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Biomedical subjects

A Shulkes

Publications and source records attributed to A Shulkes.

At least 37 records · Page 2Linked to original sources
PubMed1999

Concurrent elevation of fundic somatostatin prevents gastrin stimulation by GRP.

Gastrin-releasing peptide (GRP) can stimulate both gastrin and somatostatin (SOM) secretion, but, as gastrin increases SOM and SOM in turn inhibits gastrin, the overall endpoint in terms of gastrin output is variable. To examine the mechanisms involved, we compared the effects of GRP on gastrin secretion in normal sheep and sheep chronically immunized against SOM. In the normal animal, GRP had no effect on either plasma gastrin or SOM. However, in sheep immunized against SOM, GRP stimulated gastrin secretion, suggesting that the concurrent stimulation of SOM prevents the increase in gastrin secretion. To determine the local source of SOM, GRP was then infused into nonimmunized sheep with cannulas draining blood from the fundus and antrum. GRP stimulated fundic SOM output but inhibited antral SOM and gastrin secretion, demonstrating that the fundus was the source of the SOM. Because cholinergic interactions have a major influence on the effects of GRP, a cholinergic stimulus was administered, and we found that the responses were different: SOM output was inhibited in both the antrum and fundus, and antral gastrin secretion was increased. The present study demonstrates two further instances of the differential regulation of SOM from the antrum and fundus. GRP fails to stimulate gastrin because of an increase in fundic SOM, whereas gastrin levels increase following a cholinergic stimulus because of inhibition of both antral and fundic SOM secretion.

Animals↗
PubMed1999

Developmental regulation of gastric somatostatin secretion in the sheep.

Gastric somatostatin (SRIF) regulates gastric acidity by inhibiting gastric acid and gastrin secretion. SRIF secretion is increased by gastric acidity and also directly by regulators of gastric acid secretion such as gastrin. This direct effect has not been described in the developing animal, nor have the roles of intermediaries such as histamine and gastric acidity been defined. The present study aimed to establish the regulatory role of gastrin and histamine during development on SRIF secretion and also to determine whether the effects of gastrin and histamine are independent of gastric pH. Pentagastrin and histamine were infused on separate occasions into fetal sheep, newborn lambs, and 28-day-old lambs. To determine the roles of endogenous histamine and gastric pH, ranitidine (a histamine-2 receptor antagonist) and omeprazole (a H+/K+ ATPase inhibitor) were coinfused with the agonists. Plasma SRIF and gastrin concentrations were measured by RIA. Pentagastrin stimulated SRIF secretion in the fetus after 131 days of gestation (term is 147 days), whereas stimulation by histamine was effective only after birth. The SRIF stimulatory effect of pentagastrin in 28-day-old lambs was abolished by ranitidine, which also reduced this effect in the adult sheep. This inhibitory effect of ranitidine was shown to be a result of blockade of stimulatory H2 receptors, because in the adult blockade of acid secretion with omeprazole failed to attenuate the response of histamine. These results indicate that in the fetus, gastrin receptors, but not histamine receptors, are functionally involved in the stimulation of SRIF secretion. After birth, both gastrin and histamine stimulate SRIF, but the effect of gastrin is mediated at least in part by the release of endogenous histamine. These responses occur independently of changes in gastric acidity, supporting the concept of a direct negative feedback between SRIF and gastrin.

Aging↗
PubMed1999

Molecular cloning, genomic organization and selective expression of bombesin receptor subtype 3 in the sheep hypothalamus and pituitary.

The bombesin receptor subtype 3 (BRS-3) is considered an orphan receptor as it has a low affinity for bombesin-like peptides and no identified natural ligand. We have reported a novel form of gastrin-releasing peptide (GRP) present in high abundance in the pregnant uterus of women and sheep. As BRS-3 was originally cloned from guinea pig uterus, we postulated that the uterine GRP-like peptide may be its natural ligand. We have therefore cloned the gene for the sheep homologue of BRS-3 and determined its distribution. The sheep BRS-3 gene spans 4 kbp and comprises three exons with intron-exon borders at positions similar to those observed for the human and mouse BRS-3 genes. The predicted amino acid sequence of ovine BRS-3 has approximately 85% identity with the human, mouse and guinea pig receptors. Highly conserved amino acids important in mediating receptor G-protein coupling to second messengers and important in ligand binding were found to be conserved in ovine BRS-3. One potentially important deviation was noted: ovine BRS-3 possesses an arginine residue at position 294 instead of a histidine residue as found in all other BRS-3. His(294) was previously identified as important in ligand-receptor interactions while Arg(294) was implicated in high ligand affinity. Thus ovine BRS-3 may have binding characteristics different from those of the human, mouse and guinea pig BRS-3 receptors. In the ewe, BRS-3 mRNA expression was detected in pituitary and hypothalamus but not in tissues of the pregnant uterus (endometrium, myometrium, chorioallantois or amnion). Nor was BRS-3 expression detected in the non-pregnant uterus or in testis. This pattern of BRS-3 expression is similar to that observed in the mouse but different from that observed in the human, rat and guinea pig. We conclude that there is no local interaction between uterine GRP-like peptide and BRS-3. However, the high expression of BRS-3 in the pituitary coupled with elevated circulating levels of this GRP-like peptide during pregnancy suggests an alternate pathway. Cloning of the ovine BRS-3 gene will permit a detailed functional analysis of this receptor in the sheep and its role in the mediation of action of uterine GRP.

Amino Acid Sequence↗
PubMed1998

Expression of progastrin-derived peptides and gastrin receptors in a panel of gastrointestinal carcinoma cell lines.

To assess the potential of gastrin receptor antagonists in the treatment of gastrointestinal cancer, the presence of an autocrine loop involving progastrin-derived peptides has been investigated in two colorectal and one gastric carcinoma cell lines. Progastrin, glycine-extended gastrin and amidated gastrin were detected in cell extracts or conditioned media by radio-immunoassay. Low-affinity binding sites for glycine-extended gastrin and amidated gastrin were present, but high-affinity binding sites were not detected with the appropriate iodinated ligands. In addition, neither glycine-extended gastrin nor amidated gastrin in the concentration range 10pmol/L-10nmol/L stimulated cell proliferation. We conclude that it is unlikely that the carcinoma cell lines LIM 1215, LIM 1839 and LIM 1899 use either amidated or glycine-extended gastrins as extracellular autocrine growth factors.

Cell Line↗
PubMed1998

Regulation of fundic and antral somatostatin secretion by CCK and gastrin.

CCK and gastrin stimulate somatostatin (SOM) secretion and thus modulate their direct effects on the parietal cell. Although SOM is stored in D cells of the fundus and antrum, the nature of the cell type differs, and it is not known whether both regions respond to the stimulatory effects of CCK and gastrin. The objectives of the present study were to determine the separate effects of CCK and gastrin on fundic and antral SOM secretion and to assess the type of receptor involved, using CCK-A (L-364,718) and CCK-B/gastrin (L-365,260) receptor antagonists. Changes in SOM were measured in plasma collected from cannulas draining blood from the fundus (gastric vein) and antrum (gastroepiploic vein) in anesthetized sheep. Both CCK and gastrin significantly stimulated SOM from the fundus and antrum. Sulfated CCK-8 (CCK-8S) increased SOM secretion from the fundus and antrum through interaction with both type A and B receptors. In contrast to CCK-8S, sulfated gastrin-17 (G-17S) stimulated SOM from the fundus via the type B receptor alone, whereas in the antrum G-17S stimulated SOM secretion independent of the A and B receptors. Histamine mediated, at least in part, the SOM-stimulatory effects; an H2-receptor antagonist blocked CCK-stimulated SOM secretion in both the fundus and antrum and reduced gastrin-stimulated SOM secretion in the fundus. The present study demonstrates regionally distinct regulatory mechanisms for gastric SOM secretion by CCK and gastrin.

Anesthesia↗
PubMed1998

Active immunization against somatostatin alters regulation of gastrin in response to gastric acid secretagogues.

We have examined the coupling between somatostatin, gastrin, and gastric acidity, using sheep chronically immunized against somatostatin. All immunized sheep had high-titer (3.2 x 10(5) +/- 1.1 x 10(4) M), high-affinity (1.5 x 10(11) +/- 1.2 x 10(10) l/mol) antibodies. However, basal gastrin and gastric acidity were similar to those in control animals, indicating that an inhibitory somatostatin tone was not required for the maintenance of normal basal gastrin and gastric acidity. Omeprazole (a proton pump inhibitor) increased gastric pH to a similar extent in both the control and immunized groups but resulted in a smaller increase in plasma gastrin in the immunized sheep, thus calling into question the assumption that hypergastrinemia associated with hypochlorhydria is the result of somatostatin withdrawal. Pentagastrin- or histamine-stimulated somatostatin secretion reversed or attenuated the omeprazole-induced hypergastrinemia in control but not immunized sheep, demonstrating a functional role for somatostatin and the biological efficacy of the somatostatin immunization. In a separate series of omeprazole-treated sheep, restoration of an acidic gastric pH with intragastric HCl reversed the hypergastrinemia in both control and immunized animals. We conclude that somatostatin is not essential for the acid-mediated regulation of gastrin. The use of a chronically immunized model as opposed to the acute administration of somatostatin antibodies has important advantages in determining the steady-state regulatory role of somatostatin.

Animals↗
PubMed1998

Temporal expression and cellular localization of a gastrin-releasing peptide-related gene in ovine uterus during the oestrous cycle and pregnancy.

Synthesis of both mRNA and peptide for gastrin-releasing peptide (GRP) has been demonstrated in the pregnant endometrium of sheep and women. However, it is not known whether GRP is synthesized in the sheep uterus during the oestrous cycle. Furthermore the cellular site of GRP mRNA synthesis in the uterus has not been determined. Therefore we examined the synthesis of GRP and determined the cellular location of GRP peptide and mRNA in sheep uterus taken at different times during the oestrous cycle (duration 17 days) and pregnancy (duration 145 days). Northern blot analysis of RNA isolated from ovine endometrium revealed low or no GRP mRNA at days 4, 10, 12 and 14 of the oestrous cycle and a 24-fold rise in GRP mRNA (normalized to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA) between days 14 and 16. A similar pattern was observed during early pregnancy, with a 12-fold rise in GRP mRNA:GAPDH mRNA between days 17 and 20 of pregnancy. Levels of GRP peptide were determined by RIA and found to be low in endometrium isolated at days 4, 10, 12 and 14 of the oestrous cycle (1.0-1.6 pmol/g) and 4 to 5-fold higher at day 16. In situ hybridization localized GRP synthesis to the epithelial cells of the uterine glands at day 16 of the oestrous cycle and at days 17, 20, 40 and 50 of pregnancy. At day 140 of pregnancy diffuse hybridization to cells of the myometrium was also observed. Immunohistochemistry localized GRP peptide to the apical cytoplasm of uterine glandular epithelial cells at day 16 of the oestrous cycle. For samples obtained at day 20 of pregnancy, the area surrounding the glands also showed moderately strong staining. Further staining in the glandular lumen and the stromal tissue surrounding the glands was apparent at day 140 of pregnancy. No GRP immunoreactivity could be detected in the peripheral plasma during the oestrous cycle or the first 20 days of pregnancy. Sizing chromatography of GRP immunoreactivity extracted from endometrial tissue taken at day 10 of the oestrous cycle revealed two peaks that co-eluted with GRP(1-27) and GRP(18-27). However, during luteolysis and oestrus the major peak of GRP immunoreactivity extracted from endometrial tissue was larger than GRP(1-27) and similar to that seen previously in the gravid ovine endometrium. These studies demonstrate that a peptide similar to, but larger than, GRP is a major product of the glandular epithelium of the ovine uterus during the luteal regression phase of the oestrous cycle and post-blastocyst implantation in pregnancy and provide further evidence that GRP-related peptides have important regulatory roles in uterine function.

Animals↗
PubMed1998

Propranolol elimination by right and left fetal liver: studies in the intact isolated perfused fetal sheep liver.

Propranolol extraction in vivo by the left lobe of the fetal sheep liver is greater than that by the right lobe, and this may be due to the fact that oxygenation of the left lobe is greater than that of the right lobe. To explore this hypothesis, we studied the elimination of (R)-(+)-propranolol (PROP) by right and left lobes of the intact isolated perfused fetal sheep liver model, in which there is equal oxygenation of both liver lobes. After isolation of the liver, near-term fetal sheep livers (n = 11) were perfused (2.68 +/- 1.05 ml/g liver/min) in situ via the umbilical vein in a 1-liter recirculating system. PROP was infused (1.2 mg/hr) into the reservoir after an initial bolus dose (2.3 mg). Perfusate samples were taken from the common and right and left hepatic veins every 10 min for determination of PROP concentrations and oxygen consumption over the 180-min experimental period. Mean ductus venosus shunt through the liver was 42 +/- 21% of perfusate flow. Oxygen consumption was not significantly different between the left and right lobes of the liver (0.79 +/- 0.46 and 0.67 +/- 0.44 micromol/g liver/min, respectively, P > .05), nor was there any significant difference between lobes in PROP hepatic extraction at steady state (0.25 +/- 0.20 and 0.25 +/- 0.23, respectively, P > .05). This supports the hypothesis that the difference between lobes in PROP extraction in vivo may be due to the difference in degree of oxygenation of the left and right lobes that is known to be present in vivo.

Animals↗
PubMed1997

Cholecystokinin (CCK) regulates somatostatin secretion through both the CCK-A and CCK-B/gastrin receptors in sheep.

1. Cholecystokinin (CCK) and gastrin both stimulate gastric somatostatin (SOM) secretion in vitro and thus have the potential to modulate their direct effects on the parietal cell. However, the relative potencies and the mechanisms of action of CCK and gastrin on SOM secretion in vivo have not been determined. 2. The objectives of the present study were to compare the in vivo potencies of the sulphated(s) and non-sulphated (ns) forms of gastrin heptadecapeptide (G-17) and CCK octapeptide (CCK-8) on SOM secretion, and to determine the nature of the receptors involved by repeating the studies in the presence of the CCK-A and CCK-B/gastrin receptor antagonists L-364,718 and L-365,260, respectively. All experiments were performed in the chronically cannulated sheep. 3. Dose-response experiments revealed the following potencies for SOM secretion: G-17s = CCK-8s > G-17 ns >> CCK-8ns. However, based on the plasma levels achieved and a higher metabolic clearance rate (MCR) for CCK, CCK-8s was the most potent. 4. Both the CCK-A and CCK-B/gastrin receptor antagonists suppressed CCK-8s-stimulated SOM output. In contrast, G-17s-stimulated SOM output was inhibited by only the CCK-B/gastrin receptor antagonist. 5. Both receptor antagonists increased basal plasma gastrin and CCK levels. 6. The predominant circulating SOM molecular form after both gastrin and CCK stimulation was SOM-14. 7. In conclusion, the sulphated forms of CCK and gastrin are more potent than the non-sulphated forms. Despite sharing a common biologically active carboxy terminus, CCK stimulates SOM secretion by both the CCK-A and CCK-B/gastrin receptors, while gastrin acts via the CCK-B/gastrin receptor alone. These findings explain in part why CCK is a net inhibitor of gastric acid secretion in vivo.

Animals↗
PubMed1997

Cholecystokinin-GABA interactions in rodent cortex: analyses of cholecystokinin effects on K(+)- and L-glutamate-induced release of [3H]GABA from rat cortical slices and cultured mouse cortical neurones.

Neurones of the cerebral cortex immunoreactive for the neuropeptide, cholecystokinin (CCK), also invariably contain GABA. Hence CCK is believed to modulate some aspect of GABAergic synaptic activity. The present study therefore investigated the effects of CCK on basal, K(+)- and L-glutamate-induced release of [3H]GABA from slices of rat neocortex and cultured murine neocortical neurones. Rat neocortical prisms loaded with [3H]GABA (10 nM) were superfused with Krebs-Henseleit buffer and stimulated twice (S1 and S2, 2 min) with K+ (30 mM). Release associated with each stimulus was measured and expressed relative to basal release (R1 and R2). The effects of non-selective and CCKB selective agonists, CCK-8S and CCK-4, respectively, on basal and K(+)-induced release of [3H]GABA were subsequently assessed by alternately including the peptides in S2 and comparing R2/R1 and S2/S1 ratios to control experiments. Contrary to previous findings, CCK-8S (30 nM-1 microM) and CCK-4 (0.3 nM-1 microM) failed to influence basal or K(+)-induced release. In similar experiments, murine cortical neurones superfused with HEPES balanced salt buffer, released exogenous [3H]GABA upon stimulation (1 min) with either K+ (55 mM) or L-glutamate (30 microM). However, CCK-8S, CCK-4 (both 300 nM-1 microM) and the CCKB selective antagonist, L365,260 (1 microM), failed to influence basal, K(+)- or L-glutamate-induced release of [3H]GABA from these neurones when included in S2. These data therefore do not support the postulate that CCK acting via CCKA or CCKB receptors modulates release of GABA under the present experimental conditions. GABA-CCK interactions were not specifically studied because only L-glutamate (30 microM) significantly elevated release of CCK-like immunoreactivity (115% above basal) in murine cortical neurones: basal release of CCK was estimated to be 7 and 11 pM from neurones and slices, respectively. Further studies employing more rigorous stimulation and perhaps examining endogenous GABA release are necessary to fully investigate the co-release of CCK and GABA.

Animals↗
PubMed1997

Glycine-extended gastrin acts as an autocrine growth factor in a nontransformed colon cell line.

BACKGROUND & AIMS: The hypothesis that progastrin-derived peptides act as autocrine growth factors for colorectal carcinomas has generated considerable interest. However, the influence of autocrine gastrins on nontumorigenic colonic cells has not been investigated. This study tested the above hypothesis in the nontumorigenic, conditionally immortalized mouse colon cell line YAMC. METHODS: The effects of expression of antisense or sense gastrin messenger RNA, treatment with antibodies against progastrin-derived peptides, or treatment with gastrin receptor antagonists on YAMC cell proliferation were measured. RESULTS: YAMC clones expressing antisense gastrin messenger RNA had reduced levels of immunoreactive progastrin-derived peptides and a reduced rate of proliferation, relative to vector only-transfected cells. Glycine-extended gastrin17, but not amidated gastrin17, reversed the antisense-induced inhibition of proliferation and stimulated the proliferation of sense- or vector only-transfected cells. YAMC cells bound 125I-glycine-extended gastrin17 (Kd, 0.36 nmol/L, 1810 sites/cell), but not 125I-amidated gastrin17, and binding was unaffected by gastrin receptor antagonists including benzotript. Proliferation of all YAMC clones was partially inhibited either by an antibody selective for glycine-extended gastrin or by preincubation with benzotript, and the inhibitory effects were additive. CONCLUSIONS: YAMC cells use nonamidated progastrin-derived peptides as autocrine growth factors, partly through binding to an extracellular receptor selective for glycine-extended gastrin, and partly through an intracellular mechanism.

Animals↗
PubMed1997

Molecular cloning and sequence of the ovine gastrin gene.

A clone encoding ovine preprogastrin was isolated from a sheep genomic library. The deduced 104 amino acid sequence of ovine preprogastrin was 92% and 68% identical to the sequences of bovine and human preprogastrin, respectively. While the similarity was greatest in the gastrin-17 sequence, and unexpected similarity was also observed in the N-terminus of mature progastrin.

Amino Acid Sequence↗
PubMed1996

The pregnant ovine endometrium constitutively expresses and secretes a highly stable bombesin-like peptide, which shares C-terminal sequence but differs structurally from gastrin-releasing peptide.

Previous studies have shown that a peptide closely related to gastrin releasing peptide (GRP) is expressed by the pregnant ovine endometrium throughout gestation, however its molecular form and the mode of its secretion have not been defined. We have partially purified the endometrial GRP-like peptide and characterised it chromatographically. In contrast to other tissues, the main molecular form of endometrial GRP is larger (6-8 kDa versus 1-3 kDa), and based on the increased hydrophobicity of its circulating form after reduction, contains at least one disulfide bond. Reduction and treatment with chaotropic agents showed that the protein is not a cleavage product of pro-GRP bound to a binding protein. Tryptic cleavage demonstrated that the C-terminus of the peptide is closely related to GRP18-27 suggesting that bioactivity is likely. The partially purified peptide remained intact after incubation in ovine plasma for 16 h indicating that it is extremely stable and consistent with an hormonal role during pregnancy. Quantification of peptide from monolayer cultures of ovine endometrial cells showed that the GRP-like peptide was secreted constitutively. These data show that a stable, GRP-like peptide, distinct from the known processing products of pre-pro-GRP is constitutively expressed by the gravid ovine endometrium. Since endometrial GRP has an intact bioactive C-terminus and is mitogenic for numerous tissues including the uterus, then it is likely to play an important regulatory role in ovine pregnancy.

Amino Acid Sequence↗
PubMed1996

Ontogeny of gastrin and cholecystokinin in the colon and duodenum of sheep.

The different roles of gastrin and cholecystokinin in the fetus compared to the adult may be reflected in different distribution patterns. Re-expression of these fetal patterns is often seen in tumours of the adult. Using region-specific antisera and chromatography, we have determined the ontogeny of amidated gastrin (G-amide), glycine extended gastrin (G-gly), and cholecystokinin (CCK) in various segments of the colon and compared it to the developmental profile in the duodenum. Fetal sheep aged 80-90, 115-125 and 135-144 days (term is 145 days), 7-14 day lamb, and adult sheep were examined. In the colon, higher concentrations of G-amide (2.8 +/- 0.2 pmol/g) and CCK (11.7 +/- 1.6 pmol/g) were measured in the fetus while G-gly (0.7 +/- 0.1 pmol/g) was higher in the adult compared to other age groups. The calculated G-gly/G-amide ratio was 0.4 in the fetus and 1.4 in the adult while the CCK/G-amide ratios were 5 in the fetus and 13 in the adult. The duodenum of the lamb rather than the fetus contained the highest concentrations of G-amide, G-gly and CCK (40.3 +/- 9.7, 2.0 +/- 0.4, 109.0 +/- 14.3 pmol/g, respectively) and at concentrations exceeding that in the colon. The results demonstrate two major developmentally regulated features. Firstly as the colon matures, there is a gradual switch between the expression of the gastrin and CCK genes and secondly, the processing to G-amide is attenuated. These findings suggest that non-amidated gastrin should be examined for a potential role as a growth factor in colorectal carcinogenesis.

Animals↗
PubMed1996

Premedication with cyclosporine and perindopril modifies the ischaemia-reperfusion injury during liver resection in rats.

The aim of the present study was to determine whether pretreatment with cyclosporine (CsA), or perindopril (an angiotensin converting enzyme inhibitor) would modify the ischaemia-reperfusion injury of vascular occlusion during liver resection. Rats were allocated to four groups (n = 20 for each group): (i) sham operated; (ii) liver resection only; (iii) CsA (15 mg/kg); and (iv) perindopril (4 mg/kg during the three days before ischaemia-reperfusion injury with liver resection). The ischaemia was produced by a 30 min continuous occlusion. The model was designed to study liver function tests as the principal parameter. Compared with liver resection only, bilirubin was significantly lower with perindopril on days 8 and 23, but significantly higher with CsA on days 1 and 2. The alanine aminotransferase peak (day 1) was significantly lower with both perindopril and CsA. The prothrombin time was significantly less on days 2 and 4 with perindopril and day 4 with CsA. Liver histological changes were minimal in all groups at 30 min ischaemia, but were significantly less severe in the perindopril group. There was a significant decrease in the weight of the regenerated liver at day 23 with perindopril and a significantly lower drop in weight on day 1 and the rate of gain was significantly greater. Perindopril (4 mg/kg) and CsA (15 mg/kg) significantly alter liver function tests, liver histology and bodyweight following an ischaemia-reperfusion injury associated with liver resection. These findings could limit ischaemia-reperfusion injury for major liver resections in the clinical setting.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1996

Expression of gastrin-releasing peptide (GRP) and GRP receptors in the pregnant human uterus at term.

Synthesis of both gastrin-releasing peptide (GRP) and messenger ribonucleic acid (mRNA) has been demonstrated in pregnant sheep, but studies in women have not been reported. Therefore, we examined the uterus and placenta of pregnant women at term for synthesis of GRP and expression of GRP receptor genes BRS-3 and GRP-R. A transcript of 0.95 kilobases, corresponding to GRP mRNA, was detected in endometrium and myometrium, but not in amnion, chorion, placenta, or nonpregnant endometrium. GRP immunoreactivity (GRP-ir) was detected in half (three of six) of the endometrial (1.23 +/- 0.04 pmol/g) and myometrial (0.73 +/- 0.04 pmol/g) samples and in some, but not all, samples of amnion (one of four subjects; 0.6 pmol/g), chorion (four of five subjects; 0.8 +/- 0.2 pmol/g), placenta (two of six subjects; 0.5 +/- 0.2 pmol/g), and amniotic fluid (four of six subjects; 59 +/- 19 fmol/mL). GRP-ir was present in the maternal circulation (44 +/- 12 fmol/mL) and was higher in plasma obtained from the umbilical artery (152 +/- 14 fmol/mL) and vein (143 +/- 24 fmol/mL). The major peak of GRP-ir in pregnant endometrial tissue was larger than GRP-(1-27), as determined by gel filtration chromatography. Minor peaks were also observed: two larger than the main form and one corresponding to GRP-(18-27). mRNA for GRP receptors GRP-R and BRS-3 was detected by semiquantitative reverse transcription-PCR. For both receptors, mRNA was higher in the pregnant endometrium than in the nonpregnant endometrium but was detected in all of the uteroplacental tissues examined. GRP-R mRNA predominated in the pregnant endometrium, whereas BRS-3 mRNA predominated in the membranes and placenta. In these tissues, PCR for BRS-3 mRNA gave rise to an additional product (approximately 50 bp larger). These studies demonstrated that a peptide larger than, but related to, GRP is synthesized in the pregnant human uterus and is secreted into the maternal and fetal circulations. The detection of mRNA for GRP-R, BRS-3, and possibly a transcript variant of BRS-3 as well as the detection of a peptide larger than, but related to, GRP suggest a novel regulatory unit in the human reproductive tract.

Amniotic Fluid↗
PubMed1996

Gastrin processing and secretion in patients with end-stage renal failure.

Gastrin circulates at higher than normal concentrations in patients with end-stage renal failure (ESRF). However, it remains unclear which forms of gastrin are elevated and whether there is also an alteration in the secretory profile after stimulation. In the present study all processed and partially processed forms of circulating gastrin were measured in plasma before and after meal stimulation in ESRF patients and control subjects. Since Helicobacter pylori (HP) infection affects gastrin secretion, HP status was determined. Fasting gastrin-amide (36 +/- 8 pmol/L), gastrin-Gly (55 +/- 16 pmol/L), and total gastrin (218 +/- 32 pmol/L) measured in ESRF/HP-patients were all significantly greater than those in the control group (10 +/- 1, 15 +/- 3, and 17 +/- 2 pmol/L, respectively; P < 0.01). Plasma gastrin-amide (126 +/- 67 pmol/L) and total gastrin (397 +/- 164 pmol/L) were highest in the ESRF/HP+ patients. The proportion of nonamidated gastrin products was 4-fold higher in ESRF patients than in control subjects, suggesting structure-specific changes in gastrin secretion and metabolism, and this was confirmed by chromatography. The meal-stimulated increments in control/HP- and ESRF/HP-groups were similar. However, the ESRF/HP+ group had a markedly potentiated gastrin response. Fasting plasma somatostatin, an inhibitor of gastrin secretion, was also measured and was significantly lower in the ESRF patients than that in the control group. These studies show that the hypergastrinemia associated with renal failure has been underestimated. This is because only amidated products were measured. The potentiated gastrin meal response in ESRF attributed previously to changes in gastrin metabolism are in part explained by the effect of HP infection. The observed diminished somatostatin response suggests that the increase in circulating gastrin in ESRF is the result of loss of inhibition of secretion as well as decreased metabolism. As both amidated and nonamidated gastrin are now considered to have trophic and secretory effects, these findings may explain the gastrointestinal tract hypertrophy often associated with ESRF.

Adult↗