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Biomedical subjects

Y Okabayashi

Publications and source records attributed to Y Okabayashi.

At least 19 recordsLinked to original sources
PubMed1998

Liposome immunoassay by long-lived fluorescence detection.

Immunoassay by fluorescence energy transfer from a europium chelate in liposome to allophycocyanin (APC) was demonstrated. Streptavidin or antibody to biotin was bonded to the liposome containing the europium chelate of 2-naphthoyltrifluoroacetone in the bilayer. When the biotin bonded to APC (APC-BT) was added to the prepared liposomes and the long-lived fluorescence (lambda ex 336 nm, lambda em 665 nm, delay time 0.05 ms, gate time 3.9 ms) was measured by a flow system, the fluorescence energy of the europium chelate was found to be transferred to APC-BT and the long-lived fluorescence intensity to increase linearly as the concentration of APC-BT (1-10 micrograms ml-1) increased. Further, the intensity decreased competitively with the concentration of biotin (0.1-100 microM) when biotin was added to the liposome solution containing a constant concentration of APC-BT.

Animals↗
PubMed1998

Shc phosphotyrosine-binding domain dominantly interacts with epidermal growth factor receptors and mediates Ras activation in intact cells.

The adaptor protein Shc contains a phosphotyrosine binding (PTB) domain and a Src homology 2 (SH2) domain, both of which are known to interact with phosphorylated tyrosines. We have shown previously that tyrosine 1148 of the activated epidermal growth factor (EGF) receptor is a major binding site for Shc while tyrosine 1173 is a secondary binding site in intact cells. In the present study, we investigated the interaction between the PTB and SH2 domains of Shc and the activated human EGF receptor. Mutant 52-kDa Shc with an arginine-to-lysine substitution at residue 175 in the PTB domain (Shc R175K) or 397 in the SH2 domain (Shc R397K) was coexpressed in Chinese hamster ovary cells overexpressing the wild-type or mutant EGF receptors that retained only one of the autophosphorylation sites at tyrosine 1148 (QM1148) or 1173 (QM1173). Shc R397K was coprecipitated with the QM1148 and QM1173 receptors, was tyrosine-phosphorylated, and associated with Grb2 and Sos. In contrast, coprecipitation of Shc R175K with the mutant receptors was barely detectable. In cells expressing the QM1173 receptor, Shc R175K was tyrosine-phosphorylated and associated with Grb2, while association of Sos was barely detectable. In cells expressing the QM1148 receptor, tyrosine phosphorylation of Shc R175K was markedly reduced. When both Shc R175K and 46-kDa Shc R397K were coexpressed with the mutant receptors, p46 Shc R397K was dominantly tyrosine-phosphorylated. In cells expressing the wild-type receptor, Shc R397K, but not Shc R175K, translocated to the membrane in an EGF-dependent manner. In addition, Ras activity stimulated by the immunoprecipitates of Shc R397K was significantly higher than that by the immunoprecipitates of Shc R175K. The present results indicate that tyrosine 1148 of the activated EGF receptor mainly interacts with the Shc PTB domain in intact cells. Tyrosine 1173 interacts with both the PTB and SH2 domains, although the interaction with the PTB domain is dominant. In addition, Shc bound to the activated EGF receptor via the PTB domain dominantly interacts with Grb2-Sos complex and plays a major role in the Ras-signaling pathway.

Adaptor Proteins, Signal Transducing↗
PubMed1997

Epidermal growth factor stimulates the tyrosine phosphorylation of SHPS-1 and association of SHPS-1 with SHP-2, a SH2 domain-containing protein tyrosine phosphatase.

SHPS-1 is a 120 kDa glycosylated receptor-like protein that contains immunoglobulin-like domains in its extracellular region and four potential tyrosine phosphorylation for SH2 domain binding sites in its cytoplasmic region. Epidermal growth factor (EGF) stimulated the rapid tyrosine phosphorylation of SHPS-1 and subsequent association of SHPS-1 with SHP-2, a protein tyrosine phosphatase containing SH2 domains, in Chinese hamster ovary cells overexpressing human EGF receptors. In the cells overexpressing SHPS-1, the tyrosine phosphorylation of SHPS-1 was more evident than that observed in parent cells. However, overexpression of SHPS-1 alone did not affect the activation of MAP kinase in response to EGF. These results suggest that SHPS-1 may be involved in the recruitment of SHP-2 from the cytosol to the plasma membrane in response to EGF.

Animals↗
PubMed1997

Enhancement of the mitogenic effect by artificial juxtacrine stimulation using immobilized EGF.

Mouse epidermal growth factor (EGF) was covalently conjugated with the water-soluble polymer, poly(acrylic acid) (EGF-PAA), or with the water-insoluble polymer, surface-hydrolyzed poly(methyl methacrylate) (EGF-PMMA). Immobilized EGF (EGF-PMMA) stimulated DNA synthesis in Chinese hamster ovary cells overexpressing EGF receptors in amounts that were 5 to 10% of those of free EGF required for comparable effects. In addition, the maximal mitogenic effect of EGF-PMMA was greater than that of unconjugated EGF or EGF-PAA. EGF, EGF-PAA, and EGF-PMMA induced the autophosphorylation of EGF receptors and the stimulation of mitogen-activated protein kinase. However, whereas the onset of these effects was delayed with EGF-PMMA, they persisted for much longer than those of EGF and EGF-PAA. Unlike EGF and EGF-PAA, EGF-PMMA was not associated with cells after their removal from culture and did not induce receptor internalization. Culturing cells with PMMA-immobilized EGF thus represents a model system for studying "juxtacrine" stimulation of cells by membrane-bound growth factors.

Acrylic Resins↗
PubMed1996

Interaction of Shc with adaptor protein adaptins.

The role of Shc as a substrate of receptors for growth factors and cytokines is well established. To gain further insight into the function of Shc in signal transduction, we used an affinity method to identify potential Shc-binding proteins. Incubation of bovine brain lysates with a glutathione S-transferase (GST)-Shc fusion protein immobilized on glutathione-Sepharose beads resulted in the binding of cellular proteins of approximately 115, 110, and 100 kDa as well as those of 50 and 17 kDa. Amino acid sequencing of tryptic peptides revealed that the 100-kDa protein was almost identical to beta-adaptin and that the 110- and 115-kDa proteins were almost identical to alphaA-adaptin. Using immunoblot analysis, anti-alpha-adaptin antibody recognized several proteins of 100 approximately 115 kDa, and anti-beta-adaptin antibody recognized a 100-kDa protein, suggesting that alphaA-, alphaC-, and beta-adaptins are bound to the GST-Shc fusion protein. Immunoblot analysis with anti-alpha-adaptin antibody revealed that alpha-adaptin was coimmunoprecipitated with Shc from PC12, KB, and COS cell lysates, suggesting a specific interaction of Shc and adaptins in intact cells. A binding study using mutant GST-Shc fusion proteins revealed that the collagen homologous region (amino acids 233-377) of Shc was required for adaptin binding. Conversely, the collagen homologous region of Shc inhibited the binding of adaptins to GST-Shc. In addition, adaptin was able to bind mutant fusion proteins containing amino acids 233-369, 233-355, 346-369, and 346-355 of Shc, but failed to bind a mutant containing amino acids 233-345, suggesting that amino acids 346-355 (RDLFDMKPFE) in the collagen homologous region of Shc are required for adaptin binding. Thus, this study indicates the specific interaction of Shc with alpha- and beta-adaptin components of plasma membrane adaptor proteins that are thought to be involved in receptor endocytosis.

Adaptor Protein Complex 2↗
PubMed1996

Tryptophan modulates exocrine secretory function in rat pancreatic acini.

We investigated the effect of tryptophan (Trp) on exocrine secretory function, using isolated rat pancreatic acini. Trp inhibited cholecystokinin-octapeptide (CCK-8)-stimulated amylase secretion, causing a downward shift in the dose-response curve. The inhibitory effect of Trp was dose-dependent and was observed only on the sustained secretion, there being no effect on the initial phase of amylase secretion. Trp (10mM) also inhibited amylase secretion in response to carbachol and bombesin, as well as fluoride, a potent activator of guanine-nucleotide binding proteins. Since Ca2+ influx is necessary for sustained secretion, we examined the effect of Trp on Ca2+ influx and efflux. Trp increased the CCK-8-stimulated Ca2+ influx rate without affecting Ca2+ efflux, suggesting that Trp elevates intracellular Ca2+ levels. Increasing intracellular Ca2+ levels with A23187 resulted in the inhibition of CCK-8-stimulated amylase secretion. These results indicate that Trp inhibits CCK-stimulated sustained amylase secretion, in part by increasing Ca2+ influx into acinar cells.

Amylases↗
PubMed1996

Oral glucose ingestion stimulates cholecystokinin release in normal subjects and patients with non-insulin-dependent diabetes mellitus.

The role of glucose in the regulation of plasma cholecystokinin (CCK) level was investigated in healthy control subjects and patients with non-insulin-dependent diabetes mellitus (NIDDM). Plasma CCK concentration was determined by a specific and sensitive bioassay and by a highly sensitive and reliable double-antibody radioimmunoassay using OAL-656 as an antiserum. In control subjects, ingestion of Trelan G-75 (1,200 mOsm/L,225 mL), which is equivalent to 75 g glucose as metabolic products, caused a rapid and significant increase in plasma CCK bioactivity from 1.3 +/- 0.2 to a peak of 5.8 +/- 0.6 pmol/L and immunoreactive CCK concentration from 1.2 +/- 0.1 to 4.6 +/- 0.6 pmol/L. Ingestion of 75 g glucose in 225 mL water (33.3% solution) increased plasma CCK bioactivity to a similar degree to that observed following Trelan G-75 (peak response, 4.5 +/- 0.4 pmol/L). The same volume of 0.9% NaCl solution or water failed to increase plasma CCK concentration. A smaller dose of glucose (50 b/150 mL water) increased plasma CCK concentration, although the peak level (3.0 +/- 0.5 pmol/L) was less than that observed following 75 g glucose. In patients with NIDDM, Trelan G-75 ingestion increased CCK concentration, but the peak level was lower, albeit insignificantly, than that of normal subjects. When the maximal increment of plasma CCK above the basal value was compared between control and NIDDM subjects, the differences were statistically significant (NIDDM, 3.6 +/- 0.1 pmol/L; control, 5.0 +/- 0.4; P < .01). However, integrated CCK responses to Trelan G-75 in NIDDM (165.8 +/- 15.5 pmol/120 min) were not significantly different from those in control subjects (189.8 +/- 15.9 pmol/120 min). Peak CCK bioactivity occurred within 10 to 30 minutes of ingestion, preceding the increase in glucose and insulin. These results suggest a possible effect of CCK on insulin release in humans, and that the CCK secretory response to glucose in well-controlled diabetic patients is not significantly altered.

Administration, Oral↗
PubMed1996

Ethanol inhibits CCK-induced enzyme secretion by affecting calcium-pump activity in isolated rat pancreatic acini.

The aim of this study was to clarify the effect of ethanol on stimulus-secretion coupling in pancreatic exocrine secretion. We investigated the effects of 600 mM ethanol on cholecystokinin octapeptide (CCK-8)-stimulated amylase release, cytosolic free Ca2+ concentration ([Ca2+]i) and Ca2+ fluxes using in vitro isolated rat pancreatic acini. Ethanol, given alone, stimulated both the initial and the sustained phases of amylase release. On the other hand, ethanol inhibited only the sustained phase of amylase release stimulated by CCK-8. Ethanol also inhibited amylase release in response to fluoride, a direct activator of guanine nucleotide-binding protein, suggesting that ethanol affects intracellular signal transduction molecules. Ethanol had no influences on the initial rise but increased the sustained rise in [Ca2+]i stimulated by CCK-8 and inhibited CCK-8-stimulated Ca2+ outflux without affecting Ca2+ influx. 8-Bromoguanosine 3':5'-cyclic monophosphate, a membrane-permeable analogue of cGMP regulating membrane Ca(2+)-pump activity in various cells, completely reversed the ethanol-induced inhibition of amylase release and Ca2+ outflux in response to CCK-8 as well as fluoride. Given that Ca2+ plays a critical role in stimulus-secretion coupling in pancreatic exocrine secretion, our results indicate that 600 mM ethanol inhibits CCK-8-stimulated amylase release by inhibiting Ca(2+)-pump activity on the plasma membrane.

Amylases↗
PubMed1995

EGF-induced activation of 70-kDa S6 kinase in CHO cells expressing human EGF receptors.

We investigated epidermal growth factor (EGF)-induced activation of 85-kDa/110-kDa phosphatidylinositol (PI)-3-kinase and 70-kDa S6 kinase in Chinese hamster ovary cells expressing the human EGF receptor. EGF-induced activation of p70 S6 kinase was comparable to that induced by insulin, whereas that of PI-3-kinase in anti-phosphotyrosine immunoprecipitates was very small compared with insulin. Wortmannin, a p85/p110 PI-3-kinase inhibitor, inhibited EGF-induced activation of p70 S6 kinase in a dose-dependent manner. Given that several proteins homologous to catalytic subunit of p85/p110 PI-3-kinase have been identified and that wortmannin inhibits distinct form of PI-3-kinase, the present results suggest that wortmannin-sensitive kinases that resemble catalytic subunit of p85/p110 PI-3-kinase may participate in the signaling pathway from EGF receptors to p70 S6 kinase.

Androstadienes↗
PubMed1995

Chronic oral administration of synthetic trypsin inhibitor camostate reduces amylase release from isolated rat pancreatic acini.

In the present study, we examined stimulus-secretion coupling in pancreatic acini prepared from rats given synthetic protease inhibitor camostate at a dose of 200 mg/kg body wt by an orogastric tube once a day for 10 d. Camostate treatment significantly increased pancreatic weight, protein, DNA, and enzyme contents. In acini prepared from the camostate-treated rats, responsiveness to both CCK-8 and carbamylcholine was greatly decreased with no shift in the dose-response curves compared to control acini prepared from saline-treated rats. There were no major changes in the affinity for both high- and low-affinity sites of CCK receptors, but there was a significant reduction in the capacity of low-affinity site based on acinar protein. Responsiveness to secretin in the camostate-treated rat acini was also significantly reduced compared with that in the controls. However, amylase release from the camostate-treated rat acini in response to an increase in intracellular calcium levels induced by the calcium ionophores A23187 or to an increase in intracellular cyclic 3',5'-monophosphate (cyclic AMP) levels caused by 8 bromo cyclic AMP was not significantly different from the control rat acini, suggesting that both Ca(2+)-dependent tyrosine kinase and nucleotide-activated kinases are not impaired. On the other hand, the responsiveness to phorbol ester TPA, which stimulates amylase secretion via a calcium-independent cascade by activating protein kinase C directly, was reduced in the camostate-treated rat acini compared with the controls. These results suggest the possibilities that the reduced amylase secretion in the camostate-treated rats is owing to alterations in both the transmembrane signal transduction and the phosphorylation of regulatory proteins by the Ca(2+)-independent, protein kinase C-dependent mechanisms.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1994

Grb2/Ash binds directly to tyrosines 1068 and 1086 and indirectly to tyrosine 1148 of activated human epidermal growth factor receptors in intact cells.

The activation of receptor tyrosine kinases generates tyrosine-phosphorylated recognition motifs for the binding of signaling proteins containing Src homology 2 domains. We determined the binding sites of Grb2/Ash, an Src homology 2 domain-containing adaptor protein, within epidermal growth factor (EGF) receptors, using Chinese hamster ovary cells overexpressing human EGF receptor mutants in which one of the autophosphorylation sites was retained. In intact cells, the amount of Grb2/Ash coimmunoprecipitated with mutant receptors retaining tyrosines 992, 1068, 1086, 1148, or 1173 was approximately 10, 85, 55, 50, or 20% of wild-type levels, respectively. The association of Grb2/Ash with in vitro autophosphorylated EGF receptor mutants was detectable in those retaining either tyrosines 1068 or 1086 but not in other mutants including those retaining tyrosine 1148. In peptide inhibition assay, phosphorylated peptides representing tyrosines 1068 and 1086 inhibited the binding of Grb2/Ash to in vitro autophosphorylated wild-type EGF receptors, whereas the other peptides representing tyrosines 992, 1148, and 1173 failed to inhibit the binding. Given that tyrosine 1148 of the activated EGF receptor is a major binding site of Shc (Okabayashi, Y., Kido, Y., Okutani, T., Sugimoto, Y., Sakaguchi, K., and Kasuga, M. (1994) J. Biol. Chem. 269, 18674-18678), these results indicate that tyrosines 1068 and 1086 of activated human EGF receptors are direct high affinity binding sites of Grb2/Ash and that tyrosine 1148 is an indirect binding site through Shc in intact cells.

Adaptor Proteins, Signal Transducing↗
PubMed1994

Tyrosines 1148 and 1173 of activated human epidermal growth factor receptors are binding sites of Shc in intact cells.

Autophosphorylation of receptor tyrosine kinases provides binding sites for signaling proteins containing Src homology 2 (SH2) domains. We determined the binding sites of Shc, SH2-containing adaptor protein, within epidermal growth factor (EGF) receptors, using Chinese hamster ovary cells overexpressing EGF receptor mutants in which autophosphorylation sites, either alone or in combination, were replaced by phenylalanine. Binding of Shc to EGF receptor mutants lacking single tyrosine residues at 1148 or 1173 decreased by approximately 60 or approximately 15%, respectively, whereas other single point mutants bound the wild-type level of Shc. Binding of Shc markedly decreased in mutants lacking both tyrosine residues at 1148 and 1173. In peptide inhibition assay, phosphorylated nonameric peptide representing tyrosine 1148, DNPDpYQQDF, but not pentameric peptide, pYQQDF, inhibited the binding of glutathione S-transferase-Shc SH2 domain fusion protein to in vitro autophosphorylated EGF receptors, suggesting that N-terminal sequences adjacent to phosphotyrosine are necessary for the association of Shc. Based on results of peptide inhibition assays in which phosphorylated peptides representing tyrosines 992, 1148, and 1173 inhibited Shc binding to the receptor, we constructed another EGF receptor mutant in which one of these tyrosine residues was retained. The amount of Shc bound to mutant receptors retaining tyrosines 1148, 1173, or 992 was approximately 80, approximately 40, or approximately 10% of wild-type level, respectively. These results indicate that tyrosine 1148 of activated human EGF receptors is a major binding site of Shc and tyrosine 1173 is a secondary binding site in intact cells.

Amino Acid Sequence↗
PubMed1994

Signal transduction pathways from insulin receptors to Ras. Analysis by mutant insulin receptors.

We have examined the involvement of insulin receptor (IR) substrate-1 (IRS-1) and/or Shc in the upstream of Ras activation in insulin signaling using Chinese hamster ovary (CHO) cell lines overexpressing wild-type (CHO-IR) cells) or mutant insulin receptors. In CHO-IR cells, insulin rapidly phosphorylated IRS-1 and Shc at tyrosine residues and stimulated the formation of the active GTP-bound Ras (Ras.GTP). In contrast, a CHO cell line overexpressing the kinase-negative mutant insulin receptor substituting Arg1018 for Lys1018 was unable to tyrosine-phosphorylate IRS-1 and Shc and failed to activate Ras in response to insulin. A CHO cell line overexpressing the mutant insulin receptor, substituting Ala960 for Tyr960 and which was known to exhibit impaired tyrosine phosphorylation of IRS-1 and biological effects evoked by insulin, showed severely impaired insulin-dependent tyrosine phosphorylation of Shc and moderately impaired activation of Ras. Another cell line overexpressing the mutant insulin receptor, lacking 82 amino acids of the C terminus of beta-subunit and which was recently reported to retain normal insulin-dependent tyrosine phosphorylation of IRS-1, showed slightly impaired Ras activation at 10(-7) M insulin with severely reduced tyrosine phosphorylation of Shc protein. Furthermore, insulin did not induce the association of tyrosine-phosphorylated IRS-1 and Shc in CHO-IR cells. These results suggest that Shc and IRS-1 lie in the separate signaling pathways and that the tyrosine phosphorylation of IRS-1 with or without some low level of Shc phosphorylation may be enough to stimulate the submaximal accumulation of Ras.GTP complex and may need synergistically the higher level of tyrosine phosphorylation of Shc to induce the full activation of Ras in insulin signaling.

Animals↗
PubMed1994

Potentiating effect of insulin on exocrine secretory function in isolated rat pancreatic acini.

BACKGROUND/AIMS: Insulin is shown to exert various regulatory effects on the exocrine pancreatic function. We investigated the direct effect of insulin on exocrine pancreatic secretion. METHODS: The effects of insulin on amylase release, 125I-secretin binding and Na(+)- and K(+)-activated adenosine triphosphate phosphohydrolase (Na+,K(+)-ATPase) activity were measured using the isolated rat pancreatic acini. RESULTS: Insulin potentiated the amylase release elicited by secretin plus cholecystokinin (CCK), but not by either secretin or CCK alone. The potentiating effect of insulin was dependent on the concentration and preincubation time. Insulin had no effect on 125I-secretin binding. Ouabain, a specific Na+,K(+)-ATPase inhibitor, caused a concentration-dependent inhibition of the potentiated secretion by insulin without affecting the secretory response to secretin plus CCK. In membranes prepared from acini treated with insulin, Na+,K(+)-ATPase activity was significantly increased. Similar results were obtained when acini were treated with insulin in combination with secretin plus CCK. CONCLUSIONS: Insulin exerts a direct effect on pancreatic acinar cells and potentiates exocrine secretion elicited by secretin in combination with CCK, in part, by increasing Na+,K(+)-ATPase activity.

Amylases↗
PubMed1993

Effect of islet hormones on secretin-stimulated exocrine secretion in isolated perfused rat pancreas.

To clarify the effect of islet hormones on pancreatic ductular cell function, we measured the exocrine secretion elicited by 10 pM secretin in the presence or absence of islet hormones using an isolated perfused rat pancreas model. Insulin significantly increased secretin-stimulated pancreatic juice secretion, but not protein secretion. The potentiating effect of insulin on pancreatic juice secretion was concentration-dependent, and the maximal effect was observed with 1 microM insulin. Ouabain, a specific Na+,K(+)-ATPase inhibitor, caused concentration-dependent inhibition of the potentiating effect of insulin without affecting secretin action. Glucagon (100 nM) significantly inhibited secretin-stimulated pancreatic juice secretion and also tended to inhibit protein secretion. A somatostatin analog, SMS 201-995 (10 nM) significantly inhibited both the pancreatic juice and protein secretion stimulated by secretin. The inhibitory effect of SMS 201-995 was concentration-dependent and was maximal at 1-10 nM. These results demonstrate that insulin potentiates the secretory response to secretin, at least partly by increasing Na+,K(+)-ATPase activity, whereas glucagon and somatostatin inhibit this response. Thus, pancreatic islet hormones regulate the secretory function of pancreatic ductular and centroacinar cells.

Animals↗
PubMed1993

Role of endogenous bile on basal and postprandial CCK release in humans.

The role of intraduodenal bile in regulation of plasma cholecystokinin (CCK) levels were investigated in patients with obstructive jaundice under external bile diversion and under physiological bile flow into the duodenum by internal bile drainage. Basal plasma CCK levels determined by a specific and sensitive bioassay in patients under external bile drainage (2.2 +/- 0.2 pmol/liter; mean +/- SE) were significantly higher than those in control subjects (1.0 +/- 0.3 pmol/liter). In control subjects, the peak CCK response (6.2 +/- 0.7 pmol/liter) to a test meal was seen at 45 min, whereas that in patients under external bile drainage, it was seen at 20 min after a test meal (17.6 +/- 3.2 pmol/liter; P < 0.01 vs controls). After peak response, plasma CCK levels in controls gradually decreased, but remained significantly elevated during a 3-hr observation period. In patients under bile diversion, the test meal caused a prompt plasma CCK peak, with a transient fall followed by a continuous rise until 180 min postprandially. In six patients, external bile diversion was changed to internal biliary drainage with a stent tube within two weeks to maintain physiological bile flow into the duodenum. Internal bile drainage normalized basal (0.9 +/- 0.2 pmol/liter) as well as meal-stimulated CCK release (peak value: 5.0 +/- 0.8 pmol/liter). These results demonstrate that endogenous bile exerts tonic inhibition on basal and postprandial plasma CCK levels in humans.

Adenoma, Bile Duct↗
PubMed1993

In vitro inhibitory effect of somatostatin on secretin action in exocrine pancreas of rats.

BACKGROUND: Exocrine pancreatic function is influenced by pancreatic islet hormones. Although the existence of somatostatin receptors has been shown on pancreatic acinar cells, the in vitro effect of somatostatin on exocrine secretory function has not been established. METHODS: Using isolated rat pancreatic acini, the effect of somatostatin analog SMS 201-995 (SMS) and somatostatin 14 (S-14) on amylase release, cyclic adenosine monophosphate (cAMP) production, and hormone binding were determined. RESULTS: SMS inhibited the potentiating effect of secretin on amylase response to cholecystokinin octapeptide (CCK-8) in a concentration-dependent manner. The inhibitory effects of SMS and S-14 were similar on a molar basis and were observed when vasoactive intestinal polypeptide (VIP) but not 8bromoadenosine 3':5' cyclic monophosphate was used instead of secretin and when carbachol, bombesin, A23187, and 12-O-tetradecanoylphorbol 13-acetate were used instead of CCK-8. SMS inhibited secretin-induced cAMP production, and the dose-inhibition curve for cAMP was similar to that for amylase release. SMS had no influence on 125I-secretin and 125I-VIP binding. CONCLUSIONS: Somatostatin acts directly on acinar cells and inhibits secretin potentiation of secretory response in part by inhibiting secretin-induced cAMP production.

8-Bromo Cyclic Adenosine Monophosphate↗