In vitro testing of artificial heart valves: comparison between Newtonian and non-Newtonian fluids

The in vitro testing of artificial heart valves is often performed with simple fluids like glycerol solutions. Blood, however, is a non-Newtonian fluid with a complex viscoelastic behavior, and different flow fields in comparable geometries may result. Therefore, we used different polymer solutions (Polyacrylamid, Xanthan gum) with blood-like rheological properties as well as various Newtonian fluids (water, glycerol solutions) in our heart valve test device. Hydrodynamic parameters of Björk-Shiley heart valves with a tissue annulus diameter (TAD) of 21-29 mm were investigated under aortic flow conditions. Major results can be summarized as follows. The mean systolic pressure differences depend on the model fluids tested. Closing time and closing volume are not influenced by the rheological behavior of fluids. These parameters depend on TAD and the pressure differences across the valve. In contrast, rheological behavior has a pronounced influence upon leakage flow and leakage volume, respectively. Results show furthermore that the apparent viscosity data as a function of shear rate are not sufficient to characterize the rheological fluid behavior relevant to hydrodynamic parameters of the heart valves investigated. Therefore, similarity in the yield curves of non-Newtonian test fluids mimicing blood is only a pre-requisite for a suitable test fluid. More information about the viscous and elastic component of the fluid viscosity is required, especially in geometries where a complex flow field exists as in the case of leakage flow.

Regulation of corticosteroid-binding globulin synthesis by 1alpha,25-dihyroxy-vitamin D3 (calcitriol), 9-cis-retinoic acid and triiodothyronine in cultured rat fetal hepatocytes

Evidence regarding the nature of the regulatory factors which directly act upon liver cells and extra-hepatic tissues to alter CBG synthesis is scarce. The present study used cultured rat fetal hepatocytes to investigate the involvement and possible interplay in this process of several members of the nuclear receptors superfamily: vitamin D (VDR), retinoic acids (RAR/RXR) and thyroid hormones (TR). Treatment of cells with 1alpha,25-(OH)2D3 (1,25-D) elicited a dose-dependent inhibition of basal CBG concentration in culture medium. Maximum inhibition to about 15% of control level was achieved with 0.1-1.0 nM, with an IC50 of 3.8 x 10(-12) M and with no significant change in binding affinity. Differential activation of RAR and RXR with either 9-cis-retinoic acid (9-cis-RA) or the RAR-selective synthetic retinoid TTNPB revealed that high doses of both drugs diminished CBG expression, though the former proved about 10-times more potent than the latter in this regard. Amplification by triiodothyronine (T3) of CBG synthesis failed to block the inhibitory effects of either 1,25-D or retinoids, as revealed by both binding capacity and mRNA measurements. Relative to CBG, 1,25-D similarly depressed the synthesis of alpha-fetoprotein (AFP), while on the contrary, retinoids and T3 were shown to cause opposite effects, as 9-cis-RA and TTNPB elevated and T3 decreased AFP expression. The present findings identify for the first time ligands of VDR and RAR/RXR as powerful negative regulators of both basal and T3-stimulated CBG biosynthesis in fetal hepatocytes and suggest lack of a functional interplay between TR and VR or RAR/RXR in these processes.

[Prevalence of human herpesvirus 7 in Mexican blood donors]

The human herpes virus 7 (HHV-7) has been recently isolated from CD4 cells of healthy persons. The present study describes the antibody prevalence of this virus in a healthy Mexican population. Two hundred blood samples from candidates for blood donation at the Hospital General de Mexico were studied with the indirect immunofluorescence test (IFA) in HHV-7 infected SupT1 cells. The testing was done in the University of Cologne, Germany; 167 were males and 33 female; the donors came from 12 of the 31 states in the Mexican republican, predominantly from Mexico City (60.5%) and the State of Mexico (28%). Their mean age was 29.2 years. All but three samples were positive to the HHV-7 (98.5% positivity). Nearly 85% had high titers (> or = 1:80). Other serology testing in the samples revealed 1% positive tests to hepatitis B, 2% to syphilis, and 0.5% to brucella. Hepatitis C and the HIV test were negative in all. The high prevalence of HHV-7 in our donor population should be further studied in order to determine titers indicative of an active infection and of their association with illnesses.

The B lymphocyte in rheumatoid arthritis: analysis of rearranged V kappa genes from B cells infiltrating the synovial membrane

The participation of the humoral immune system in rheumatoid arthritis (RA) is characterized by the production of rheumatoid factors (RF). RF are autoantibodies against the Fc part of IgG which are encoded by diverse germ-line genes. Most of the RF-encoding genes are unmutated, but in RA, a substantial quantity is encoded by somatically mutated genes. In addition, the synovial membranes (SM) of the diseased joints of RA patients are infiltrated by B lymphocytes which form germinal center-like aggregates. To analyze the local immune response, B cell foci from two RA SM were isolated by micromanipulation. From DNA of these foci, the rearranged kappa light chain variable region (V kappa) genes were amplified by polymerase chain reaction (PCR), cloned and sequenced. The amplification of different V kappa-J kappa combinations of different foci suggested oligoclonal expansion of B lymphocytes, which was confirmed by sequence analysis: each PCR product contained members of a single B cell clone. The sequence analysis of 29 different clones revealed rearrangements of diverse V kappa genes. Both frequent representatives of the V kappa 3 and the V kappa 1 family, as well as rarely used genes such as the L10 and B2 genes of the V kappa 2 and V kappa 5 families were found. Of the eleven potentially functional gene rearrangements, eight were significantly mutated, indicating their derivation from antigen-selected B cells. Intraclonal diversity in one of these clones may suggest ongoing mutation in the diseased synovial membrane of patients with RA.

Characterisation of the neurosensory elements of the feline cranial cruciate ligament

The identification and distribution of mechanoreceptors in the cranial cruciate ligament of the cat (analogous to the anterior cruciate ligament in other species) was studied histologically using a modified celloidin embedding technique to achieve serial sectioning of bone-ligament-bone preparations with gold chloride staining. We identified distinctive large elongated structures situated between the collagen bundles of the ligament (resembling endings described as Freeman and Wyke type III; also termed Golgi tendon receptors). These endings were found near the middle of the ligament well away from the bone-ligament junction. Axons seen entering only one end of each type III ending helped to confirm its neural basis. While we saw structures resembling types I and II endings (i.e. Ruffini and pacinian endings, respectively) in individual sections, serial sections failed to reveal convincing evidence of their existence. Such structures almost always appeared to be vascular in nature on adjacent sections, with vessels entering and exiting. We conclude that serial sections are critical to interpreting the presence or absence of mechanoreceptors.

Purification and characterization of recombinant cytochrome P450TYR expressed at high levels in Escherichia coli

The multifunctional tyrosine N-hydroxylase, cytochrome P450TYR (CYP79), from Sorghum bicolor catalyzing the conversion of tyrosine to p-hydroxyphenyl-acetaldoxime in the biosynthesis of the cyanogenic glucoside dhurrin, has been expressed in Escherichia coli using the isopropyl-beta-D-thiogalactopyranoside-inducible vector pSP19g10L, containing the cDNA encoding CYP79. The expression construct was optimized by reducing the length of the N-terminal hydrophobic core of the signal sequence of cytochrome P450TYR and by exchanging the first eight codons with the first eight codons of bovine P45017 alpha. The highest yielding construct provided 200-500 nmol P450TYR/liter cell culture. The recombinant P450TYR was gently and efficiently extracted from E. coli spheroblasts by temperature-induced phase partitioning of Triton X-114 in the presence of 30% glycerol and isolated by DEAE and reactive red chromatography. In reconstitution experiments using saturating amounts of sorghum NADPH-cytochrome P450 reductase, the Km and turnover rate for isolated recombinant P450TYR was 0.22 +/- 0.06 mM and 49.2 +/- 3.8 min-1, respectively, whereas a turnover rate as high as 350 min-1, was obtained using E. coli membranes. Addition of 3 mM glutathione stimulated the activity of reconstituted P450TYR and of sorghum microsomes although the effect was highly variable. Phenylalanine, the precursor of several cyanogenic glucosides, gave a type I binding spectrum, but was not metabolized by P450TYR, demonstrating the high substrate specificity of this P450. Administration of radioactively labeled p-hydroxyphenylacetaldoxime to E. coli cells, showed E. coli metabolized p-hydroxyphenylacetaldoxime independent of the expression of P450TYR.

Azure B-eosin APAAP staining: a method for simultaneous hematological and immunological cell analysis

Azure B-eosin APAAP staining allows simultaneous analysis of peripheral blood and bone marrow cells for hematological characteristics and immunological cell marker profiles. A defined sequence of staining procedures maintains characteristic components of the Romanowsky-Giemsa stain whereas cell antigens can be detected immunologically using the alkaline phosphatase-anti-alkaline phosphatase (APAAP) detection system. Antigens are visualized by the staining product of the substrate-naphthol AS GR phosphate and variamine blue salt. The usefulness of the azure B-eosin APAAP method was demonstrated on blood and bone marrow smears of patients with various hematological disorders.

Multifactorial regulation of pituitary adenylate cyclase-activating polypeptide (PACAP)-induced production of cyclic AMP in ATT-20 corticotrophs: major involvement of Rolipram-sensitive and insensitive phosphodiesterases

Cyclic nucleotide phosphodiesterases (PDEs) appear to play a major role in the modulation of cellular accumulations of cAMP/cGMP and hence the magnitude of the cell response to a hormone signal. These enzymes are present in cells as multiple isoforms and lie under control of various protein kinases. Because PACAP, unlike corticotropin-releasing factor (CRF), may stimulate a dual signalling pathway in pituitary cells (activating both adenylyl cyclase and phospholipase C), we used AtT-20 corticotrophs and primary cultures of rat pituitary cells to study the effect and possible differential influence of these peptides on cAMP formation. Time-course analysis indicated that, both in the absence and the presence of Rolipram (a selective type IV PDE inhibitor), PACAP stimulated a rapid and short-lived accumulation of cAMP in tumor corticotrophs, while in the presence of the non-selective inhibitor IBMX, the peptide produced a sustained high plateau level of second messenger (10 times the level generated with Rolipram at 20 min). On the contrary, when exposed to CRF, cAMP production augmented in parallel, irrespective of whether Rolipram or IBMX were present. The differential effects of the PDE inhibitors were seen with PACAP concentrations ranging from 0.1 to 100 nM, and could also be demonstrated in primary cultures of pituitary cells. Co-incubation of AtT-20 cells with Rolipram along with inhibitors of type I (but not of type III) PDEs, enhanced cAMP formation elicited by PACAP to a level significantly higher than that induced by CRF.(ABSTRACT TRUNCATED AT 250 WORDS)

[Initial studies of the prevalence of human Herpesvirus 7 (HHV-7) in Mexican blood donors]

Human herpesvirus 7 (HHV-7) has been recently isolated from CD4-positive peripheral blood lymphocytes of a healthy person. The present study was performed to find the antibody prevalence of this virus in the healthy Mexican population. Two hundred blood samples from candidates for blood donation at the General Hospital of Mexico were studied with the indirect immunofluorescence test (IFA) in HHV-7 infected SupT1 cells. 83.5% were male persons and 16.5% female, the mean age for the male group was 28.8 years and for the female group 31.5. The donors came from 12 different states in Mexico, predominantly from the city (60.8%), and had different occupations. Almost all samples (98.5%) were positive to HHV-7. Other studies done revealed 1% positive to brucella, 1% positive to Hepatitis B, 2% positive to syphilis, hepatitis C and HIV test were negative in the whole group studied. There was a high incidence of HHV-7 in the group studied: more than 50% of the subject had high titers. This results should be further studied determine titers indicative of an active infection and to search for any association with illnesses.

[Apoptosis and cell proliferation in HHV-6 infections. Regulatory mechanisms of p53/bcl-2/ras interactions]

HHV-6 infected immature T (HSB2) and Hodgkin (HDLM2) cells and biopsy tissues from lymph nodes of patients with Hodgkin's disease (HD) and Kikuchi lymphadenitis (KL) were studied immunohistologically for virus antigen expression and for the oncogene/anti-oncogene products ras, bcl-2 and p53. Cell proliferation and cell death were tentatively monitored in tissue culture by PCNA staining, by viability testing and in situ end labeling of fragmented DNA. PCNA was also used in biopsy samples. KL is characterized by high incidences of focal cell death (i.e. histiocytic necrotizing lymphadenitis), while HD is apparently more a proliferative disease. The techniques used revealed no significant differences in the cellular expression of viral DNA or antigens among cell lines, HD or KL. The HDLM2 cell line with the superior survival after HHV-6 infection showed a significantly lower expression of p53 and PCNA than HSB2 cells. Biopsy samples from patients with KL did not express p53, and ras and PCNA were observed in fewer cells than in HD. Bcl-2, however, was significantly more frequently seen than in HD. The interpretation of the data is difficult; they suggest that there are additional regulatory influences in control of cell proliferation and cell death, such as cytokines and growth factors, which are altered after viral infection. Also, virus-induced cell death probably includes other mechanisms besides apoptosis, such as cell damage caused by oxygen radicals.

Cytochrome P-450TYR is a multifunctional heme-thiolate enzyme catalyzing the conversion of L-tyrosine to p-hydroxyphenylacetaldehyde oxime in the biosynthesis of the cyanogenic glucoside dhurrin in Sorghum bicolor (L.) Moench

Cytochrome P-450TYR, which catalyzes the N-hydroxylation of L-tyrosine in the biosynthesis of the cyanogenic glucoside dhurrin in Sorghum bicolor (L.) Moench has recently been isolated (Sibbesen, O., Koch, B., Halkier, B. A., and Møller, B. L. (1994) Proc. Natl. Acad. Sci. U.S.A. 92, 9740-9744). Reconstitution of the enzyme activity in lipid micelles containing cytochrome P-450TYR and NADPH-cytochrome P-450 oxidoreductase demonstrates that cytochrome P-450TYR catalyzes the conversion of L-tyrosine into p-hydroxyphenylacetaldehyde oxime. Earlier studies with microsomes have demonstrated that this conversion involves two N-hydroxylation reactions of which the first produces N-hydroxytyrosine. We propose that the product of the second N-hydroxylation reaction is N,N-dihydroxytyrosine. N,N-dihydroxytyrosine is dehydrated to 2-nitroso-3-(p-hydroxyphenyl) propionic acid which decarboxylates to p-hydroxyphenylacetaldehyde oxime. The dehydration and decarboxylation reactions may proceed non-enzymatically. The E/Z ratio of the p-hydroxyphenylacetaldehyde oxime produced by reconstituted cytochrome P-450TYR is 69:31. Lipid micelles made from L-alpha-dilauroyl phosphatidylcholine are more than twice as effective in reconstituting cytochrome P-450TYR activity as compared to other lipids. The Km and turnover number of the enzyme is 0.14 mM and 200 min-1, respectively, when assayed in the presence of 15 mM NaCl whereas the values are 0.21 mM and 230 min-1 when assayed in the absence of added salt. The multifunctional nature cytochrome P-450TYR is confirmed by demonstrating that binding of L-tyrosine or N-hydroxytyrosine mutually excludes binding of the other substrate. These results explain why the conversion of tyrosine to p-hydroxyphenylacetaldehyde oxime as earlier reported (Møller, B. L., and Conn, E. E. (1980) J. Biol. Chem. 255, 3049-3056) shows the phenomenon of catalytic facilitation ("channeling"). Cytochrome P-450TYR is the first isolated multifunctional heme-thiolate enzyme from plants. N-Hydroxylases of the cytochrome P-450 type with high substrate specificity have not previously been reported.

Characterization of cytochrome P450TYR, a multifunctional haem-thiolate N-hydroxylase involved in the biosynthesis of the cyanogenic glucoside dhurrin

The haem-thiolate N-hydroxylase cytochrome P450TYR involved in the biosynthesis of the tyrosine-derived cyanogenic glucoside dhurrin in Sorghum bicolor had recently been isolated. Reconstitution of enzyme activity by insertion of cytochrome P450TYR and NADPH-cytochrome P450-reductase into L-alpha-dilauroylphosphatidylcholine micelles and using tyrosine as substrate results in the formation of p-hydroxyphenylacetaldehyde oxime. Quantitative substrate binding spectra demonstrate that tyrosine and N-hydroxytyrosine are mutually exclusive substrates that bind to the same active site of cytochrome P450TYR. The multifunctionality of cytochrome P450TYR has been confirmed in reconstitution experiments using recombinant cytochrome P450TYR expressed in Escherichia coli. It was earlier reported that an in vitro microsomal system catalyzing all but the last step in the biosynthetic pathway for cyanogenic glucosides exhibits catalytic facilitation (channelling). This observation is explained by the multifunctionality of cytochrome P450TYR. The cytochrome P450TYR sequence represents the first amino acid sequence of a functionally characterized cytochrome P-450 enzyme from a monocotyledonous plant and the first sequence of an N-hydroxylase with high substrate specificity. Multifunctional N-hydroxylases of the cytochrome P-450 type have not previously been reported in living organisms.

Pituitary adenyl cyclase-activating peptide: a hypophysiotropic factor that stimulates proopiomelanocortin gene transcription, and proopiomelanocortin-derived peptide secretion in corticotropic cells

The biological effects of pituitary adenylate cyclase-activating peptide (PACAP) 27 and 38 on peptide secretion and gene regulation were studied in the mouse corticotrope-derived cell line AtT20. Treatment of these cells with PACAP 27/38 led to a dose-dependent increase in cAMP content and ACTH accumulation in the medium with an apparent ED50 value close to 10(-9) M. The genomic effects of PACAP were first investigated by using a reporter gene containing a cAMP responsive element (CRE: TGACGTCA) PACAP 27/38 stimulate transcription from this construction and the effect is further increased when cells are cotreated with the phosphodiesterase inhibitor rolipram. Furthermore, we show by measuring nuclear heterologous proopiomelanocortin (POMC) RNA levels or by using a reporter gene containing the POMC promoter region, that PACAP stimulates POMC transcription. This transcriptional stimulation is mediated by the cAMP-dependent protein kinase (PKA) since genetic inactivation of PKA by a dominant inhibitory mutant of this enzyme completely abolished the effect of PACAP on POMC transcription. Finally, we show that the transcriptional stimulation of POMC by PACAP is repressed by the glucocorticoid receptor agonist dexamethasone. Taken together, these data suggest that PACAP is a hypophysiotropic hormone that exert similar if not identical functions as corticotropin-releasing hormone (CRH) on corticotrope cells.

Isolation of the heme-thiolate enzyme cytochrome P-450TYR, which catalyzes the committed step in the biosynthesis of the cyanogenic glucoside dhurrin in Sorghum bicolor (L.) Moench

The cytochrome P-450 enzyme (hemethiolate enzyme) that catalyzes the N-hydroxylation of L-tyrosine to N-hydroxytyrosine, the committed step in the biosynthesis of the cyanogenic glucoside dhurrin, has been isolated from microsomes prepared from etiolated seedlings of Sorghum bicolor (L.) Moench. The cytochrome P-450 enzyme was solubilized with the detergents Renex 690, reduced Triton X-100, and 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate and isolated by ion-exchange (DEAE-Sepharose) and dye (Cibacron blue and reactive red 120) column chromatography. To prevent irreversible aggregation of the cytochrome P-450 enzyme, the isolation procedure was designed without any concentration step--i.e., with dilution of the ion-exchange gel with gel filtration material. The isolated enzyme, which we designate the cytochrome P-450TYR enzyme, gives rise to the specific formation of a type I substrate binding spectrum in the presence of L-tyrosine. The microsomal preparation contains 0.2 nmol of total cytochrome P-450/mg of protein. The cytochrome P-450TYR enzyme is estimated to constitute approximately 20% of the total cytochrome P-450 content of the microsomal membranes and about 0.2% of their total protein content. The apparent molecular mass of the cytochrome P-450TYR enzyme is 57 kDa, and the N-terminal amino acid sequence is ATMEVEAAAATVLAAP. A polyclonal antibody raised against the isolated cytochrome P-450TYR enzyme is specific as monitored by Western blot analysis and inhibits the in vitro conversion of L-tyrosine to p-hydroxymandelonitrile catalyzed by the microsomal system. The cytochrome P-450TYR enzyme exhibits high substrate specificity and acts as an N-hydroxylase on a single endogenous substrate. The reported isolation procedure based on dye columns constitutes a gentle isolation method for cytochrome P-450 enzymes and is of general use as indicated by its ability to separate cytochrome P-450TYR from the cytochrome P-450 enzyme catalyzing the C-hydroxylation of p-hydroxyphenylacetonitrile and from cinnamic acid 4-hydroxylase.

[Testing the hydrodynamic properties of heart valve prostheses with a new test apparatus]

A new test apparatus for the testing of artificial heart valves makes it possible to realize both physiological flow through the valve during the flow period, and physiological pressure differences across the artificial valve during the closing phase, both for aortic and mitral valve positions, with freely selectable stroke volume and heart frequency. The major hydraulic parameters of the valve are measured directly (pressure drop, closing volume and closing time, leakage volume) or are calculated (e. g. energy loss). In association with the demonstration of the suitability of the HKP+ test apparatus for the measurement of hydraulic parameters in accordance with ISO 5840, the hydraulic properties of various types and sizes of valve with respect to pressure drop (resistance), together with their closing behaviour and leakage flow, are described for different fluids, and the correlations shown.

Isolation of autophagocytosis mutants of Saccharomyces cerevisiae

Protein degradation in the vacuole (lysosome) is an important event in cellular regulation. In yeast, as in mammalian cells, a major route of protein uptake for degradation into the vacuole (lysosome) has been found to be autophagocytosis. The discovery of this process in yeast enables the elucidation of its mechanisms via genetic and molecular biological investigations. Here we report the isolation of yeast mutants defective in autophagocytosis (aut mutants), using a rapid colony screening procedure.

Glucocorticoids, but not dopamine, negatively regulate the melanotrophic activity of the rabbit pituitary intermediate lobe

The leporidae (rabbit and hare) pituitary intermediate lobe (IL) differs from that of other mammals by its neuroendocrine regulation. In particular, it is not submitted to the classic dopaminergic inhibitory control, which has been considered as a repressive factor for the expression of glucocorticoid receptors (GR) in the mammalian IL. Hence, the present experiments aimed at examining the rabbit IL for the possible existence of GR. Using both immunocytochemistry and binding studies with (3H)-dexamethasone, we localized GR in the nuclei of IL cells and showed the presence of saturable and high-affinity type II receptor sites, with Kd approximately 3.9 nM. Also, exposure of cultured IL cells to 10 nM dexamethasone (DEX) resulted in the blockade of melanocyte-stimulating hormone (alpha MSH) secretion stimulated by oxytocin (OT). Importantly, the inhibitory effect was reversed by a 100-fold excess of the glucocorticoid antagonist RU 38486. This is the first study which clearly demonstrates in a mammalian IL, namely the rabbit, the presence of functional GR, involved in the negative regulation of the melanotrophic activity of this gland.

Inhibition of protein phosphatases by okadaic acid and calyculin-A differentially modulates hormonal- and forskolin-stimulated formation of cyclic AMP in AtT-20 corticotrophs: effect of pituitary adenylate activating polypeptide and corticotropin-releasing factor

The effect of phosphatase inhibitors okadaic acid and calyculin-A on cAMP formation and adrenocorticotropic hormone (ACTH) secretion in AtT-20 corticotrophs was investigated. Both okadaic acid and calyculin-A inhibited dose-dependently the accumulation of cAMP in cells stimulated with pituitary adenylate cyclase activating factor (PACAP) and corticotropin-relating hormone (CRF). While in the case of okadaic acid the half-maximum inhibiting concentration was similar for both peptides (IC50 = 4 x 10(-7) M), it appeared that calyculin-A was about one order of magnitude more efficient in inhibiting the effect of PACAP than that of CRF (IC50 = 3.8 x 10(-9) M vs 2.0 x 10(-8) M, respectively). Importantly, the inhibitors blocked the activation by cholera toxin (which acts on Gs-like proteins) of cAMP formation, but failed to alter the effect of forskolin (which bypasses the receptor-G protein complex and activates adenylyl cyclase directly). Treatment of cells with calyculin-A significantly dampened adenylyl cyclase activity in cell membrane fraction, though to a lesser extent than it blocked cAMP formation in the whole cell. Both okadaic acid and calyculin-A inhibited CRF- and PACAP-induced secretion of ACTH. Our data hint that in AtT-20 corticotrophs, inhibition of phosphatases by modulating the state of phosphorylation of the receptor-G proteins complexes for CRF and PACAP, regulates cAMP formation and ACTH secretion.

Precocious and reversible expression of sucrase-isomaltase unrelated to intestinal cell turnover

The effect of starvation and refeeding on the developmental pattern of intestinal sucrase-isomaltase (SI) was analyzed in preweaned rats. Starvation at postnatal day 12 caused a precocious expression of SI activity and mRNA. Alkaline phosphatase activity was slightly reduced, and no significant change was observed for aminopeptidase and lactase activities. Immunostaining showed that SI molecules appear in cells at the base of the villus. Sucrase expression was further increased by prolonged food deprivation, whereas enzyme activity as well as the amount of SI mRNA dropped to reach the low level found in control sucklings when 48 h-starved pups were refed by returning them to their dams. During the refeeding period, the enterocytes that were committed to produce SI by starvation continued to express the enzyme while migrating up the villi. However, the new epithelial cells arising from the crypts no longer synthesized the disaccharidase. The starvation-evoked appearance of SI was preceded by a transient burst of expression of the protooncogene c-fos, an event that may be correlated to the ontogenic rise of c-fos mRNA observed before weaning. However, in contrast to the normal weaning condition, SI induction by starvation occurred without obvious increase of epithelial cell proliferation and turnover. During the starvation and refeeding period, patterns of sucrase activity and SI mRNA paralleled the serum level of glucocorticoids.(ABSTRACT TRUNCATED AT 250 WORDS)