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Biomedical subjects

A Ribet

Publications and source records attributed to A Ribet.

At least 37 records · Page 2Linked to original sources
PubMed1988

Exocrine pancreatic secretion in the elderly.

In order to evaluate impairment of exocrine pancreatic function during aging, 27 subjects (mean age: 36 years +/- 7.8) and 28 subjects (mean age: 72 years +/- 3.2), with no clinical or radiological evidence of digestive disease, were selected. Duodenal aspirates over a 60 min period were obtained during continuous IV infusion of secretin (0.5 U/kg/h) and caerulein (75 ng/kg/h). Bicarbonate, lipase, chymotrypsin amylase concentrations and output were measured. Bicarbonate, lipase, chymotrypsin concentrations in the aged group were significantly reduced by 17%, 15% and 23% respectively (P less than 0.05) as compared with those in the young group. In addition, a significant reduction of approximately 45% in bicarbonate and enzyme output levels was observed. This study provides strong evidence for a marked functional involution of the exocrine pancreatic secretion during aging. The potential consequences of this phenomenon on the nutritional status in the elderly are discussed.

Adult↗
PubMed1988

The Ebner glands: a pancreatic-like gland secreting an acid lipase. Secretory regulation in vitro.

The lingual serous glands of rat tongue, the Ebner glands, secrete a potent acid lipase that acts in the stomach where it initiates the digestion of dietary fat. The factors affecting its secretion were studied 'in vitro' on Ebner slices. The lipolytic activity was measured in the incubation medium using tributyrine as substrate and by titration at pH: 5.4. Cholecystokinin (10(-9) M) and carbachol (10(-5) M) efficiently stimulated lipase secretion (3 fold over basal rate). The parasympathetic agent triggered secretion involving a calcium dependent system. Atropin (10(-4) M) blocked this cholinergic effect by about 40%. Lipase secretion was stimulated by epinephrine and isoproterenol. Propranolol (beta-antagonist) inhibited the adrenergic stimulation, while phentolamine was ineffective. The inhibitory effect of the selective beta 1-antagonist (Betaxolol) and the lack of effect of the selective beta 2-antagonist (ICI 118551) suggest the participation of beta 1-adrenoceptors in the secretion mechanism.

Adrenergic alpha-Antagonists↗
PubMed1988

Silent human pancreatic glucagonoma and "A" nesidioblastosis.

Surgical fragments of healthy and tumor-bearing pancreas from a patient with pancreatic tumor were studied by electron or light microscopy, histochemistry, and immunocytochemistry (human insulin, glucagon, somatostatin, gastrin, and bovine pancreatic polypeptide). Histological results were compared to those obtained by radioimmunoassay, both in tumor and serum. The tumor was identified as a glucagonoma because reactions for Grimelius' silver impregnation and immunoreaction with an antiserum against glucagon were positive and because a very high level of glucagon in the tumor was observed. Insulin, somatostatin, and gastrin levels remained normal, both in tumor and serum, but the glucagon level was normal in serum. Associated with this silent glucagonoma, an uncommon nesidioblastosis was also diagnosed with many A cells irregularly mixed with acinar cells, isolated or clustered in small groups. Acinar "intermediate" cells of "A" type were also observed. Such associative histopathological processes evoked possible development of an endocrine tumor from nesidioblastic-like tissue. Its embryogenic origin remained uncertain.

Adenoma, Islet Cell↗
PubMed1988

Distinct activation of Na+-H+ exchange by gastrin and CCK peptide in acini from guinea pig.

The effect of cholecystokinin (CCK)-gastrin family peptides (caerulein, unsulfated gastrin-17, and pentagastrin) and secretin in activating amiloride-sensitive 22Na uptake were investigated in guinea pig pancreatic acini. Secretin had no effect, but CCK-gastrin peptides stimulated the amiloride-sensitive 22Na uptake. The effect of caerulein was inhibited by dibutyryl guanosine 3',5'-cyclic monophosphate (cGMP) and asperlicin, indicating that activation of the Na+-H+ antiport caused by caerulein is mediated by CCK receptors. The effect of gastrin was dibutyryl cGMP and asperlicin insensitive, whereas the effect of pentagastrin was inhibited by the CCK antagonists but with a low affinity, indicating that the effect of gastrin and that of pentagastrin was CCK receptor independent. The calcium ionophore A23187 caused an increase in amiloride-sensitive 22Na uptake. However, the effect of caerulein, which increased internal calcium concentration, was not modified after depletion of intracellular calcium, and that of CCK-gastrin family peptides was not dependent on external calcium concentration. Activation of amiloride-sensitive 22Na uptake was also induced by 12-O-tetradecanoylphorbol 13-acetate and 1-oleoyl-2-acetyl-glycerol. Activation of protein kinase c may be involved in the mechanism of caerulein or gastrin in activating the Na+-H+ exchange.

Amiloride↗
PubMed1988

Functional somatostatin receptors on a rat pancreatic acinar cell line.

Somatostatin receptors from a rat pancreatic acinar cell line, AR4-2J, were characterized biochemically, structurally, and functionally. Binding of 125I-[Tyr11]somatostatin to AR4-2J cells was saturable, exhibiting a single class of high-affinity binding sites (Kd = 0.55 +/- 0.06 nM) with a maximal binding capacity of 258 +/- 20 fmol/10(6) cells. Somatostatin receptor structure was analyzed by covalently cross-linking 125I-[Tyr11]somatostatin to its plasma membrane receptors. Gel electrophoresis and autoradiography of cross-linked proteins revealed a peptide (Mr 80,000) containing the somatostatin receptor. Somatostatin inhibited vasoactive intestinal peptide (VIP)-stimulated adenosine 3',5'-cyclic monophosphate (cAMP) formation in a dose-dependent manner. The concentration of somatostatin that caused half-maximal inhibition of cAMP formation (IC50 = 0.4 nM) was close to the receptor affinity for somatostatin. Pertussis toxin pretreatment of AR4-2J cells prevented somatostatin inhibition of VIP-stimulated cAMP formation as well as somatostatin binding. We conclude that AR4-2J cells exhibit functional somatostatin receptors that retain both specificity and affinity of the pancreatic acinar cell somatostatin receptors and act via the pertussis toxin-sensitive guanine nucleotide-binding protein Ni to inhibit adenylate cyclase.

Adenylyl Cyclases↗
PubMed1988

[Comparison of fungal lipase and pancreatic lipase in exocrine pancreatic insufficiency in man. Study of their in vitro properties and intraduodenal bioavailability].

Assuming that acidic degradation of lipase was the major cause of failure for the correction of steatorrhea by pancreatic extracts, we compared the in vitro and in vivo activities of a fungal lipase (FL) (Rhizopus arrhizus) with classical porcine pancreatic extract (Eurobiol). The choice of FL was determined by its two optimum pH (3.5 and 7.4). Five factors known to modify lipase activity were tested: pH, biliary acids colipase, trypsin and albumin. Bioavailability was measured by using a double intubation method in 13 patients with severe pancreatic insufficiency. Each enzymatic preparation was given during a test meal in a randomized and cross-over fashion. Results of the in vitro study showed that FL differed from pancreatic lipase by the following properties: better resistance in acidic solution, inhibition by biliary salts, absence of effect of colipase and rapid degradation by trypsin. In vivo the percentage of lipase activity recovered was 14.2 +/- 10.6 p. 100 for FL and 56 +/- 50 p. 100 for the classical pancreatic preparation. Compared with placebo significant differences in the recovery rate of lipolytic activity were observed with the pancreatic preparation only and started at the 40th min after the end of the test meal. These results showed that lack of degradation in acidic milieu is not the only valuable criterion for the choice of an efficient lipase preparation. The role of other potential factors such as gastric emptying as well as proteolytic degradation of the enzyme should be considered as well.

Bile Acids and Salts↗
PubMed1987

Dexamethasone effects on somatostatin receptors in pancreatic acinar AR4-2J cells.

The effects of glucocorticoids on somatostatin binding and cAMP response in the rat pancreatic acinar carcinoma AR4-2J cell line were examined. Dexamethasone treatment reduced the number of somatostatin receptors 2.5 fold without any change in receptor affinity. In addition, dexamethasone increased the sensitivity of the cells to somatostatin-inhibited cAMP formation and restored the biphasic pattern of cAMP response to somatostatin previously observed in normal pancreatic acinar cells. Such effect may be associated with the glucocorticoid-promoted cellular pancreatic differentiation of AR4-2J cells.

Cyclic AMP↗
PubMed1987

Receptors for cholecystokinin and gastrin peptides display specific binding properties and are structurally different in guinea-pig and dog pancreas.

In the light of the strong potency of gastrin-related peptides on pancreatic exocrine secretion in dog, we analyzed the binding properties of peptides related to cholecystokinin (CCK) and gastrin on dog pancreatic acini compared to guinea-pig acini. Moreover, we determined apparent molecular masses of photoaffinity labelled CCK/gastrin receptors in the two models. Using the CCK radioligand, receptor selectivity towards CCK/gastrin agonists and antagonists was found to be lower in dog acini than in guinea-pig acini. Performing the binding with CCK and gastrin radioligands in combination with N2,O2'-dibutyryl-guanosine 3',5'-monophosphate, revealed that in dog acini there exist two different sub-classes of CCK/gastrin receptors having high and low selectivity, the latter ones being able to bind gastrin with high affinity (Kd = 2.1 nM). SDS-PAGE analysis of covalently cross-linked receptors using several photosensitive CCK and gastrin probes of different peptide chain lengths demonstrated that in guinea-pig, CCK peptides bound to a 84-kDa component whereas in dog pancreas, CCK and gastrin peptides bound to three distinct molecular species (Mr approximately equal to 78,000, 45,000, 28,000). Performing cross-linking in the presence of 1 microM CCK indicated that a 45-kDa protein is the putative CCK/gastrin receptor in dog pancreas. Our results support the concept of heterogeneity of CCK/gastrin receptors.

Affinity Labels↗
PubMed1987

Solubilization and characterization of guinea-pig pancreatic somatostatin receptors.

The solubilization of somatostatin receptors from guinea-pig pancreas by different non-denaturing detergents was investigated after stabilization of the receptors by prior binding of 125I-[Tyr11]somatostatin or its analogue 125I-[Leu8,DTrp22,Tyr25]somatostatin 28, to pancreatic plasma membranes. The somatostatin-receptor complexes were solubilized in a high yield by Zwittergent 3-14 (3-[tetradecyldimethylammonio]-1-propanesulfonate), a zwitterionic detergent. Other detergents, digitonin, Triton X-100, Chaps (3-[cholamidopropyldimethylammonio]-1-propanesulfonate) and octyl beta-D-glycopyranoside, achieved only partial solubilization. The recovery of receptor complexes was increased by glycerol. In order to characterize solubilized somatostatin-receptor complexes, membranes receptors were covalently labelled using N-5-azido-2-nitrobenzoyloxysuccinimide as cross-linking reagent before solubilization. Gel filtration chromatography analysis resulted in the identification of a major protein component of apparent Mr = 93,000 which interacted with the two radioligands. In addition, a similar component of Mr = 88,000 was characterized after analysis by SDS-PAGE of membrane receptors covalently cross-linked with 125I-[Leu8,DTrp22,Tyr25]somatostatin 28 by different heterobifunctional reagents: N-5-azido-2-nitrobenzoyloxysuccinimide, N-hydroxysuccinimidyl 4-azidobenzoate, N-succinimidyl 6-(4'-azido-2'-nitrophenylamino)hexanoate. Optimal cross-linking results were obtained with N-5-azido-2-nitrobenzoyloxysuccinimide. The solubilized somatostatin-receptor complex was adsorbed to wheat-germ agglutinin-agarose column and eluted by specific sugars. We concluded that the guinea-pig pancreatic somatostatin receptor in the membrane and in the non-denaturing detergent solution behaves as a protein monomer of apparent Mr approximately 85,000-90,000. The somatostatin receptor is a glycoprotein which contains complex-type carbohydrate chains.

Affinity Labels↗
PubMed1987

Characterisation of gastrin receptors on a rat pancreatic acinar cell line (AR42J). A possible model for studying gastrin mediated cell growth and proliferation.

Trophic changes of the exocrine pancreas after in vivo gastrin (G)/CCK treatment are well documented but up to now the study of the mechanisms involved is restricted by the lack of a suitable in vitro model. Nevertheless the in vivo trophic effect induced by gastrin/CCK peptides has been associated with an increase of ornithine decarboxylase (ODC) activity. In the present work, using the AR42J cell line in which CCK receptors and stimulation of amylase release by CCK peptides has already been demonstrated, we investigated the presence of gastrin binding sites and the possible modulation of proliferation by an inhibitor of ODC activity. 125I-BH-G17ns binding is saturable, reversible and specific. Potencies of the different analogues tested are G17ns greater than CCK8 greater than CCK8ns greater than or equal to G6s greater than G/CCK4. Furthermore dBt cGMP, a non-peptide antagonist for CCK receptors, does not compete for gastrin binding. This indicates the existence of a subclass of gastrin binding sites. Difluoromethyl ornithine (DFMO) (1 mM), an irreversible inhibitor of ODC, inhibits cell growth from day 3 up to day 7. This growth inhibition is dose dependent and closely related to an intracellular polyamine modulation. Putrescine and spermidine levels fell under detectable values while spermine levels increased. All these data suggest that this cell line could be a useful in vitro model to study the mechanisms of gastrin induced growth control.

Animals↗
PubMed1987

Processing of receptor-bound somatostatin: internalization and degradation by pancreatic acini.

We have previously demonstrated the presence of specific binding sites for somatostatin on plasma membranes from pancreatic acinar cells. In the present study we attempted to characterize the fate of receptor-bound 125I-[Tyr11]somatostatin. Internalization of somatostatin was rapid (reaching a plateau at 20% of the cell-associated specific radioactivity) and temperature dependent. To follow the processing of bound somatostatin, acini were incubated with 125I-[Tyr11]somatostatin at 5 degrees C during 16 h then, after washing, incubated at 37 degrees C for 90 min in fresh medium. Surface-bound somatostatin decreased rapidly, whereas radioactivity increased in the cell interior and the incubation medium. Intracellular and membrane-bound radioactivity was mainly intact 125I-[Tyr11]somatostatin. Degradation occurred at the plasma membrane level and led to iodotyrosine production. After 15 min of incubation, 15% of the initially surface-bound 125I-[Tyr11]somatostatin was compartmentalized within the cell, mainly in the microsomal fraction. After 30 min, a significant increase in radioactivity appeared in the nuclear fraction. These results indicate that the major part of somatostatin cellular degradation takes place at the plasma membrane level. Within the cell, somatostatin is routed to the nucleus via particular fractions sedimenting with microsomal vesicles.

Animals↗
PubMed1986

Dopamine receptors in pancreatic acinar cells from dog.

Dispersed acini from dog pancreas were used to characterize dopamine receptors in a study on the stimulation of cellular cyclic AMP formation and the binding of [3H]dopamine. Dopamine elicited concentration-dependent stimulation of cellular cyclic AMP with a maximal increase occurring at a concentration of 0.1 mM (EC50 = 1 microM). Epinine produced a potent stimulation similar to that by dopamine; the alpha-adrenoceptor agonists (amidephrine and noradrenaline) were less potent. Isoproterenol and apomorphine were ineffective. The effect of dopamine was potently blocked by dopamine receptor antagonists such as cis-(Z)-flupenthixol, haloperidol, fluphenazine, whereas spiperone, sulpiride and domperidone were weakly active. Apomorphine acted as an antagonist to inhibit dopamine-stimulated cellular cyclic AMP formation as well as phenoxybenzamine. Yohimbine, prazosin or clonidine were poorly or not active. The affinity of agents to stimulate cellular cyclic AMP formation or to inhibit dopamine-stimulated cellular cyclic AMP formation was closely related to their affinity to inhibit the binding of [3H]dopamine to pancreatic acini, providing evidence that dopamine binding sites are receptors that mediate the action of dopamine on cAMP accumulation. This was further substantiated by the demonstration of specific binding sites for [3H]cis-(Z)-flupenthixol.

Adrenergic alpha-Antagonists↗
PubMed1986

Molecular properties of solubilized CCK receptor from guinea-pig pancreas.

In order to characterize the CCK receptor in guinea-pig pancreas, iodinated CCK-39 was bound to pancreatic membranes and the reversible complex was solubilized using various non-denaturing detergents. In term of recovery of ligand stabilized receptors, the relative potencies were Zwittergent 3-14 greater than CHAPS = CHAPSO greater than digitonin greater than MEGA 10 greater than octyl beta-D-glucopyranoside. The stability of receptor complexes was increased by glycerol. Chromatographic analysis revealed that digitonin was the most efficient detergent for disaggregation of CCK receptor complex since it yielded a 76 kDa component in addition to the large components obtained after solubilization with CHAPS and Zwittergent. Furthermore, CCK receptors were covalently labelled using dissuccinimidyl suberate or UV irradiation of labelled membranes by photoactivable radioiodinated CCK-39 and subsequently solubilized by CHAPS + SDS or by SDS alone. A predominant molecule was characterized by chromatography (76 kDa) and SDS-PAGE (89 kDa). In addition to this component, other components having molecular masses of 130-150 kDa, 57 kDa and 40 kDa were detected by SDS-PAGE. They correspond to minor bands. These bands, except the 40 kDa band, were protected from covalent labelling by the presence of CCK-39 (10(-6) M) during initial incubation. Reduction under beta-mercaptoethanol mainly resulted in the decrease of high molecular weight aggregates (Mr greater than 200 kDa). We concluded that for a given detergent a specific molecular weight pattern of solubilized CCK receptor complex is achieved. The minimal component had a molecular mass of 71-84 kDa according to the method of biochemical analysis used.

Animals↗
PubMed1986

Interaction of [125I]-Tyr4-bombesin with specific receptors on normal human pancreatic membranes.

The binding of bombesin to its receptors on normal human pancreatic membranes was investigated using high specific activity, radioiodinated bombesin ([125I]-Tyr4-bombesin), prepared by an oxidative method with chloramine-T. Binding was specific, temperature-dependent, saturable, reversible and linearly related to membranes protein concentration. After a 30 min period of incubation with membranes the degradation of the tracer has never been found superior to 20%. Scatchard analysis of binding data was compatible with a single class of binding sites with a high affinity (0.96 nM) and a Bmax of 753 fmol/mg protein. [125I]-Tyr4-bombesin binding to human pancreatic membranes was competitively inhibited by (1-Tyr4-)bombesin, GRP, the nonapeptide of bombesin and litorin but not by unrelated hormones such as somatostatin, CCK, human gastrin, etc. These results describe for the first time the presence of specific receptors for bombesin on human pancreatic membranes. The binding characteristics obtained are comparable with those found in other species.

Bombesin↗
PubMed1986

Analysis of somatostatin peptides produced by an endocrine pancreatic cell line.

Biological active forms of somatostatin are produced by cleavage of large precursors. If the sequence of the pre-proform of somatostatin has been deduced from cDNA structure in several species, little is known about the processing of these large precursors. For this purpose, the analysis of immunoreactive components secreted by the R.I.N. cell line was investigated. After selection of a cell population and culture conditions providing the optimal production of these peptides, analysis of their molecular forms was done by molecular gel filtration. The results show that mainly pro-forms accumulate in the culture medium while besides the pre-proform the smaller immunoreactive species behaving like S-28 and S-14 were found in cell extracts. Incorporation studies in serum free medium showed rapid formation of an intermediate compound eluted at 1.87 V0.

Animals↗
PubMed1986

VIP regulation of a human pancreatic cancer cell line: Capan-1.

VIP and secretin control the secretory function of the normal pancreas. We analysed their regulatory functions in a human pancreatic cancer cell line: Capan-1. Saturation binding experiments with 125I-VIP showed the existence of one class of binding sites of very high affinity: KD 6.4 +/- 3.0 X 10(-11) M and a low Bmax: 12 fmoles/10(6) cells, in both intact cells and membrane preparations. This site has not yet been described in normal or tumorous digestive cells. Competition binding experiments let us characterize two more binding sites, KD: 2.1 +/- 0.7 X 10(-9) M and 5.0 +/- 0.6 X 10(-8) M and the corresponding Bmax: 120 and 500 fmoles/10(6) cells. These sites are similar to those found on cells of the digestive tract. Competition binding experiments gave the following IC50: 3.0 +/- 0.9 X 10(-9) M for VIP; 2 +/- 0.6 X 10(-6) M for PHI; and 1 +/- 0.7 X 10(-5) M for secretin. VIP elicited a cAMP rise, the half maximal response being obtained at 1.2 X 10(-10) M. Secretin induced a cAMP response but only for concentrations higher than 10(-8) M. VIP receptors were found to be modulated by two factors: cell ageing and cell density. Cells chronically treated with VIP showed a slight decrease of their proliferation; insulin exerted an opposite effect. It is concluded that at the difference of normal pancreatic cells, the present cell line lacks secretin-preferring receptors and acquires some of the properties of intestinal cells.

Binding, Competitive↗