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R T Jensen

Publications and source records attributed to R T Jensen.

At least 145 records · Page 8Linked to original sources
PubMed1995

Interaction of galanin fragments with galanin receptors on isolated smooth muscle cells from guinea pig stomach: identification of a novel galanin receptor subtype.

From structure-function studies it has been proposed that two subtypes of receptors may mediate galanin's actions in the gastrointestinal tract and other tissues and their effects can be either direct or neurally mediated. We have recently demonstrated that isolated gastric smooth muscle cells possess high-affinity galanin receptors, activation of which increases AMP and causes relaxation. Because this cell system contains no neural elements, contains a single class of galanin receptors and allows binding to be correlated with function, it is a good system to investigate peptide requirements for cell activation. Porcine galanin (p-Gal) and rat galanin (r-Gal) were equipotent to the NH2-terminal fragments r,p-Gal(1-10), r,p-Gal(1-15), r,p-Gal(1-20), p-Gal(2-29) and p-Gal(3-29) at inhibiting binding of 125I-galanin to gastric smooth muscle cells from guinea pig (Kd 5-8 nM). The midmolecule fragment p-Gal(9-25) and the long COOH-terminal fragment r-Gal(9-29) were equipotent and 25-fold less potent than p-Gal. Acetylation of r-Gal(9-29) increased potency to that of p-Gal. The short COOH-terminal fragment, p-Gal(21-29) and r-Gal(21-29), had very low affinity (Kd 3 microM). Each peptide alone (1 microM) caused no effect on cell length, but inhibited carbachol-induced contraction. The inhibition was 81% to 92% for r-Gal or p-Gal, r,p-Gal(1-10), r,p-Gal(1-15), r,p-Gal(1-20), p-Gal(2-29), p-Gal(3-29) and Ac-r-Gal(9-29); 47% for p-Gal(9-25) and r-Gal(9-29); and 16% to 17% for p-Gal(21-29).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Peptide structural requirements for antagonism differ between the two mammalian bombesin receptor subtypes.

Recently it has been established that both a gastrin-releasing peptide (GRP) receptor and a neuromedin B (NMB) receptor mediate the actions of bombesin-related peptides in mammals. Five different classes of peptides that function as GRP receptor antagonists have been identified; however, it is unknown whether similar strategies will yield antagonists for the closely related NMB receptor. In the present study we have used either native cells possessing only one bombesin (Bn) receptor subtype or cells stably transfected with one subtype to determine whether using the strategies that were used successfully for GRP receptors would allow NMB receptor antagonists to be identified. [DPhe12]Bn analogs; des Met14 amides, esters and alkylamides; psi 13-14 Bn pseudopeptides; and D-amino acid-substituted analogs of substance P (SP) or SP(4-11) were all synthesized and each functioned as a GRP receptor antagonist. All of these antagonists had low affinity for the NMB receptor. Application of similar strategies to NMB by formation of [DPhe8]NMB, [psi 9-10]NMB pseudopeptides, des-Met10 NMB amides, alkylamide or esters did not result in any potent NMB receptor antagonists. D-Amino acid SP and SP(4-11) analogs were weakly selective NMB receptor antagonists. No COOH-terminal fragments of NMB or GRP functioned as a GRP or NMB receptor antagonist. These results demonstrate that none of the known strategies used to prepare peptide GRP receptor antagonists are successful at the NMB receptor, suggesting that a different strategy will be needed for this peptide, such as the formation of somatostatin octapeptide or D-amino acid-substituted substance P analogs. These results suggest that even though there is a close homology between GRP and NMB and their receptors, their structure-function relations are markedly different. These results indicate that the development of receptor subtype-specific peptide agonists or peptide antagonists for newly discovered receptor subtypes of gastrointestinal hormones/neurotransmitters may be difficult because the strategies developed for one well-studied subtype may not apply to the other even though it is structurally closely related.

3T3 Cells↗
PubMed1995

Expression and characterization of cloned human bombesin receptors.

Little is known about the pharmacology or cell biology of human bombesin (Bn) receptors, because they are usually present at low levels and both subtypes are frequently present in the same tissues. Human gastrin-releasing peptide (GRP) receptors (huGRP-R) and human neuromedin B (NMB) receptors (huNMB-R) were stably transfected into BALB/3T3 fibroblasts. Both receptor types were glycosylated, with 35% of the huGRP-R and 38% of the huNMB-R representing carbohydrate residues. The extent of glycosylation of the transfected huGRP-R was the same as that seen in the human glioblastoma cell line U-118. Radiolabeled agonist ligands were rapidly internalized, whereas noninternalized ligand readily dissociated in a temperature-dependent fashion. The affinities of various agonists for binding to the huGRP-R were Bn (Ki = 1.4 +/- 0.2 nM) = 4 x GRP = 300 x NMB. In contrast, affinities for the huNMB-R were NMB (Ki = 8.1 +/- 5.2 nM) = 4 x Bn = 600 x GRP. [F5-D-Phe6,D-Ala11]Bn(6-13)methyl ester was the most potent huGRP-R antagonist, whereas D-Nal-Cys-Tyr-D-Trp-Lys-Val-Cys-Nal-NH2 was the most potent huNMB-R antagonist. Agonist binding to either receptor type caused activation of phospholipase C and increased cellular [3H]inositol phosphate levels. GRP was potent at increasing [3H]inositol phosphate generation in cells expressing the huGRP-R (EC50 = 13.6 +/- 1.3 nM), whereas NMB was similarly potent when acting upon cells expressing the huNMB-R (EC50 = 9.3 +/- 1.4 nM). However, neither receptor type, when stimulated with agonist, caused an increase in cAMP levels. These data show that stably transfected huGRP-R exhibit similar pharmacology for agonists and antagonists, are appropriately glycosylated, and function similarly with respect to their ability to alter biological activity, compared with natively expressed receptors. Minimal native huNMB-R data are available for comparison, but in general the huNMB-R is similar to the rat NMB receptor in its pharmacology and cell biology.

3T3 Cells↗
PubMed1994

Glycosylation of bombesin receptors: characterization, effect on binding, and G-protein coupling.

In the present study, we investigated the nature and the importance of glycosylation of two mammalian bombesin receptors, the neuromedin B receptor (NMB-R) and the gastrin-releasing peptide receptor (GRP-R), using chemical cross-linking and enzymatic deglycosylation. [125I]-(D-Tyr0)NMB cross-linked to native NMB-R on rat C-6 glioblastoma cells or rat NMB-R transfected into BALB 3T3 cells revealed a single broad band, M(r) = 63,000, on both cell types that was not altered by DTT. NMB inhibited cross-linking specifically and saturably with an IC50 of 4.8 and 6.1 nM for C-6 and NMB-R transfected cells, respectively, and there was a close correlation between its ability to inhibit binding and its ability to inhibit cross-linking. A single broad band of M(r) = 82,000 was cross-linked with [125I]GRP on mouse GRP-R transfected BALB 3T3 cells. Peptide-N4-(N-acetyl-beta- glucosaminyl)asparagine amidase F (PNGase F) digestion increased the mobility of the original band in C-6, NMB-R, and GRP-R transfected cell membranes. Endoglycosidase H (Endo-H) and endoglycosidase F2 (Endo-F2) digestion had no effect on both transfected cells. Neuraminidase digestion slightly increased the mobility of the original band in NMB-R transfected cell membranes; however, it had no effect on GRP-R transfected cell membranes. Endo-alpha-N-acetylglucosaminidase (O-glycanase) digestion subsequent to neuraminidase treatment showed no additional effect on either receptor. Serial partial deglycosylation of cross-linked NMB-Rs with PNGase F treatment for different incubation periods revealed one band of partially glycosylated receptor (53 kDa) besides the fully glycosylated and fully deglycosylated ones, showing that NMB-R has two oligosaccharide chains. Similarly, three partially deglycosylated species (72, 62, and 52 kDa) are seen with the GRP-R, indicating that the GRP-R has four oligosaccharide chains. Treatment of unlabeled membranes with PNGase F followed by affinity labeling resulted in fully deglycosylated NMB-R or 75% deglycosylated GRP-R. Deglycosylation of the NMB-R did not alter its affinity for NMB or alter G-protein coupling; however, 75% deglycosylation of the GRP-R both decreased its affinity for GRP and altered its ability to couple to G-proteins. The present results demonstrate that NMB-R on native and transfected cells is an N-linked sialoglycoprotein with two triantenary and/or tetraantenary complex oligosaccharide chains. The apparent M(r) of this sialoglycoprotein is 63,000, and this protein does not contain disulfide-linked subunits or O-linked carbohydrates.(ABSTRACT TRUNCATED AT 400 WORDS)

3T3 Cells↗
PubMed1994

Desensitization of neuromedin B receptors (NMB-R) on native and NMB-R-transfected cells involves down-regulation and internalization.

The receptor for neuromedin B (NMB-R), a mammalian bombesin-related peptide, is widely distributed in the central nervous system and gastrointestinal tract. While it is known that this receptor is coupled to phospholipase C, like many other phospholipase C-activating receptors, little is known about regulation of the NMB-R subsequent to agonist stimulation. We studied both native NMB-R on C-6 rat glioblastoma cells and wild type NMB-R cloned from rat esophageal muscle which was stably transfected into Balb/3T3 fibroblasts. Both cell types rapidly increased [3H]inositol phosphates and [Ca2+]i in response to 1 microM NMB, whereas preincubation with 3 nM NMB for 3 h markedly attenuated the ability of 1 microM NMB, but not 1 microM endothelin-1, to alter either cell type's biological activity. Prolonged exposure to 3 nM NMB caused a rapid decrease in the number of NMB-R, with the maximal receptor down-regulation seen at 24 h due to NMB-R internalization. After maximal down-regulation, removal of agonist resulted in a rapid restoration of NMB-R to the cell surface of both cell types. NMB-R recovery at 6 h was blocked by monensin, an inhibitor of receptor recycling, but was not affected by cycloheximide, a protein synthesis inhibitor. Resensitization to agonist paralleled the recovery of NMB-R in both cell types, and resensitization likewise was blocked by monensin. Our data demonstrate that the NMB-R undergoes rapid homologous desensitization consequent to agonist stimulation, which is mediated by receptor down-regulation and which, in turn, is regulated by internalization. During resensitization, NMB-R reappearance on the cell surface membrane is independent of protein synthesis and is due to a recycling from an intracellular site.

3T3 Cells↗
PubMed1994

Effect of inhibition of microsomal Ca(2+)-ATPase on cytoplasmic calcium and enzyme secretion in pancreatic acini.

We used thapsigargin (TG), 2,5-di-tert-butyl-1,4-benzohydroquinone (BHQ) and cyclopiazonic acid (CPA), each of which inhibits microsomal Ca(2+)-ATPase, to evaluate the effects of this inhibition on cytoplasmic free calcium ([Ca2+]i) and secretagogue-stimulated enzyme secretion in rat pancreatic acini. Using single-cell microspectrofluorimetry of fura-2-loaded acini we found that all three agents caused a sustained increase in [Ca2+]i by mobilizing calcium from inositol-(1,4,5)-trisphosphate-sensitive intracellular calcium stores and by promoting influx of extracellular calcium. Concentrations of all three agents that increased [Ca2+]i potentiated the stimulation of enzyme secretion caused by secretagogues that activate adenylate cyclase but inhibited the stimulation of enzyme secretion caused by secretagogues that activate phospholipase C. With BHQ, potentiation of adenylate cyclase-mediated enzyme secretion occurred immediately whereas inhibition of phospholipase C-mediated enzyme secretion occurred only after several min of incubation. In addition, the effects of BHQ and CPA on both [Ca2+]i and secretagogue-stimulated enzyme secretion were reversed completely by washing whereas the actions of TG could not be reversed by washing. Concentrations of BHQ in excess of those that caused maximal changes in [Ca2+]i inhibited all modes of stimulated enzyme secretion by a mechanism that was apparently unrelated to changes in [Ca2+]i. Finally, in contrast to the findings with TG and BHQ, CPA inhibited bombesin-stimulated enzyme secretion over a range of concentrations that was at least 10-fold lower than the range of concentrations over which CPA potentiated VIP-stimulated enzyme secretion.

Amylases↗
PubMed1994

Idiopathic gastric acid hypersecretion. Comparison with Zollinger-Ellison syndrome.

Many patients with acid-peptic disease have idiopathic gastric acid hypersecretion defined as a basal acid output > 10.0 meq/hr; however, a significant proportion have basal acid outputs > 15.0 meq/hr, which is within the range found in Zollinger-Ellison syndrome. Although idiopathic gastric acid hypersecretion is more common than Zollinger-Ellison syndrome, it is important that these two disorders be differentiated because of differences in treatment and natural history. In the present study, we compared 124 patients with idiopathic gastric acid hypersecretion and 137 patients with Zollinger-Ellison syndrome. There were no significant differences with regard to age at diagnosis, history of upper gastrointestinal hemorrhage, nausea, vomiting, and family history of duodenal ulcer and other acid-peptic disease. However, significant differences were observed between patients with idiopathic gastric acid hypersecretion and patients with Zollinger-Ellison syndrome with regard to percentage of males: 77% compared to 64% (P = 0.008), mean serum gastrin: 60 pg/ml compared to 3679 pg/ml (normal < 100 pg/ml) (P < 0.001), mean basal acid output: 15.4 meq/hr compared to 47.0 meq/hr (P < 0.001), mean age at onset of symptoms: 33 years compared to 41 years (P < 0.001), mean duration of symptoms before diagnosis: 11 years compared to five years (P < 0.001), percentage with abdominal pain: 67% compared to 82% (P = 0.00004), percentage with diarrhea: 12% compared to 75% (P < 0.000001), percentage with pyrosis: 58% compared to 40% (P = 0.003), percentage with duodenal ulcer: 53% compared to 74% (P < 0.000001), and percentage with esophagitis: 31% compared to 42% (P = 0.0004).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1994

Zollinger-Ellison syndrome can be the initial endocrine manifestation in patients with multiple endocrine neoplasia-type I.

PURPOSE: To determine whether patients with multiple endocrine neoplasia type I (MEN-I) can initially present with Zollinger-Ellison syndrome (ZES), and to learn whether ZES exhibits any distinguishing features when it occurs as a first manifestation of MEN-I. PATIENTS AND METHODS: Sixty patients who had been referred to a clinical research center with ZES were examined by cohort analysis. Twenty-eight had MEN-I and 32 did not. In patients with MEN-I, we analyzed the temporal relationships between the clinical and biochemical manifestations of ZES and the other endocrinopathies associated with the neoplasia. To determine whether patients who had ZES as a first manifestation of MEN-I (n = 8) had any distinguishing clinical characteristics, we compared them to a cohort of patients with established sporadic ZES (n = 32) matched for age, sex, and time since the onset of symptoms consistent with ZES. RESULTS: Of the 28 patients with ZES and MEN-I, 11 initially presented with ZES and hyperparathyroidism (HP) and 1 with evidence only for pituitary disease. Eight patients (29%) presented with features of ZES and developed clinical and biochemical evidence for HP later, while the same number developed these 2 endocrinopathies in the opposite order. In whichever order ZES and HP occurred, the time from the diagnosis of the first to the diagnosis of the second was similar. It ranged from 9 to 177 months in patients who presented with ZES first, and from 12 to 264 months in patients who presented with HP first. At the time of initial diagnosis, the patients who presented with ZES as a manifestation of MEN-I had no distinguishing ZES-related symptoms, biochemical assays, or tumor imaging results compared to the cohort of patients who had the syndrome sporadically. CONCLUSION: Patients with MEN-I can initially present with a symptomatic pancreatic endocrine tumor syndrome without any other disease manifestations. In patients with ZES and MEN-I, up to one third may present with ZES without evidence of any other endocrinopathy. Consequently, patients with presumed sporadic ZES should undergo continual biochemical screening for other endocrinopathies characteristic of MEN-I and, in the future, genetic studies for the MEN-I gene.

Adult↗
PubMed1994

Stimulation of in vivo pancreatic growth in the rat is mediated specifically by way of cholecystokinin-A receptors.

BACKGROUND/AIMS: Cholecystokinin (CCK) and gastrin stimulate growth of rodent pancreas in vivo. However, it remains unclear whether these growth effects are mediated specifically by CCK-A receptors, CCK-B receptors, or both. To clarify this issue, the present study examined the effect of highly selective and biologically active CCK agonists on pancreatic growth. METHODS: Rats were subcutaneously injected with either (1) CCK-8, a nonselective CCK agonist (2.50 micrograms/kg body wt); (2) A-71623, a selective CCK-A agonist, tert-butyl-oxycarbonyl-Trp-Lys (epsilon-N-2-methylphenylaminocarbonyl)-Asp-(N-methyl)-Phe-NH2 (1.84 micrograms/kg body wt); (3) SNF-8815; a selective CCK-B agonist, [(2R,3S)-beta-MePhe28, N-MeNle31]CCK26-33 (2.40 micrograms/kg body wt); or (4) saline (control) for 21 days. Rats were killed, and pancreatic weight, protein content, RNA content, DNA content, protein-DNA ratio, RNA-DNA ratio, pancreatic area per nucleus, and number of mitoses per 10,000 acinar cells were determined. RESULTS: Nonselective CCK agonist significantly increased pancreatic weight, protein, RNA, and DNA contents, and number of mitoses per 10,000 acinar cells. Likewise, selective CCK-A agonist significantly increased pancreatic weight, protein, RNA, and DNA contents, protein-DNA ratio, RNA-DNA ratio, pancreatic area per nucleus, and number of mitoses per 10,000 acinar cells. In contrast, selective and biologically active CCK-B agonist had no effect. CONCLUSION: These findings indicate that pancreatic growth is mediated specifically by CCK-A receptors in the rat in vivo.

Animals↗
PubMed1994

Characterization of somatostatin receptor subtypes controlling rat gastric acid and pancreatic amylase release.

An examination of the binding characteristics of a large number of somatostatin analogues with respect to the five known somatostatin receptor subtypes has recently resulted in the discovery of several peptides with some selectivity for types 2, 3, and 4 and little affinity for type 1 or 5 receptor. A panel of these peptides has thus far implicated type 2 receptors in the inhibition of release of pituitary growth hormone and type 4 receptors in inhibiting pancreatic insulin release. In the present article, we have examined the inhibitory effects of the same group of peptides on in vivo rat gastric acid and pancreatic amylase release and binding to rat pancreatic acinar cells. The type 2-selective ligand NC-8-12 was a potent inhibitor of gastric acid release (EC50s in the 1.5 nM region) whereas the type 4-selective ligand, DC-23-99, elicited little response. However, some involvement of type 3 receptors could not be ruled out because the type 3-selective analogue, DC-25-20, exhibited inhibitory effects at higher dose levels (EC50 > 10 nM). Conversely, the type 4 analogue was a potent inhibitor of amylase release (EC50 1.1 nM) whereas the type 3 analogue had no significant effects at doses tested. DC-23-99 also bound with high affinity to rat acinar cells (EC50 3.8 nM), whereas DC-25-20 exhibited more than 10-fold less affinity. Thus, these two major biological functions of somatostatin appear to be controlled by different receptors and, furthermore, effects on both endocrine and exocrine pancreas appear to be type 4 receptor mediated.

Amino Acid Sequence↗
PubMed1994

Galanin-induced relaxation in gastric smooth muscle cells is mediated by cyclic AMP.

Galanin has numerous effects on gastrointestinal motility in different species; however, its cellular basis of action in mediating these effects is unclear. Dispersed gastric smooth muscle cells have been shown to possess high-affinity galanin receptors that increase cAMP and cause relaxation. Recent studies show some smooth muscle relaxants such as VIP cause relaxation by both cAMP-dependent and -independent mechanisms. It is unknown if galanin's cellular basis of relaxation is similar or different from that of VIP. To investigate galanin's relaxant effect and compare it to VIP's effect, dispersed smooth muscle cells from guinea pig stomach were prepared by collagenase digestion. The mean length in resting cells was 110 +/- 2 microns and, with carbachol treatment, contracted to 89 +/- 2 microns. VIP and galanin alone had no effect on cell length, but each caused a dose-dependent inhibition of carbachol-induced contraction and both had an EC50 of 3-7 nM. Galanin (1 microM) and VIP (1 microM) increased cellular cAMP from 118 +/- 10 pmol/10(6) cells in control to 212 +/- 14 and 214 +/- 12 pmol/10(6) cells, respectively. The protein kinase A inhibitor, Rp-cAMPS, at 100 microM, completely inhibited the relaxant effect of an EC50 concentration of galanin (3 nM), but only inhibited that by VIP by 80% (p < 0.05). Adding the nitric oxide inhibitor, L-NNA (NG-nitro-L-arginine), at 100 microM did not alter the length of resting cells or inhibit carbachol-induced contraction. However, L-NNA (100 microM) decreased VIP-induced relaxation by 45%, whereas it had no effect on galanin-induced relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

A chimeric VIP-PACAP analogue but not VIP pseudopeptides function as VIP receptor antagonists.

The ability to assess the importance of VIP in different physiological processes is limited by the lack of specific potent antagonists. In the present study, we have adopted two different approaches used successfully with other peptides in an attempt to identify new VIP receptor antagonists. One involves the formation of pseudopeptides by insertion of reduced peptide bonds in the NH2-terminus from position 2 to 8 of VIP. The other methodology involves the formation of a COOH-terminal chimeric analogue by combining VIP(6-28) and PACAP(28-38). The ability of each of these peptides to function as an antagonist was compared with reported VIP antagonists. All of the peptides inhibited [125I]VIP binding to VIP receptors on guinea pig pancreatic acini. For the pseudopeptides the affinities were: [psi 3-4]VIP (0.2 microM) = 4 x [psi 4-5]VIP = 8 x [psi 8-9]VIP = 14 x [psi 6-7]VIP, [psi 2-3]VIP = 25 x [psi 5-6]VIP. Each nonpseudopeptide analogue also inhibited VIP binding with relative potencies of VIP(6-28)-PACAP(28-38) (1 microM) = 2.5 x [4-Cl-D-Phe6,Leu17]VIP, VIP(10-28), neurotensin(6-11)-VIP(7-28) = 6 x [Ac-Tyr1,D-Phe2]GRF. All pseudopeptides were agonists with relative potencies: [psi 3-4]VIP > [psi 6-7], [psi 4-5]VIP > [psi 5-6] > [psi 8- 9]VIP > [psi 2-3]VIP. The reported VIP receptor antagonist, neurotensin(6-11)-VIP(7-28), was also an agonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Surgery in Zollinger-Ellison syndrome alters the natural history of gastrinoma.

OBJECTIVE: The authors assessed the impact of gastrinoma resection on the subsequent development of hepatic metastases in Zollinger-Ellison syndrome. SUMMARY BACKGROUND DATA: The symptoms of acid hypersecretion can be controlled medically in Zollinger-Ellison syndrome with high-dose pharmacologic therapy. The current role of surgery is curative excision of the gastrinoma. Because biochemical cure is obtained only in a portion of the patients and the neoplastic disease may be indolent in this syndrome, the ability of surgical resection of gastrinoma to alter or improve the subsequent development of hepatic metastases and mortality has not been defined. METHODS: One hundred twenty-four patients with the biochemical diagnosis of Zollinger-Ellison syndrome and no hepatic metastases on initial imaging studies were evaluated. Ninety-eight patients underwent surgical exploration for curative gastrinoma resections while 26 patients were managed medically. Long-term follow-up regarding development of hepatic metastases and survival were evaluated. RESULTS: Surgical exploration with gastrinoma excision resulted in a significantly decreased incidence of hepatic metastases 3% (3/98) compared with patients managed medically 23% (6/26) with comparable follow-up (p < 0.003). Two deaths due to metastatic gastrinoma occurred in the nonoperative group compared with no disease-specific deaths in the surgical group (p = 0.085). CONCLUSIONS: For the patient with Zollinger-Ellison syndrome without metastatic disease, surgical exploration with attempted curative gastrinoma resection is recommended because it may alter the natural history of this syndrome.

Adult↗