was observed at the brush border of the epithelium extending along the entire length of the tubules. These findings agree with the current view that a vacuolar ATPase is situated at the apical membrane of Malpighian tubule cells and other insect epithelial cells, being the energizing element of an electrogenic potassium pump. When antibodies were tested on tubules in different secretion conditions prior to fixation, no differences were observed in the distribution of the vacuolar ATPase.This work was supported by grants from the European Community (SCI-CT90-0480), from the Ministerio de Educación y Ciencia DGICYT, Spain (CE 91-0002), and from the Deutsche Forschungsgemeinschaft (Wi 698-3).     

人源产肠毒素大肠杆菌疫苗的研发进展

腹泻是全球范围内引起5岁以下幼童死亡的第二大病因,而产肠毒素大肠杆菌(ETEC)是引起腹泻的最常见病原菌,其产生的细菌定植因子(CFs)和肠毒素是关键的毒力因子。CFs介导细菌黏附宿主小肠上皮细胞并完成定植,产生热敏肠毒素(LT)和热稳定肠毒素(ST)破坏宿主上皮细胞内的体液平衡,使体液和电介质过量分泌从而导致腹泻。预防ETEC腹泻的首选方法是使用能激发宿主产生抗黏附素免疫力和抗肠毒素免疫力的疫苗,阻断ETEC黏附和定植并中和肠毒素。目前一种名为Dukoral~的霍乱疫苗因能刺激机体产生抗热敏毒素免疫,已经被一些国家批准用于短期保护和预防旅行者腹泻。新型试验性ETEC候选疫苗正在研发中,旨在提供保护期长、反应谱广的抗ETEC感染免疫保护力。本文针对疫苗研发的关键问题和研究现状作一综述,并对未来的研究作出展望。     

Two distinct origins for Leydig cell progenitors in the fetal testis

During the differentiation of the mammalian embryonic testis, two compartments are defined: the testis cords and the interstitium. The testis cords give rise to the adult seminiferous tubules, whereas steroidogenic Leydig cells and other less well characterized cell types differentiate in the interstitium (the space between testis cords). Although the process of testis cord formation is essential for male development, it is not entirely understood. It has been viewed as a Sertoli-cell driven process, but growing evidence suggests that interstitial cells play an essential role during testis formation. However, little is known about the origin of the interstitium or the molecular and cellular diversity within this early stromal compartment. To better understand the process of mammalian gonad differentiation, we have undertaken an analysis of developing interstitial/stromal cells in the early mouse testis and ovary. We have discovered molecular heterogeneity in the interstitium and have characterized new markers of distinct cell types in the gonad: MAFB, C-MAF, and VCAM1. Our results show that at least two distinct progenitor lineages give rise to the interstitial/stromal compartment of the gonad: the coelomic epithelium and specialized cells along the gonad–mesonephros border. We demonstrate that both these populations give rise to interstitial precursors that can differentiate into fetal Leydig cells. Our analysis also reveals that perivascular cells migrate into the gonad from the mesonephric border along with endothelial cells and that these vessel-associated cells likely represent an interstitial precursor lineage. This study highlights the cellular diversity of the interstitial cell population and suggests that complex cell–cell interactions among cells in the interstitium are involved in testis morphogenesis.     

Expression of apoptosis-associated speck-like protein containing a caspase recruitment domain, a pyrin N-terminal homology domain-containing protein, in normal human tissues.

Apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) is a pyrin N-terminal homology domain (PYD)- and caspase recruitment domain (CARD)-containing a proapoptotic molecule. This molecule has also been identified as a target of methylation-induced silencing (TMS)-1. We cloned the ASC cDNA by immunoscreening using an anti-ASC monoclonal antibody. In this study, we determined the binding site of the anti-ASC monoclonal antibody on ASC and analyzed the expression of ASC in normal human tissues. ASC expression was observed in anterior horn cells of the spinal cord, trophoblasts of the placental villi, tubule epithelium of the kidney, seminiferous tubules and Leydig cells of the testis, hepatocytes and interlobular bile ducts of the liver, squamous epithelial cells of the tonsil and skin, hair follicle, sebaceous and eccrine glands of the skin, and peripheral blood leukocytes. In the colon, ASC was detected in mature epithelial cells facing the luminal side rather than immature cells located deeper in the crypts. These observations indicate that high levels of ASC are abundantly expressed in epithelial cells and leukocytes, which are involved in host defense against external pathogens and in well-differentiated cells, the proliferation of which is regulated.     

Differential tissue distribution of the Invs gene product inversin

Nephronophthisis is a common genetic cause of end-stage renal disease in childhood. Recently, Invs was identified as the gene mutated in the infantile form of nephronophthisis. Humans with nephronophthisis develop a large number of extrarenal manifestations, including situs variations, anomalies of the hepatobiliary system, retinal degeneration and cerebellar ataxia. Mice homozygous for a mutation in the Invs gene (inv mouse) die during the first week after birth as a result of renal and liver failure. Although organ anomalies have been characterized in human nephronophthisis and the inv mouse, little is known about the tissue expression of the Invs gene product, inversin. We have used laser confocal microscopy of paraffin-embedded murine tissue sections to provide the first detailed characterization of the distribution of inversin in various organs. Our results show that inversin is localized to distal tubules in the kidney, hepatic bile ducts, acinar and ductal pancreatic cells, epithelial intestinal cells, splenic germinal centres, bronchiolar epithelial cells, dendrites of cerebellar Purkinje cells, retinal neural cells and spermatocytes and spermatids in the testis. The localization of inversin in distal tubules in the kidney and in extrarenal tissues suggests that the expression of this protein has an important function in a variety of organs. Further studies are required to understand the way in which mutations in the Invs gene lead to the multi-organ pathology of inv mouse and human nephronophthisis. J.N. acknowledges funding from the Deutsche Forschungsgemeinschaft (Nu 118/1-1, Nu 118/3-1) and the intramural research program of the University Hospital of Essen (IFORES). A. K. acknowledges funding from the Deutsche Forschungsgemeinschaft (Kr 1108/2-2).     

Comparative immunohistochemical analysis of the expression of cytokeratins, vimentin and alpha-smooth muscle actin in human foetal mesonephros and metanephros

The human mesonephros is currently regarded as a simplified version of the foetal metanephros, primarily due to the close morphological resemblance between these two structures. The aim of the present study was to define whether human mesonephric and foetal metanephric nephrons share immunophenotypical traits in their corresponding structures (glomeruli, proximal and distal tubules). For this purpose we first investigated immunohistochemically the overall expression and topographical distribution of cytokeratins 7, 8, 18, 19, and 20, vimentin and -smooth muscle actin in mature mesonephric nephrons and compared the results with those obtained in maturing-stage foetal metanephric nephrons. No expression of cytokeratins 7 and 20 was found. Cytokeratins 8, 18, and 19 and vimentin showed a restricted and basically coincident expression along the different components of both mesonephric and metanephric nephrons. These findings indicate that the intermediate filament protein profile of human mature mesonephric nephrons closely recapitulates that observed in developing metanephros and thereby strengthens the concept that human mesonephros, a transient ontogenic structure, is largely similar to the foetal metanephros.The sole difference between human mesonephros and foetal metanephros was the divergent expression of -smooth muscle actin. This protein exhibited an increasingly accentuated mesangial expression paralleling the morphological maturation of metanephric glomerulus, whereas it was absent from the mesonephric one. This would suggest that the mesangial cells in these two renal structures have a different function during the foetal life.     

Expression of intermediate filaments,EGF and TGF-α in early human kidney development

The spatial and temporal expression patterns of cytokeratins, vimentin, epithelial growth factor (EGF) and transforming growth factor alpha (TGF-α), were investigated in the 5–9-week old human mesonephros and metanephros. Vimentin was found in all mesonephric structures, while cytokeratins were seen only in the mesonephric tubules. EGF and TGF-α were detected early in all mesonephric structures, and immunoreactivity to both factors decreased in later stages. In the 5–6-week metanephros, vimentin immunoreactivity was found in all structures and later increased in the collecting system and interstitium. In the 5th week, cytokeratins 8 and 19 appeared in the ureteric bud and ampullae, and later showed increasing immunoreactivity in the collecting system and nephrons. The coexpression of intermediate filament proteins in metanephric development is a temporary feature and might be associated with mesenchymal to epithelial transformation of developing nephrons. In adult kidneys, such coexpression is associated with fibrosis or carcinomatous changes. At early stages, immunoreactivity to EGF and TGF-α was detected in all metanephric structures and from the 7th week onward, it decreased in differentiating nephrons. EGF and TGF-α patterns of appearance indicate their role in induction, proliferation and growth of metanephric structures. Disturbances in that pattern might cause reduction in kidney growth.     

Lectin activity and distribution of chicken lactose lectin I in the extracellular matrix of the chick developing kidney

A lectin activity inhibitable by thiodigalactose, N-acetyllactosamine, lactulose, lactose and by an antibody raised against CLL I (chicken-lactose lectin I) has been investigated in the chick embryo developing kidney. At post-induction stages this activity was found in both mesonephros and metanephros. In immunofluorescence and immunoelectron microscopy, the extracellular distribution of CLL I was similar in the mesonephros and the metanephros. The lectin was never found intracellularly; cultured kidney cells did not express any endogenous lectin but were rich in lectin-receptor sites, which led to the hyphothesis that CLL I is not produced in situ but could be adsorbed on renal cells. Potential physiological roles for embryonic lectins are discussed.     

Comparison of the glycolipid-binding specificities of cholera toxin and porcineEscherichia coli heat-labile enterotoxin: identification of a receptor-active non-ganglioside glycolipid for the heat-labile toxin in infant rabbit small intestine

The binding specificities of cholera toxin andEscherichia coli heat-labile enterotoxin were investigated by binding of¹²⁵I-labelled toxins to reference glycosphingolipids separated on thin-layer chromatograms and coated in microtitre wells. The binding of cholera toxin was restricted to the GM1 ganglioside. The heat-labile toxin showed the highest affinity for GM1 but also bound, though less strongly, to the GM2, GD2 and GD1b gangliosides and to the non-acid glycosphingolipids gangliotetraosylceramide and lactoneotetraosylceramide. The infant rabbit small intestine, a model system for diarrhoea induced by the toxins, was shown to contain two receptor-active glycosphingolipids for the heat-labile toxin, GM1 ganglioside and lactoneotetraosylceramide, whereas only the GM1 ganglioside was receptor-active for cholera toxin. Preliminary evidence was obtained, indicating that epithelial cells of human small intestine also contain lactoneotetraosylceramide and similar sequences. By computer-based molecular modelling, lactoneotetraosylceramide was docked into the active site of the heat-labile toxin, using the known crystal structure of the toxin in complex with lactose. Interactions which may explain the relatively high toxin affinity for this receptor were found.Abbreviations CT cholera toxin - CT-B B-subunits of cholera toxin - LT Escherichia coli heat-labile enterotoxin - hLT humanEscherichia coli heat-labile enterotoxin - pLT porcineEscherichia coli heat-labile enterotoxin - EI electron ionization     

Essential function of Wnt-4 for tubulogenesis in the Xenopus pronephric kidney

In the vertebrate embryo, development of the excretory system is characterized by the successive formation of three distinct kidneys: the pronephros, mesonephros, and metanephros. While tubulogenesis in the metanephric kidney is critically dependent on the signaling molecule Wnt-4, it is unknown whether Wnt signaling is equally required for the formation of renal epithelia in the other embryonic kidney forms. We therefore investigated the expression of Wnt genes during the pronephric kidney development in Xenopus. Wnt4 was found to be associated with developing pronephric tubules, but was absent from the pronephric duct. Onset of pronephric Wnt-4 expression coincided with mesenchyme-to-epithelium transformation. To investigate Wnt-4 gene function, we performed gain- and loss-of-function experiments. Misexpression of Wnt4 in the intermediate and lateral mesoderm caused abnormal morphogenesis of the pronephric tubules, but was not sufficient to initiate ectopic tubule formation. We used a morpholino antisense oligonucleotide-based gene knockdown strategy to disrupt Wnt-4 gene function. Xenopus embryos injected with antisense Wnt-4 morpholinos developed normally, but marker gene and morphological analysis revealed a complete absence of pronephric tubules. Pronephric duct development was largely unaffected, indicating that ductogenesis may occur normally in the absence of pronephric tubules. Our results show that, as in the metanephric kidney, Wnt-4 is critically required for tubulogenesis in the pronephric kidney, indicating that a common, evolutionary conserved gene regulatory network may control tubulogenesis in different vertebrate excretory organs.     

Functional vasoactive intestinal polypeptide (VIP)-system in salt glands of the Pekin duck

Summary In saltwater-acclimated ducks with fully specialized supraorbital salt glands, intracarotid application of acetylcholine (5 nmoles/min/kg b.w.) or porcine vasoactive intestinal polypeptide (pVIP) (240 pmoles/min/kg b.w.) induced secretion from the salt glands at threshold conditions of secretory activity. pVIP-like immunoreactivity could be localized in fibers of the postganglionic secretory nerve ramifying throughout the glandular parenchyma. Both middle-sized arterioles and secretory tubules were innervated, and pVIP-immunoreactive varicose fibers formed peritubular baskets around the basal region of secretory tubules indicating direct innervation of the secretory tissue. pVIP-specific staining could be abolished by preabsorption of the antiserum with peptide extracts of salt-gland tissue. Synthetic pVIP and endogenous VIP from salt glands of the duck co-eluted on the HPLC system, suggesting structural similarity of the peptides. Membrane-binding studies with radioiodinated pVIP revealed the presence of high-affinity binding sites in salt-gland tissue. Affinities of unlabeled pVIP analogues to compete for these binding sites were as follows: pVIP > PHI > pVIP antagonist > secretin > pVIP (10–28) > chicken VIP (16–28). Peptide extracts of salt glands had affinities similar to pVIP. Binding sites could be localized mainly at the apical end of the radially arranged secretory tubules, as demonstrated by receptor autoradiography.It is concluded that, in addition to the classical parasympathetic transmitter acetycholine, VIP serves as neuromodulator/transmitter in cranial parasympathetic control of avian salt-gland secretion by acting on both the arteriolar network and the secretory tubules of the gland.     

Preferential localization of calcium-activated neutral protease in epithelial tissues

Immunohistochemical localization of calcium-activated neutral protease (CANP) in rabbit organs was determined using a monoclonal antibody against CANP. In most organs, epithelial tissues reacted intensely: these tissues include great alveolar and squamous alveolar cells in lung; interlobular artery, vein, and bile duct in liver; small vessels in skeletal muscle; glomeruli, juxtanglomerular cells, distal and collecting tubules in kidney; mucous epithelium in gallbladder; interstitial cells in testis; and cuboidal epithelial cells in brain choroid plexus. On the other hand, hepatocytes, epithelial cells which have ill defined basal lamina, were stained very faintly. These observations suggest that the physiological function of CANP is involved with transport systems in epithelial tissues through basal lamina.     

Changes in the protein spectrum of the chick embryo mesonephros and metanephros in the course of development

The protein spectra of two fractions (the soluble and the membrane fraction) of chick embryo kidney homogenates were isolated by electrophoresis on polyacrylamide gels with the aim of detecting the kidney differentiation process at the molecular level and, at the same time, of evaluating similarities in the construction of the mesonephros and metanephros at this level. Corresponding stages of the above two types of kidney were chosen for studying changes in protein structure during differentiation--i.e. the outset of differentiation (the 6-day mesonephros, the 11-day metanephros) and the stage of full maturity (the 14-day mesonephros, the 20-day metanephros). A total of 36 proteins was distinguished. The analysis of the protein spectra showed that the number of proteins changes but slightly during differentiation; the protein composition of the two types of kidney during differentiation altered by 20-35% of the total number of proteins; the similarity of the protein composition of the corresponding stages of mesonephros and metanephros, expressed as the proportion of the number of identical proteins, was greater than the mutual similarity of different developmental stages of the same type of kidney. The percentage of different proteins at corresponding stages of the kidneys varied from 5% to 23% of the total number of proteins detected.     

Effect of hydrocortisone and nicotinamide on gamma glutamyltransferase in primary cultures of rat hepatocytes

Summary Isolated rat hepatocytes cultured on collagen coated plates exhibit a gradual fetal phenotypic change during time in culture. The fetal liver marker gamma glutamyltransferase (GGT) was used to follow this change. Inasmuch as a significant overgrowth of nonparenchymal liver derived cells is seen frequently in primary cultures of hepatocytes, a technique was utilized that corrects for the presence of nonparenchymal cells. In media supplemented with either hydrocortisone (10⁻⁵ M) or nicotinamide (25 mM) the original epithelial morphology of hepatocytes was preserved for a longer period of time than in unsupplemented media. Hepatocytes in unsupplemented media exhibited an increase in GGT specific activity over time. Hydrocortisone (10⁻⁵ M) induced an increase in GGT activity compared to controls. Nicotinamide (25 mM) inhibited the increase in GGT activity compared to the unsupplemented hepatocytes. Our results indicate that GGT is regulated by hydrocortisone and nicotinamide. This study was supported by NIH Grant CA30241-01.