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R T Jensen

Publications and source records attributed to R T Jensen.

At least 163 records · Page 9Linked to original sources
PubMed1994

Adrenocorticotropic hormone--secreting islet cell tumors: are they always malignant?

PURPOSE: To evaluate the frequency with which benign occult islet cell tumors cause ectopic adrenocorticotropic hormone (ACTH) syndrome. MATERIALS AND METHODS: Ten patients with Cushing syndrome due to the production of ACTH by a pancreatic islet cell tumor were studied. In addition, 53 cases of ACTH-secreting islet cell tumors in the English-language literature were reviewed. RESULTS: All 10 of the authors' patients had malignant islet cell tumors. Liver metastases were present in all 10 patients at presentation. Five patients are dead, four patients are alive with liver metastases, and one patient is alive without gross evidence of residual tumor after distal pancreatectomy and right hepatectomy. Eight of the 10 islet cell carcinomas produced gastrin in addition to ACTH. In the 53 reported cases of ectopic ACTH production, there was only one benign adenoma with a prolonged follow-up. CONCLUSION: When ectopic ACTH production is caused by an islet cell tumor, the tumor is large and malignant and has usually metastasized to the liver by the time Cushing syndrome is diagnosed. No occult ACTH-producing islet cell tumor was encountered in the authors' experience or in a review of the literature.

ACTH Syndrome, Ectopic↗
PubMed1994

Thapsigargin defines roles of Ca2+ in initial, sustained, and potentiated stimulation of pepsinogen secretion.

The roles of Ca2+ in agonist-induced pepsinogen secretion from guinea pig chief cells remain unclear. We used cholecystokinin octapeptide (CCK-8) or secretin alone or with thapsigargin (TG) to clarify these roles. TG releases Ca2+ from intracellular stores by inhibiting microsomal Ca(2+)-adenosinetriphosphatase (ATPase), thereby depleting intracellular Ca2+ (Cai2+) stores. In most cells TG also causes Ca2+ influx. In the present study, with an extracellular Ca2+ concentration ([Ca2+]o) of 1.5 mM, CCK-8 (0.1 microM) caused a rapid increase in pepsinogen secretion; however, the rate decreased with time. With [Ca2+]o = 0, the initial increase was similar but later secretion was abolished, suggesting that Ca2+ influx was important for sustained secretion. With [Ca2+]o = 1.5 mM, TG (0.1 microM) caused a 2.7-fold sustained increase in in Cai2+ concentration ([Ca2+]i) and a ninefold sustained increase in pepsinogen secretion. With [Ca2+]o = 0, TG caused a transient 66% increase in [Ca2+]i and a 50% increase in pepsinogen secretion. The time course of TG-induced pepsinogen secretion correlated with the time course of TG-induced increases in [Ca2+]i. These data demonstrated that Ca2+ influx itself was a potent stimulant of pepsinogen secretion. We further focused on the roles of increasing [Ca2+]i from Cai2+ stores. With or without extracellular Ca2+ (Cao2+) present, addition of CCK-8 (0.1 microM) 10 min after TG caused no further increase in [Ca2+]i, demonstrating depletion of the inositol 1,4,5-trisphosphate-sensitive pool. The Ca(2+)-mobilizing agent CCK-8 caused no pepsinogen secretion 10 min after TG preincubation, demonstrating that mobilization of Ca2+ from intracellular stores was important in the rapid initial phase stimulation of pepsinogen secretion caused by CCK-8. In contrast, preincubation with TG had no effect on pepsinogen secretion by secretin, an agent that increases adenosine 3',5'-cyclic monophosphate. A 6-min preincubation with TG potentiated the subsequent stimulation of pepsinogen secretion caused by secretin in the presence of Cao2+ where [Ca2+]i remained elevated. However, TG-induced potentiations of secretin-stimulated pepsinogen secretion was abolished once [Ca2+]i had returned to the basal level in the absence of Cao2+.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Gastric smooth muscle cells possess two classes of endothelin receptors but only one alters contraction.

Endothelin (ET)-like immunoreactivity and ET binding sites are widely distributed in the gastrointestinal tract, and ET causes contraction of stomach muscle strips. To determine whether ETs could interact with gastric smooth muscle cells directly and alter function, we measured binding of 125I-ET-1, 125I-ET-2, and 125I-ET-3 to dispersed gastric smooth muscle cells from guinea pig and their abilities to alter cell length. Each ligand bound in a time- and temperature-dependent manner, which was specific and saturable. Analysis of the dose-inhibition curves of both ET-1 and ET-3 for binding of each ligand indicated the presence of two classes of receptors, one class (ETA receptor) with a high affinity for ET-1 and ET-2 but a low affinity for ET-3, and the other (ETB receptor) with a high affinity for ET-1, ET-2, and ET-3. The ligands were rapidly internalized by both receptors; however, it was greater with ETA receptors. ET-1 stimulated muscle contraction (50% effective concentration approximately 2 nM), whereas ET-3 did not stimulate contraction or cause relaxation. These results demonstrate that gastric smooth muscle cells possess two classes of ET receptors. One type (ETA) has a high affinity for ET-1 and ET-2 and a low affinity for ET-3, and receptor occupation results in rapid ligand internalization and muscle contraction; the other type (ETB) has a high affinity for ET-1, ET-2, and ET-3, and receptor occupation results in a lesser degree of ligand internalization than the ETA receptor and does not alter contractile behavior.

Animals↗
PubMed1994

Chief cells possess somatostatin receptors regulated by secretagogues acting through the calcium or cAMP pathway.

Inhibition both in vivo and in vitro of pepsinogen secretion by somatostatin (SS) and the histological demonstration that fundic D-cells contain long cytoplasmic processes extending to chief cells suggest a possible direct effect of SS on chief cell function. The aim of the present study was to determine whether SS interacts directly with receptors on isolated gastric chief cells and, if so, how SS alters cell function. Binding of 125I-[Tyr11]SS14 to chief cells was saturable, time and temperature dependent, and was inhibited by both SS14 (Ki 1.6 nM) and SS28 (Ki 5.2 nM). SMS-201-995 was 1,300-fold less potent than SS14. Calcium-mobilizing secretagogues reduced binding of 125I-[Tyr11]SS14 with efficacies of cholecystokinin octapeptide (CCK-8) > carbachol > gastrin. Adenosine 3',5'-cyclic monophosphate (cAMP)-activating secretagogues also inhibited binding with efficacies of secretin > vasoactive intestinal polypeptide (VIP). 12-O-tetradecanoylphorbol 13-acetate (TPA) or A-23187 also decreased binding. Analyses demonstrated that CCK-8 and TPA were decreasing the affinity of SS receptors for 125I-[Tyr11]SS14 without affecting their binding capacity. Both SS14 and SS28 at a maximally effective concentration inhibited cAMP production caused by VIP or secretin (20-30%) but did not alter cytosolic calcium ([Ca2+]i), inositol phosphates, or pepsinogen release. We conclude that chief cells possess SS receptors with a high affinity for both SS14 and SS28 but low affinity for SMS-201-995 and thus resemble the SSB receptors described in the rat cerebral cortex. Although occupation of these receptors by SS has no effect on pepsinogen release induced by secretagogues acting through either the calcium or the cAMP pathway, SS receptor occupation is regulated by agents activating phospholipase C, adenylate cyclase, protein kinase C, and [Ca2]i.

Animals↗
PubMed1994

Smooth muscle cells from guinea pig stomach possess high-affinity galanin receptors that mediate relaxation.

Galanin-like immunoactivity occurs in nerves and plexi in muscle layers throughout gastrointestinal tract including the stomach. Galanin can affect gastric emptying and contraction or relaxation of gastric muscle in different species. The aim of this study was to investigate the direct effect of galanin on dispersed gastric smooth muscle cells and to characterize any galanin receptors that mediated any effect. Dispersed gastric smooth muscle cells were prepared from guinea pig stomach by collagenase digestion. Porcine galanin (p-galanin; 1 microM) did not stimulate contraction when present alone; however, p-galanin (1 microM) inhibited carbachol-induced contraction with a half-maximal effect at 7 nM. p-Galanin (1 microM) increased cellular adenosine 3',5'-cyclic monophosphate (cAMP) content by 10 s and caused a maximal increase of 80% over basal. 125I-galanin (porcine) bound to dispersed cells in a time- and temperature-dependent manner. Binding was saturable, reversible, and specific. Binding of 125I-galanin was inhibited almost equally by porcine and rat galanin (Ki = 6-8 nM) but was not inhibited by the galanin-associated peptide [preprogalanin-(108-123)]. The fragment galanin-(1-16) was equally potent to rat galanin; however, the fragment galanin-(9-29) was 56-fold less potent (Ki = 370 nM). Computer analysis demonstrated there were two binding sites for p-galanin on gastric smooth muscle cells, a high-affinity site (Kd = 2.6 nM) with low capacity (Bmax = 175 fmol/mg protein) and a low-affinity site (Kd = 150 nM) with large capacity (Bmax = 3,611 fmol/mg protein).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Internalization of the gastrin-releasing peptide receptor is mediated by both phospholipase C-dependent and -independent processes.

Consequent to agonist exposure, many G protein-coupled receptors undergo sequestration or internalization. Results with receptors linked to adenylate cyclase, such as the beta 2-adrenergic receptor, or receptors linked to phospholipase C (PLC) have provided conflicting results regarding the role of second messenger-dependent (i.e., protein kinase A or C) and -independent (i.e., beta-adrenergic receptor kinase) kinases in mediating this process. Recent results for truncated and mutated gastrin-releasing peptide (GRP) receptors (GRP-R), as well as muscarinic cholinergic receptors, suggest that activation of protein kinase C may be needed for full receptor internalization. Nearly all G protein-coupled receptors studied to date, including the GRP-R, possess two highly conserved amino acids that are important in mediating receptor-G protein coupling to second messengers, i.e., arginine in the proximal second intracellular loop and alanine in the distal third intracellular loop. We selectively mutated each of these residues in the GRP-R to determine their importance for activation of PLC. Site-directed mutagenesis was performed to change arginine at position 139 to glycine (R139G mutant) and alanine at position 263 to glutamate (A263E mutant), with stable cell lines being created by transfection of the wild-type or mutated receptor cDNA into BALB/3T3 fibroblasts. Both R139G (Kd = 12.0 +/- 1.6 nM) and A263E (Kd = 12.2 +/- 1.7 nM) had a lower affinity for bombesin than did wild-type GRP-R (Kd = 1.4 +/- 0.4 nM); however, characteristic stoichiometries for the binding of agonists to this receptor were maintained equally in all three cell lines (bombesin > GRP >> neuromedin B). The wild-type GRP-R exposed to bombesin increased [3H]inositol phosphates (a measure of PLC activation) approximately 4-fold, with an EC50 of 5.1 +/- 2.2 nM. In contrast, [3H]inositol phosphates were not significantly increased in cells expressing R139G or A263E receptors, demonstrating that Arg139 and Ala263 are required for GRP-R activation of PLC. However, when receptor internalization at 37 degrees was assessed by ligand acid-stripping studies, 53 +/- 2% of A263E receptors were internalized at 90 min, compared with 85 +/- 5% of wild-type GRP-R, whereas only 10 +/- 3% of R139G receptors were internalized. Preincubation of either mutant cell line with 100 nM 12-O-tetradecanoylphorbol-13-acetate markedly increased internalization rates, such that at 90 min 62 +/- 2% of R139G receptors and 82 +/- 1% of A263E receptors were internalized.(ABSTRACT TRUNCATED AT 400 WORDS)

Alanine↗
PubMed1994

Apparent lymph node primary gastrinoma.

BACKGROUND: The existence of lymph node (LN) primary gastrinoma as a cause of Zollinger-Ellison syndrome is controversial. We reviewed our experience with patients in whom gastrinomas were identified and excised only from LNs. METHODS: From 1982 to 1992, 110 patients with ZES underwent exploration for gastrinoma and 21 (19%) had disease limited to one or more LNs. Standardized exploration included intraoperative ultrasonography, intraoperative endoscopy with transillumination and exploratory duodenotomy in 86%, 67%, and 24% of patients, respectively. Each patient underwent yearly biochemical and radiologic follow-up. RESULTS: Thirteen patients (62%) with a median follow-up period of 5.8 years had an initial biochemical cure, whereas eight patients (38%) with a median follow-up period of 3.6 years had persistent disease. Of the 13 patients whose condition initially returned to normal, four have had biochemical recurrence, with a median time to recurrence of 4.2 years and a median follow-up period of 7.4 years. Nine patients (43%) remain biochemically cured, with a median follow-up period of 5.3 years. CONCLUSIONS: Resection of apparent LN primary gastrinoma is warranted, because 43% of those who underwent resection had no evidence of disease, with a median follow-up period of 5.3 years.

Adult↗
PubMed1994

Gastrin-releasing peptide receptor-induced internalization, down-regulation, desensitization, and growth: possible role for cyclic AMP.

Stimulation of the gastrin-releasing peptide receptor (GRP-R) in Swiss 3T3 cells resembles that of a number of other recently described G protein-coupled receptors, insofar as both the phospholipase C and adenylyl cyclase signal transduction pathways are activated. GRP-R activation induces numerous alterations in both the cell and the receptor, but because two signal transduction pathways are activated it is difficult to determine the specific contributions of either pathway. We have found that BALB/3T3 fibroblasts transfected with the coding sequence for the GRP-R are pharmacologically indistinguishable from native receptor-expressing cells and activate phospholipase C in a manner similar to that of the native receptor but fail to increase cAMP in response to bombesin; thus, they may be useful cells to explore the role of activation of each pathway in altering cell and receptor function. Swiss 3T3 cells and GRP-R-transfected BALB/3T3 cells expressed identically glycosylated receptors that bound various agonists and antagonists similarly. G protein activation, as determined by evaluation of agonist-induced activation of phospholipase C and by analysis of the effect of guanosine-5'-(beta,gamma-imido)triphosphate on GRP-R binding affinity, was indistinguishable. Agonist stimulation of GRP-R caused similar receptor changes (internalization and down-regulation) and homologous desensitization in both cell types. Bombesin stimulation of Swiss 3T3 cells that had been preincubated with forskolin increased cAMP levels 9-fold, but no bombesin-specific increase in cAMP levels was detected in transfected cells, even though forskolin and cholera toxin increased cAMP levels in these cells. Quiescent Swiss 3T3 cells treated with bombesin rapidly increased c-fos mRNA levels and [3H]thymidine incorporation, whereas both effects were potentiated by forskolin. The specific protein kinase A inhibitor H-89 blocked increases in c-fos levels and [3H]thymidine incorporation induced by low concentrations of bombesin. GRP-R-transfected BALB/3T3 cells increased c-fos mRNA levels and [3H]thymidine incorporation with the addition of serum but not bombesin. These data suggest that bombesin-stimulated increases in cellular levels of cAMP appear not to be an important mediator of GRP-R internalization, down-regulation, or desensitization but do play an important role in bombesin-induced mitogenesis.

3T3 Cells↗
PubMed1993

Serines and threonines in the gastrin-releasing peptide receptor carboxyl terminus mediate internalization.

Most seven-transmembrane G-protein-coupled receptors are rapidly internalized after binding agonist, but the general amino acid recognition sequences mediating this phenomenon have not been identified. In this study, components of the gastrin-releasing peptide receptor (GRP-R) regulating internalization were identified. Four GRP-R mutants with stop codons placed at variable distances distal to the putative palmitoylation sites Cys340-341 were transiently expressed in CHOP fibroblasts. A construct with a minimal carboxyl tail deletion, T375, bound and internalized agonist similarly to wild type receptor. Progressively larger truncations of the carboxyl terminus, however, increasingly impaired GRP-R-mediated internalization without altering receptor-agonist affinity. Three additional constructs were created: one with the putative palmitoylation sites replaced with Ala (CC340-341AA), one with the carboxyl-terminal protein kinase C-consensus sequence converted to Ala (TS360-361AA), and one with all Ser and Thr distal to Cys341 converted to Ala, Asn, or Gly (JF1). All constructs bound agonist similarly to wild type receptor. CC340-341AA internalized similarly to native receptor (93 +/- 3% of wild type by 60 min), whereas internalization of TS360-361AA was partially attenuated (64 +/- 2% of wild type by 60 min). JF1, however, internalized as poorly as T346, with only 16 +/- 2% of the wild type receptors internalized by 60 min. To assess G-protein coupling, selected receptor constructs were stably transfected into Balb fibroblasts, and phosphoinositol hydrolysis was determined. The largest GRP-R truncation, T346, increased total inositol phosphates (EC50 = 2.9 +/- 0.9 nM) similarly to wild type receptor (EC50 = 5.1 +/- 2.2 nM), as did CC340-341AA (EC50 = 5.4 +/- 1.5 nM) and TS360-361AA (EC50 = 3.1 +/- 1.2 nM). These data demonstrate that the multiple Ser and Thr located within the GRP-R carboxyl terminus distal to Cys341, including but not limited to those within the protein kinase C-consensus sequence, specifically regulate GRP-R internalization rates independent of receptor-G-protein coupling.

Amino Acid Sequence↗
PubMed1993

Assessment and prediction of long-term cure in patients with the Zollinger-Ellison syndrome: the best approach.

OBJECTIVE: To identify the best method for determining freedom from disease after gastrinoma resection and for predicting long-term disease-free status in patients with the Zollinger-Ellison syndrome. DESIGN: Prospective study in consecutive patients. SETTING: Referral-based clinical research center. PATIENTS: Eighty-one consecutive patients with the Zollinger-Ellison syndrome who underwent surgical exploration for gastrinoma resection. INTERVENTION: Patients were evaluated after gastrinoma resection, before discharge, 3 to 6 months after surgery, and yearly thereafter. Evaluation included secretin provocative testing and fasting serum gastrin determinations. Follow-up examinations after the initial postoperative evaluations included a clinical assessment, acid secretion studies, a calcium provocative test, and various imaging studies. MEASUREMENTS AND MAIN RESULTS: Most patients (96%) had gastrinomas. Freedom from disease was defined by improved symptoms, reduced acid output and antisecretory drug requirements, and a normal gastrin level, normal imaging studies, and negative gastrin provocative studies. Fifty-two percent of patients (n = 42) were disease-free immediately after surgery, 44% at 3 to 6 months, 42% at 1 year, and 35% by 5 years (mean follow-up, 39 months). The secretin provocative test was the first test to become positive in 45% of patients with a recurrence, the serum gastrin determination was the first test to become positive in 36%, and both tests became positive at the same time in 18%. No recurrence was first detected by imaging studies or by calcium provocative testing. Fasting serum gastrin levels and secretin provocative test results at different postoperative times can be used to predict the probability of a patient remaining disease free at 3 years. Patients with a normal gastrin level and a normal secretin provocative test immediately after surgery had a 3-year disease-free probability of 75%, and normal results on both tests at 6 months, 1 year, and 2 years yielded respective probabilities of 88%, 95%, and 100%. CONCLUSIONS: Both the secretin provocative test and fasting serum gastrin determination are necessary for the early diagnosis of cases of recurrent disease after gastrinoma resection. The calcium provocative test and imaging studies do not detect any recurrences first. Fasting serum gastrin determinations and secretin provocative testing at different postoperative times can be used to predict the probability of a patient remaining disease free at 3 years.

Adult↗
PubMed1993

The fifth transmembrane segment of the neuromedin B receptor is critical for high affinity neuromedin B binding.

The two bombesin receptor subtypes, neuromedin B (NMB-R) and gastrin releasing peptide (GRP-R) receptors, bind their respective ligands with high affinity. To identify molecular components mediating high affinity NMB binding, four mutant receptors were constructed, in which different parts of the NMB-R were replaced with the corresponding regions of the GRP-R. When stably expressed in Balb 3T3 fibroblasts, all four NMB-R/GRP-R chimeras were functional and showed NMB-induced stimulation of inositol phosphate (IP) formation. Results of 125I-[D-Tyr0]NMB displacement assays using unlabeled NMB for competition indicated that high affinity NMB binding was determined by amino acid sequences in transmembrane domain V (TM-V) of the NMB-R. To identify which amino acid(s) in TM-V of NMB-R contributed to high affinity NMB binding, four additional NMB-R mutants were constructed where non-conserved amino acids in TM-V of NMB-R were replaced by the corresponding GRP-R amino acids. Three of the mutations, TyrPheLeu220-222-->PheTyrVal, Ile230-->Val, and His234-->Phe, did not affect high affinity NMB binding. The Ile216-->Ser substitution, however, abolished high affinity NMB binding and severely impaired the ability of the mutant receptor to stimulate NMB-dependent inositol phosphate formation. These results suggest that ILe216 in TM-V of NMB-R may be critical for high affinity NMB binding.

3T3 Cells↗
PubMed1993

Human small cell lung cancer cell lines express functional atrial natriuretic peptide receptors.

Small cell lung cancer cell (SCLC) lines, NCI-H82, NCI-H660, and NCI-H1284, and HeLa cells were analyzed for the presence of atrial natriuretic peptide (ANP) receptors. In these SCLC cell lines and HeLa cells, ANP A receptor mRNA was identified by Southern blot analyses of polymerase chain reaction products and RNase protection assays using poly(A)(+)-selected RNA. Saturable binding assays revealed that HeLa cells had 2000 to 5000 high affinity atrial natriuretic peptide receptors per cell with a dissociation constant of 140 pM. In the SCLC cell lines, the binding was saturable but too low to accurately estimate the number of binding sites. After addition of human ANP, radioimmunoassays revealed accumulation of cyclic GMP in SCLC cells as well as HeLa cells in a dose-dependent fashion. The half-maximal stimulation concentration of cyclic GMP accumulation in HeLa and these SCLC cell lines was approximately 2 nM. Tetrazolyl blue assays and tritiated thymidine incorporation did not show any remarkable growth inhibition or growth stimulation of SCLC cell lines after addition of human ANP up to 3.3 microM, more than 1000-fold greater than the half-maximal stimulation concentration of cyclic GMP accumulation. Our results indicate that human SCLC cells express functional ANP receptors but ANP addition produced no detectable change in their growth pattern.

Atrial Natriuretic Factor↗
PubMed1993

A newly recognized action of cholecystokinin on pancreatic acini-release of lactate dehydrogenase.

In the course of examining the actions of the cholecystokinin octapeptide (CCK-8) on pancreatic acini we found that CCK-8 can stimulate release of the large-molecular-weight cytoplasmic protein, lactate dehydrogenase (LDH) by as much as 6-fold. CCK-8-stimulated LDH release is mediated by a CCK-preferring receptor, detectable at 100 pM CCK-8, maximal at 100 nM CCK-8, constant for up to 30 min, reversible, not desensitized, and dependent on oxidative metabolism and incubation temperature but not on calcium in the extracellular medium. This action of CCK-8 is blocked by inhibitors of protein kinases, staurosporine, H-7, H-8 and H-9, but not by calmodulin antagonists, chlorpromazine, trifluoperazine or W-7. This action of CCK-8 on LDH release is not reproduced by TPA, 8Br-cAMP or A23187. Thus, it appears to be mediated by a previously uncharacterized protein kinase or an isoform of protein kinase C that is not maximally stimulated by TPA.

Alkaloids↗
PubMed1993

Bombesin receptor antagonists differentiate receptor subtypes in rat brain.

Previous studies have shown that various bombesin receptor antagonists can distinguish between bombesin receptor subtypes in peripheral tissues. To determine whether these antagonists would be useful in differentiating bombesin receptor subtypes in the rat central nervous system, we used in vitro receptor autoradiography to examine the binding affinities of several bombesin receptor antagonists for two brain regions we had characterized as possessing distinct bombesin receptor subtypes. Our results demonstrate that, consistent with peripheral bombesin receptors, bombesin receptor subtypes in the rat brain can be differentiated by various bombesin receptor antagonists.

Animals↗
PubMed1993

Occupation of low-affinity cholecystokinin (CCK) receptors by CCK activates signal transduction and stimulates amylase secretion in pancreatic acinar cells.

Based on the effects of monensin on binding of 125I-CCK-8 and its lack of effect on CCK-8-stimulated amylase secretion we previously proposed that pancreatic acinar cells possess three classes of CCK receptors: high-affinity receptors, low-affinity receptors and very low-affinity receptors [1]. In the present study we treated pancreatic acini with carbachol to induce a complete loss of high-affinity CCK receptors and then examined the action of CCK-8 on inositol trisphosphate IP3(1,4,5), cytosolic calcium and amylase secretion in an effort to confirm and extend our previous hypothesis. We found that first incubating pancreatic acini with 10 mM carbachol decreased binding of 125I-CCK-8 measured during a second incubation by causing a complete loss of high-affinity CCK receptors with no change in the low-affinity CCK receptors. Carbachol treatment of acini, however, did not alter the action of CCK-8 on IP3(1,4,5), cytosolic calcium or amylase secretion or the action of CCK-JMV-180 on amylase secretion or on the supramaximal inhibition of amylase secretion caused by CCK-8. The present findings support our previous hypothesis that pancreatic acinar cells possess three classes of CCK receptors and suggest that high-affinity CCK receptors do not mediate the action of CCK-8 on enzyme secretion, that low-affinity CCK receptors may mediate the action of CCK on cytosolic calcium that does not involve IP3(1,4,5) and produce the upstroke of the dose-response curve for CCK-8-stimulated amylase secretion and that very low-affinity CCK receptors mediate the actions of CCK on IP3(1,4,5) and cytosolic calcium and produce the downstroke of the dose-response curve for CCK-8-stimulated amylase secretion. Moreover, CCK-JMV-180 is a full agonist for stimulating amylase secretion by acting at low-affinity CCK receptors and is an antagonist at very low-affinity CCK receptors.

Amylases↗
PubMed1993

Ligand binding, internalization, degradation and regulation by guanine nucleotides of bombesin receptor subtypes: a comparative study.

Recent cloning studies confirm two subtypes of Bn receptors exist, a neuromedin B-preferring receptor (NMB-R) and a gastrin-releasing peptide-preferring receptor (GRP-R). Both subtypes occur widely in GI tract and the CNS; however, in contrast to the GRP-R subtype little is known about the ligand-receptor interactions for the NMB-R. Therefore, in the present study we explored the ligand-receptor interactions including kinetics, stoichiometry, internalization, degradation and regulation by guanine nucleotide binding proteins with the NMB-R and compared it to the GRP-R. The rat glioblastoma C-6 cell line which possess functional NMB-R and 3T3 cells which possess functional GRP-R were used. 125I-[D-Tyr0]NMB and 125I-[Tyr4]Bn were prepared using Iodogen and purified on HPLC. At 37 degrees C binding of 125I-[D-Tyr0]NMB to NMB-R or 125I-[Tyr4]Bn to GRP-R was maximal by 5-15 min and decreased to 60-70% after 60 min. HPLC analysis of the 60 min supernatant showed that > 80% of each tracer was degraded. Addition of proteinase inhibitors had a varied inhibitory effect on degradation with the relative order of potency in C-6 cells being leupeptin > bacitracin < chymostatin > phosphoramidon >> bestatin and amastatin and 3T3 cells being bacitracin = phosphoramidon > leupeptin = bestatin > chymostatin > amastatin in 3T3 cells. By HPLC analysis addition of bacitracin prevented the degradation in both cell types. With both receptor subtypes dissociation of bound radioligands was slow, with 70-80% of either 125I-[D-Tyr0]NMB or 125I-[Tyr4]Bn remained cell-associated after 60 min suggesting possible peptide internalization. With an acid wash procedure to remove surface bound radioligands, 60% of the C-6 cell-associated 125I-[D-Tyr0]NMB and 52% of the 3T3 cell-associated 125I-[Tyr4]Bn were internalized after 30 min at 37 degrees C. With membranes from cells possessing either receptor subtype, the stable guanine nucleotide GPP(NH)P inhibited in a dose-dependent fashion binding of ligands. Computer analysis demonstrated that GPP(NH)P decreased receptor affinity for ligands to both receptor subtypes. These results demonstrated that NMB receptors, similar to GRP receptors and rapidly internalize bound agonists and rapidly degrade agonists. The ligand-receptor interaction is regulated by a guanine nucleotide binding protein for both Bn receptor subtypes.

Animals↗
PubMed1993

Prospective comparative study of ability of MR imaging and other imaging modalities to localize tumors in patients with Zollinger-Ellison syndrome.

The role of magnetic resonance (MR) imaging in patients with pancreatic endocrine tumors such as Zollinger-Ellison syndrome (ZES) is controversial. In the present study we have examined the ability of current MR imaging compared with other imaging modalities, to localize gastrinomas in 43 patients with ZES. All results were subsequently assessed at exploratory laparotomy (N = 34) or by liver biopsy (N = 9). For the 18 patients with metastatic gastrinoma in the liver, MR imaging had a sensitivity of 83%, ultrasound 50%, CT 56%, and angiography 61%. The combination of MR imaging, ultrasound, and CT were the same as MR imaging alone. For MR imaging, both T1 and STIR sequences had equal sensitivity, although tumors were more easily seen with STIR sequences. Specificity of MR imaging was slightly lower (88%) than the other modalities (96-100%) because MR imaging incorrectly identified small hemangiomas as possible tumors in four patients. MR imaging was better than CT in identifying metastatic lesions in the liver. For the localization of primary gastrinoma, assessed in 32 patients, MR imaging had a sensitivity of 25%, ultrasound 19%, CT 28%, all three together 38%, and angiography 59%. Localization of metastatic gastrinoma in the liver or primary gastrinomas in 16 patients was assessed before and after gadolinium-DTPA (0.1 mmol/kg). The sensitivity and specificity of MR imaging was unchanged but bolus injection and rapid MR acquisition techniques were not used. These results indicate that recent advances in MR imaging have greatly improved its sensitivity for the detection and assessment of the extent of metastatic gastrinoma. MR imaging is now the imaging study of choice to assess metastatic pancreatic endocrine tumors in the liver. In contrast, the detection of primary tumors by MR imaging has not improved; therefore, angiography remains the study of choice.

Adult↗