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Biomedical subjects

R T Jensen

Publications and source records attributed to R T Jensen.

At least 127 records · Page 7Linked to original sources
PubMed1996

Prolonged hypergastrinemia does not increase the frequency of colonic neoplasia in patients with Zollinger-Ellison syndrome.

Whereas considerable experimental evidence suggests chronic hypergastrinemia can increase the occurrence of colonic neoplasia, the risks in man remain unclear. Zollinger-Ellison syndrome (ZES) is associated with marked plasma elevation of all forms of gastrin and, because of its prolonged course, has been shown to be an excellent model disease to study the effects of chronic hypergastrinemia in man. To determine whether profound chronic hypergastrinemia affects the occurrence of colonic dysplasia and neoplasia, 97 consecutive patients with ZES were studied. All patients underwent colonoscopic examination to the cecum, and the location, size, and type of polyps/tumors were determined. The patients had a mean fasting gastrin level 31 times above normal and a mean disease duration of 10 years; 17/97 (18%) had adenomatous polyps, 67/97 (69%) no adenomatous polyps, and 2/97 (2%) had colonoscopy and/or autopsy studies fo asymptomatic controls. Stratification by age or gender, presence of MEN-I, tumor extent, and duration of degree of hypergastrinemia did not increase prevalence. This study shows that despite prolonged, profound hypergastrinemia, no increased rate of colonic neoplasia (polyps or cancer) was noted. These data suggest that the development of hypergastrinemia secondary to continuous use of H+,K+-ATPase inhibitors for as long as 10 years is unlikely to cause an increased risk of developing colonic neoplasia in man.

Adenocarcinoma↗
PubMed1996

Is reoperation for gastrinoma excision indicated in Zollinger-Ellison syndrome?

BACKGROUND: Surgical excision of gastrinomas in patients with Zollinger-Ellison syndrome (ZES) decreases the incidence of hepatic metastases, but long-term biochemical cures are achieved in fewer than 30% of cases. A growing number of patients have persistent or recurrent disease after initial operation. The effect of reoperation in these patients has not been previously reported. METHODS: From December 1982 to August 1995, 120 patients with ZES underwent operation for gastrinoma resection. Seventy-eight patients had recurrent or persistent ZES after operation; 17 patients underwent 18 reoperations. After initial operation all patients underwent yearly functional and imaging studies. If a tumor was unequivocally imaged, reexploration was done. RESULTS: Five patients, all with sporadic disease, were disease free after operation, with a median follow-up of 28 months. Tumor was found in all 18 reoperations and resected in 17. In patients with continuing disease-free intervals, locations of gastrinomas included pancreatic head lymph nodes (three), liver metastasis (one), and pancreatic tail lymph node (one). There were no deaths in the cured group; two patients in the group with persistent disease have died (median follow-up, 34 months). CONCLUSIONS: Reoperation for gastrinoma excision resulted in elimination of disease in 30% of patients and should be considered for patients with imageable disease.

Adult↗
PubMed1996

Gastrointestinal endocrine tumours. Gastrinoma.

Since the description of the Zollinger-Ellison syndrome in two patients in 1955, there have been significant advances in the understanding of its pathogenesis, natural history, relationship to multiple endocrine neoplasia type 1, diagnosis, methods of tumour localization and management. The main focus in treatment is now shifting from management of the gastric acid hypersecretory state which can now be controlled medically in almost every patient, to the management of the gastrinoma. Recent studies are beginning to provide insights into the natural history of gastrinomas, factors that are associated with invasiveness in some gastrinomas, defining the role of surgery in managing patients with different disease extents, or with MEN 1 and being able to provide insights into molecular abnormalities that may be important in their pathogenesis. In this article each of these advances is briefly reviewed with emphasis primarily on recent advances.

Female↗
PubMed1996

A prospective study of the effectiveness of low dose omeprazole as initial therapy in Zollinger-Ellison syndrome.

BACKGROUND: The proton pump inhibitors (omeprazole and lansoprazole) are the drugs of choice for the medical management of gastric acid hypersecretion in Zollinger-Ellison syndrome (ZES). These drugs are safe for long-term therapy but are acid-labile and high doses are expensive. The recommended starting dose of omeprazole is 60 mg/day. However, it has been shown in recent studies that the maintenance dose of omeprazole could be safely reduced to 20 mg once or twice a day in more than two-thirds of patients with ZES. The purpose of this study is to determine if an initial starting dose of omeprazole 20 mg/day is safe and effective in patients with ZES. METHODS: Forty-nine consecutive patients with ZES being treated with ranitidine for at least 2 weeks were admitted to the NIH. Omeprazole 20 mg was started on day 1 of the admission and ranitidine discontinued 4 h after the first dose. Gastric acid output was measured for 1 h prior to the next omeprazole dose on day 2, then on day 3 if the value was > 10 mmol/h on the previous day. If acid-peptic symptoms developed or the gastric acid output remained > 10 mmol/h on day 3, the patient was considered to have failed omeprazole 20 mg/day initial therapy and the dose titrated daily to achieve adequate control of acid-peptic symptoms and gastric secretion. RESULTS: In 33 of the 49 patients (68%) omeprazole 20 mg/day was successful as initial therapy. Sixteen patients (32%) failed this initial omeprazole dose (eight patients owing to persistent peptic symptoms and eight patients owing to inadequate acid control). The final daily omeprazole dose required in these patients was 40 mg in eight patients (16%), 60 mg in one patient (2%) and 80 mg in seven patients (14%). Basal acid output (BAO) was the only clinical or laboratory feature that was significantly different between the two groups in which low dose initial omeprazole therapy was or was not successful; all patients with basal acid output < 20 mmol/h had a successful outcome. CONCLUSIONS: Because of the need to rapidly control gastric acid hypersecretion owing to the high risk of complications from peptic ulcer disease, patients with ZES should continue to be started on omeprazole 60 mg/day and the dose adjusted by acute titration methods as is currently recommended. After a maintenance dose is established, attempts should be undertaken to reduce the dose to 20 mg/ day once or twice a day. Only the minority of patients with ZES in whom basal acid output is known to be < 20 mmol/h (20% of patients) should be started on a low initial omeprazole dose.

Adult↗
PubMed1996

Metastatic gastrinomas: localization with selective arterial injection of secretin.

PURPOSE: To evaluate localization of hepatic metastases with the intraarterial secretin injection test in Zollinger-Ellison syndrome (ZES). MATERIALS AND METHODS: Results in 74 patients with ZES (aged 15-70 years) were retrospectively studied. All patients had undergone computed tomography (CT), magnetic resonance (MR) imaging, ultrasound, abdominal angiography, and an intraarterial secretin test, in which venous blood is sampled periodically after injection of secretin. RESULTS: Twenty-two patients had liver metastases. An increase in venous gastrin concentration of at least 25% at 20 seconds or 50% at 30 seconds after injection indicated a positive result. Results were positive in 41% of patients with and 2% without liver metastases (P < .0001). Sensitivity of the intraarterial secretin test was 41%; of CT and ultrasound, 64%; and of MR imaging and angiography, 77%. Intraarterial secretin test results assisted in clinical management in 22% of patients. CONCLUSION: With the criteria developed, the intraarterial secretin test had high specificity but low sensitivity. It should be used when imaging results are unclear.

Adolescent↗
PubMed1995

Comparison of the peptide structural requirements for high affinity interaction with bombesin receptors.

Recently it has been established that both a gastrin-releasing peptide (GRP)-preferring bombesin receptor and a neuromedin B-preferring bombesin receptor mediate the mammalian actions of bombesin-related peptides. Because many tissues used for studies of the structure-activity relationship of these peptides possess both receptor subtypes and none possess only the neuromedin B-preferring subtype, there is minimal information on the peptide structural features determining receptor selectivity and it is unknown whether the determinants of agonism at both bombesin receptor subtypes are similar. In the present study we have used native cells either possessing only one bombesin receptor subtype or stably transfected with one subtype to study in detail the peptide structural requirements for interacting and activating each receptor subtype. For the naturally occurring agonists, at the GRP-preferring bombesin receptor the relative affinities were litorin = ranatensin = bombesin > GRP >> neuromedin B, phyllolitorin and at the neuromedin B-preferring bombesin receptor were litorin = neuromedin B = ranatensin > bombesin, phyllolitorin >> GRP. For the GRP-preferring bombesin receptor the heptapeptide and for the neuromedin B-preferring bombesin receptor the octapeptide was the minimal carboxyl fragment interacting with the receptor/or causing biologic activity, and the nonapeptide and full decapeptide, respectively, were the minimal required for full affinity. Making neuromedin B more bombesin- or GRP-like by replacing amino acids in position 3, 6, and 9 demonstrated that position 3 was the most important, followed by position 9 for receptor subtype selectivity. A conformationally restricted GRP analogue, [D-Cys6,D-Ala11,Cys14]bombesin-(6-14) had a significantly higher affinity for GRP-preferring bombesin receptor than NMB receptor. These results demonstrate that: (1) the structure-function relations for the two mammalian bombesin receptors have important differences; (2) suggest that the active conformation of neuromedin B must differ markedly from the beta-sheet model proposed for GRP; and (3) suggest that one important function of the NH2 terminus of GRP and neuromedin B is determining receptor subtype selectivity.

Amino Acid Sequence↗
PubMed1995

Characterization of gastrin-releasing peptide receptor expressed in Sf9 insect cells by baculovirus.

Whereas baculovirus expression systems have been extensively used for high-level expression of steroid receptors and receptors coupled to adenylate cyclase, there are few studies on peptide receptors coupled to phospholipase C (PLC). In the present study we have expressed the murine gastrin-releasing peptide receptor (mGRP-R) in Sf9 cells using a recombinant baculovirus and characterized it structurally and functionally. mGRP-R was detectible 12 h post infection with recombinant baculovirus carrying mGRP-R cDNA and became maximal at 60 h post infection (Bmax = 6 pmol/mg protein), which is a 4-60-fold greater density than is found in native tissues. The mGRP-R in Sf9 cells assessed by affinity labeling or immunoblotting was smaller than that in native tissues (M(r) = 51 kD vs 82 kD), and the difference was due to the extent of glycosylation. In Sf9 cells the mGRP-R had at least two of the four potential extracellular glycosylation sites glycosylated, whereas in the native receptor all four were approximately equally glycosylated. In Sf9 cells the glycosylation was entirely biantennary complex, in contrast to the native mGRP-R, where it was entirely tri- and tetraantennary complex N-linked oligosaccharides. Affinity labeling studies revealed a band with an apparent molecular mass about 40 kDa higher than the 51-kDa mGRP-R band. The intensity of this band correlated with the extent of functional G protein coupling, suggesting that it may represent an mGRP-R-G protein complex. In binding studies the affinity of the mGRP-r in Sf9 cells for the agonists bombesin (Bn), GRP, and neuromedin B (NMB) varied differently with infection time: with Bn the affinity decreased 3-fold with longer infection times, with GRP it remained unchanged, and with NMB it decreased 10-fold. GPP(NH)p inhibited binding of either [125I]Tyr4Bn or [125I]GRP at 24 h post infection, but not at 96 h post infection. Agonists activated PLC, increasing both [3H]IP and [Ca2+]i; however, the efficacy of each agonist decreased with infection time. These results demonstrate that by the use of recombinant baculovirus infected Sf9 cells the PLC-linked receptor mGRP-R can be expressed in amounts significantly greater than those in native tissues. The mGRP-R expressed in these Sf9 cells is incompletely glycosylated and has less complex N-linked oligosaccharide chains, yet it is fully coupled to G proteins and activates phospholipase C, similar to the native receptor, if short infection times are used.(ABSTRACT TRUNCATED AT 400 WORDS)

3T3 Cells↗
PubMed1995

The gastrin-releasing peptide receptor is rapidly phosphorylated by a kinase other than protein kinase C after exposure to agonist.

Several guanine nucleotide-binding protein-coupled receptors are known to be rapidly phosphorylated after agonist exposure. In this study we show that the gastrin-releasing peptide receptor (GRP-R) is rapidly phosphorylated in response to agonist exposure. When [32P]orthophosphate-labeled cells were exposed to bombesin, the receptor was maximally phosphorylated on serine and threonine residues within 1 min. Although addition of 12-O-tetradecanoylphorbol 13-acetate also resulted in phosphorylation of the GRP-R, elimination of protein kinase C activity using the inhibitor 7-hydroxystaurosporine did not prevent bombesin-induced GRP-R phosphorylation. We conclude that a kinase other than protein kinase C is principally responsible for the rapid, agonist-induced phosphorylation of the GRP-R.

Amino Acid Sequence↗
PubMed1995

Chronic desensitization and down-regulation of the gastrin-releasing peptide receptor are mediated by a protein kinase C-dependent mechanism.

The cellular basis of down-regulation and desensitization in phospholipase C-linked receptors is unclear. Recent studies with some receptors suggest that elements in the carboxyl terminus of the receptor are important in mediating these processes. Three mutant gastrin-releasing peptide receptors (GRP-R) were studied: one whose last 37 carboxyl-terminal amino acids were eliminated (construct MGT346); one that replaced all of the carboxyl-terminal Ser and Thr eliminated in MGT346 with Ala, Asn, or Gly (construct JF1); and one that selectively replaced the Ser and Thr of the protein kinase C consensus sequence (PKC-CS) located within the same region with alanine (construct TS360AA). Desensitization was assessed by measuring the ability to activate phospholipase C and increase cellular [3H]inositol phosphates, or increase [Ca2+]i, after pre-exposure to 3 nM bombesin for 24 h. Wild-type GRP-R was maximally desensitized and down-regulated after a 24-h exposure to 3 nM bombesin, and removal of the PKC-CS alone markedly attenuated each process. Elimination of additional serines and threonines by truncation (MGT346) or replacement (JF1) did not decrease down-regulation or desensitization further. To confirm the necessity of second messenger activation in mediating down-regulation, we further investigated two additional mutant GRP-R that bound agonist with high affinity but fail to activate phospholipase C (constructs R139G and A263E). Neither construct underwent significant down-regulation. Removal of all GRP-R carboxyl-terminal Ser or Thr, either by MGT346 or JF1, reduced internalization by > 80%, whereas elimination of the PKC-CS in TS360AA only attenuated internalization by 21 +/- 2%. These data suggest that activation of the distal carboxyl-terminal PKC-CS is essential for chronic desensitization and down-regulation of the GRP-R, and provide no evidence for involvement of second messenger-independent processes. In contrast, internalization is equally regulated by both second messenger-dependent and independent processes.

3T3 Cells↗
PubMed1995

Helicobacter pylori infection. A reversible cause of hypergastrinemia and hyperchlorhydria which may mimic Zollinger-Ellison syndrome.

The present report describes two patients with fasting hypergastrinemia, gastric acid hypersecretion, and Helicobacter pylori gastritis. Provocative testing for Zollinger-Ellison syndrome was negative and imaging studies did not demonstrate an intra-abdominal mass. Following eradication of the Helicobacter pylori infection, the fasting hypergastrinemia resolved in both patients and in one patient the gastric acid hypersecretion also resolved. The implications of this case on the differential diagnosis of Zollinger-Ellison syndrome are discussed.

Adolescent↗
PubMed1995

Bombesin does not stimulate pepsinogen release in isolated gastric chief cells.

Bombesin (BN)-related peptides, such as gastrin-releasing peptide (GRP), have been shown in vivo to stimulate release of pepsinogen. However, whether this is due to a direct interaction with chief cells is not clear. To clarify this we prepared isolated chief cells (> 90% pure) from guinea pig stomach. BN, GRP, or neuromedin B (NMB), at concentrations up to 1 microM, did not stimulate pepsinogen release or affect the stimulation caused by vasoactive intestinal peptide (VIP) (100 nM) or CCK-8 (10 nM), respectively. In addition, BN, GRP, or NMB at a concentration of 1 microM did not increase cAMP nor did they alter the increase in cAMP caused by VIP or secretin. BN (1 microM) did not alter basal cytosolic calcium [Ca2+]i or affect the increase in [Ca2+]i caused by CCK-8 (1 microM). Furthermore, BN, GRP, or NMB at a concentration of 1 microM did not increase the generation of inositol phosphates (IP) or alter the increase in [3H]IP1, [3H]IP2, or [3H]IP3, caused by CCK-8 (1 microM) or carbachol (1 mM). Binding studies demonstrated no saturable binding of either [125I][Tyr4]BN or [125I][D-Tyr0]NMB using experimental conditions where binding with other peptide ligands to other receptors on chief cells is seen. We conclude that BN-related peptides do not interact directly with specific receptors on chief cells to stimulate or alter stimulated pepsinogen secretion, increase the breakdown of inositol phosphates, or alter [Ca2+]i or cAMP.

Analysis of Variance↗
PubMed1995

Inhibitory cyclic analogues and chlorambucil derivatives of bombesin-like peptides.

Analogues of the amphibian neuropeptide, bombesin, and of the mammalian homologue, gastrin-releasing peptide, have been synthesized and their biological activity studied in small cell lung carcinoma and rat pancreatic acinar cells. The compounds are truncated sequences of the active tetradecapeptide BN(1-14) or GRP(20-27). Peptides were cyclized between position 5 or 7 and the carboxyl end of the des-Met14 fragment with D and L Ala11 and Lys5 substitutions, as well as various N-terminal groups attached. The smallest cyclic peptide, BN(7-13), bound to SCLC membranes with microM potency and inhibited BN stimulation of intracellular Ca++ levels. The most potent inhibitor is N-chloroambucil-[His7,D-Ala11]BN(7-13)ethyl ester, which antagonized BN function in SCLC and acinar cells with nM potency and also inhibited clonal growth of carcinoma cell lines.

Amino Acid Sequence↗
PubMed1995

Prospective study of surgical resection of duodenal and pancreatic gastrinomas in multiple endocrine neoplasia type 1.

BACKGROUND: The role of surgical resection of gastrinoma in multiple endocrine neoplasia type 1 (MEN 1) is controversial because of low biochemical cure rates, but with adequate duodenal exploration higher cure rates may be possible. METHODS: We have prospectively evaluated this proposal in ten consecutive patients with MEN 1 and Zollinger-Ellison syndrome who underwent surgical exploration for gastrinoma resection including a detailed evaluation of the duodenum by palpation, intraoperative endoscopy with transillumination, and duodenotomy. RESULTS: Duodenal tumors were present in seven patients. Six of seven patients had metastatic deposits in lymph nodes, and two of seven had synchronous pancreatic tumors. Three patients had a single duodenal tumor, one patient had two tumors, and three patients had more than 20 duodenal tumors. Positive gastrin staining by use of immunohistochemistry was seen in all duodenal tumors. None of these seven patients were biochemically cured. Of three patients with negative duodenal explorations, two had single pancreatic tumors removed and one had only lymph node gastrinoma. No patients were biochemically cured. CONCLUSIONS: Not all patients with MEN 1 and Zollinger-Ellison syndrome have duodenal gastrinomas. In the 70% of patients with duodenal tumors, even extensive duodenal exploration with removal of positive lymph nodes does not result in cures because 86% of tumors had metastasized to lymph nodes and 43% of patients had large numbers of tumors.

Adult↗
PubMed1995

Role of surgery in management of adrenocorticotropic hormone-producing islet cell tumors of the pancreas.

BACKGROUND: Ectopic adrenocorticotropic hormone-producing islet cell tumors of the pancreas (ACTH-ICT) are a rare cause of Cushing's syndrome with a severe and rapidly progressive clinical course. METHODS: Charts were reviewed on all patients evaluated and treated for proven Cushing's syndrome caused by ACTH-ICT (n = 12), specifically for the role of surgery in the management of this disease. RESULTS: Ten (83%) of twelve patients with ACTH-ICT had liver metastases at the time of diagnosis (eight of eight with Zollinger-Ellison syndrome, two of four without Zollinger-Ellison syndrome). Surgical management of the primary tumor included three patients who underwent distal pancreatectomy combined with hepatic resection and one patient who underwent laparoscopic enucleation of a tumor from the pancreatic tail. Eight of twelve patients underwent bilateral adrenalectomy to control symptoms of Cushing's syndrome, including three patients who underwent concurrent distal pancreatectomy and hepatic resection. Six of twelve patients died of the disease within 2 1/2 years of diagnosis, four are alive with progressive hepatic metastases, and one has biochemical evidence of disease. CONCLUSIONS: ACTH-ICT of the pancreas is an aggressive tumor, particularly when there is coproduction of gastrin. The benefit of aggressive surgical resection of primary or metastatic ACTH-ICT has not been established. However, palliative bilateral adrenalectomy is justified, because no patients had biochemical cures after aggressive surgical resection in this series.

ACTH Syndrome, Ectopic↗
PubMed1995

Identification of CCK-A receptors on chief cells with use of a novel, highly selective ligand.

Functional studies suggest that guinea pig chief cells have both cholecystokinin-A (CCK-A) and CCK-B receptors (CCK-A-R and CCK-B-R, respectively). However, all efforts to directly characterize the specific CCK-A-R using binding have been unsuccessful. Recent studies describe specific CCK-A-R agonists such as A-71378 ([desamino-Nle28,31-(N-methyl)Asp32]CCK heptapeptide]. In the present study, [D-Tyr-Gly]A-71378 was synthesized, which has > 300-fold selectivity for CCK-A-R and can be iodinated. [D-Tyr-Gly]A-71378 was equipotent to A-71378 in stimulating pepsinogen release from purified guinea pig chief cells. Binding of 125I-labeled [D-Tyr-Gly]A-71378 was saturable and specific. Potencies for inhibiting binding were as follows: [D-Tyr-Gly]A-71378 = A-71378 = 4x CCK octapeptide (CCK-8) > 1,000x des(SO4)-CCK-8, gastrin. In contrast, for 125I-gastrin binding they were CCK-8 > gastrin-17-I > des(SO4)-CCK-8 >> A-71378 or [D-Tyr-Gly]A-71378. Binding of [D-Tyr-Gly]A-71378 was best fitted by a two-site model. In contrast, 125I-gastrin binding was fitted with a single-site model. For inhibiting binding of 125I-[D-Tyr-Gly]A-71378, the CCK antagonists had relative affinities of L-364,718 >> L-365,260, and the reverse was true with 125I-gastrin. Correlation of binding with changes in biological activity suggested low-affinity CCK-A-R were mediating these changes. These results demonstrate directly for the first time that guinea pig chief cells possess CCK-A-R and CCK-B-R. The pharmacology of these CCK-A-R resembles those on other tissues. This novel, highly selective CCK-A ligand should be useful because it will identify CCK-A-R when they make up as little as 0.2% of the total CCK receptor number.

Animals↗
PubMed1995

Esophageal function and occurrence of Barrett's esophagus in Zollinger-Ellison syndrome.

Manifestations of esophageal disease are present in up to 60% of patients with Zollinger-Ellison syndrome (ZES), although esophageal function has been studied in only a few patients and the prevalence of Barrett's mucosa is unknown in these patients. It is unclear whether the high prevalence of esophageal disease is related to gastric acid hypersecretion alone or to abnormalities of esophageal motility or lower esophageal sphincter (LES) function in addition. To address these issues in the present study esophageal function was evaluated prospectively in 92 consecutive patients with ZES (66 with active disease, 26 disease-free after curative resection) seen during a 1-year period after controlling acid hypersecretion. In the patients with active disease the mean basal acid output (BAO) was 33 +/- 3.0 mEq/h, the maximal acid output (MAO) was 56 +/- 4.0 mEg/h, fasting serum gastrin was 8,736 +/- 4,813 pg/ml and duration of disease prior to study was 12.5 +/- 2.0 years. At the time of manometry, gastric acid secretion was controlled in all patients and no patient had evidence of gastroesophageal reflux disease at upper gastrointestinal endoscopy. Esophageal manometry revealed normal motility in 85% of patients. Eleven percent had low LES pressures, and only 1% of patients had an elevated LES pressure. The frequency of Barrett's mucosa (3%) was similar to that found in the general population but much less than that reported in patients with idiopathic GERD. No correlation was noted between LES pressures or manometric abnormalities and the fasting serum gastrin, BAO, MAO or the presence or absence of multiple endocrine neoplasia type I or previous vagotomy. Esophageal manometric results and LES pressure were similar in disease-free patients and those with active ZES. In conclusion, these results suggest that hypergastrinemia or other disease-specific abnormalities are not contributing to the high incidence of esophageal disease in patients with ZES because esophageal function in patients with ZES is similar to normals. Specifically, motility disorders in patients with ZES occur in similar frequency to normals, and LES pressure is normal in most patients. Despite the high levels of acid secretion and prominence of symptoms, the occurrence of Barrett's mucosa was uncommon (3%) raising the possibility of additional protective mechanisms in patients with ZES.

Adult↗