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Biomedical subjects

G J Dockray

Publications and source records attributed to G J Dockray.

At least 91 records · Page 5Linked to original sources
PubMed1991

Immunoneutralization suggests that calcitonin gene related peptide regulates gastric emptying in the rat.

The role of calcitonin gene related peptide (CGRP) in controlling gastric emptying was examined in conscious gastric fistula rats. Rats were immunized with CGRP conjugated to thyroglobulin to produce circulating antibodies for neutralization of the endogenous peptide; control rats received carrier thyroglobulin alone. In the latter acid, protein and hypertonic solutions delayed gastric emptying; in rats with CGRP antibodies the action of acid and hyperosmolal solutions, but not protein, was reversed. The data are compatible with the idea that acid and hyperosmolal solutions release CGRP at the peripheral terminals of visceral afferents in the upper gastrointestinal tract which in turn modifies motility to slow gastric emptying.

Animals↗
PubMed1991

Heterogeneity of chromogranin A-derived peptides in bovine gut, pancreas and adrenal medulla.

Chromogranin A is produced in many endocrine cell types, and is widely used as a marker in endocrine-cell pathology and secretory-cell biology. There is some evidence that it may be proteolytically processed to yield the putative pancreatic regulatory peptide, pancreastatin, and, in order to characterize the relevant pathways in gastrointestinal and pancreatic endocrine cells, we have used, in radioimmunoassay, site-directed antibodies to pancreastatin itself (L331) and to a sequence of chromogranin A immediately C-terminal to pancreastatin (L300). The latter antibody revealed three major forms of immunoreactivity of 8 kDa and five peptides of approx. 3 kDa in bovine pancreas and gut extracts. The 8 kDa peptides were characterized as chromogranin A-(248-313)-peptides, i.e. C-terminally extended forms of pancreastatin; two of the 8 kDa variants differed in two positions, confirming a polymorphism predicted from cDNA sequencing. One of the 3 kDa peptides was characterized as chromogranin A-(297-313)-peptide, i.e. the C-terminal heptadecapeptide of the 8 kDa peptide that would be liberated after cleavage to yield pancreastatin. On the basis of chromatographic studies, immunohistochemistry and the stoichiometry of different immunoreactive peptides, three different pathways of chromogranin A processing were identified: in adrenal chromaffin cells chromogranin A existed mainly as the unmodified intact protein, in pancreatic islet and gastric antral endocrine cells pancreastatin and the 3 kDa peptides were major products, but in small intestine and gastric corpus endocrine cells there was little nor no pancreastatin and the 8 kDa cleavage product predominated. There are therefore important differences in the distribution of chromogranin A-derived peptides between quite closely related populations of endocrine cells that are attributable not only to variable post-translational cleavage but also to the expression of different primary sequences. It seems possible that in different cell types chromogranin A-derived peptides might subserve a variety of different functions.

Adrenal Medulla↗
PubMed1991

The role of calcitonin gene-related peptide in gastric mucosal protection in the rat.

The presence of circulating antibodies to calcitonin gene-related peptide (CGRP) enhanced the damaging effect of ethanol on the rat gastric mucosa. Taken together with previous experimental and morphological data the results suggest that CGRP released from the peripheral terminals of visceral afferent fibres plays a role in mediating gastric mucosal defence mechanisms.

Afferent Pathways↗
PubMed1991

Reversal by omeprazole of the depression of gastrin cell function by fasting in the rat.

1. Gastrin (G)-cell function is controlled by gastric acid, which has inhibitory effects, and food in the gastric lumen, which has stimulatory effects. We have examined the role of acid in mediating the depression of G-cell function that occurs in fasting in the rat. 2. Rats were fasted for 48 h, and received either the H(+)-K(+)-ATPase inhibitor omeprazole, to reduce acid secretion, or vehicle. Basal acid secretion was not significantly different after fasting for 24 or 48 h. Fasted rats which received omeprazole were achlorhydric. 3. In rats treated with vehicle and fasted for 48 h, plasma and tissue gastrin concentrations were significantly depressed. The fall in both parameters suggests an inhibition of gastrin synthesis and consistent with this a decrease was observed in tissue gastrin mRNA abundance and in phosphorylation of progastrin-derived peptides. 4. In fasted rats treated with omeprazole, tissue gastrin concentrations were not significantly different from those of rats fed ad libitum, but plasma gastrin concentrations were significantly higher than in rats fed ad libitum. Gastrin mRNA abundance and the phosphorylation of progastrin-derived peptides in omeprazole-treated rats was not significantly different from rats fed ad libitum. 5. The data suggest that the depression of G-cell function which occurs in fasted rats can be attributed to the inhibitory action of intraluminal acid on the G-cell. Gastric acid appears to regulate several different aspects of G-cell function, including gastrin synthesis, post-translational processing and secretion.

Animals↗
PubMed1991

Efferent pathways in the reflex control of gastric emptying in rats.

Previous studies have established that acid, hypertonic, or protein-rich liquid test meals delay gastric emptying by reflex pathways involving the extrinsic innervation of the gut. To characterize the efferent pathways involved in these reflexes, we have studied the emptying of liquid test meals in control rats and in rats after celiac ganglionectomy, pyloroplasty, and treatment with guanethidine or 6-hydroxydopamine, and in rats with circulating vasoactive intestinal polypeptide (VIP) antibodies. The results suggest that the action of hypertonic solutions on gastric emptying requires an intact celiac ganglion, that acid requires an intact pylorus, and that the action of protein-rich meals is suppressed by VIP antibodies. Sympathetic adrenergic neurons do not apparently mediate the gastric emptying of any of these solutions. The results suggest that there are at least three different reflexes by which the different components of a mixed meal might control gastric emptying. The results are also consistent with the idea that vagovagal reflexes mediate the action of protein-rich solutions on gastric emptying in rats.

Animals↗
PubMed1991

Hormonal control of avian pancreas by gastrin-releasing peptide from the proventriculus.

Endocrine cells in the acid-secreting part of the avian stomach, the proventriculus, contain two forms of gastrin-releasing peptide (GRP) of 27 and 6 residues, respectively. We have examined the actions of exogenous GRP-27 and GRP-6 and endogenously released GRP in the control of pancreatic secretion in urethan-anesthetized turkeys. Chicken GRP-27 and the structurally related amphibian peptide bombesin were potent stimulants of fluid and protein output from the pancreas (at 6-100 pmol/kg, iv). GRP-6 had no significant effect at doses up to 1,000 times higher. A bombesin antagonist, (CH3)2-CHCO-[D-Ala24]GRP-20--26-NHCH3, inhibited the action of exogenous chicken GRP-27 but did not inhibit intravenous cholecystokinin octapeptide (CCK-8). Distension of the proventriculus with a solution of peptone produced an increase in the flow of pancreatic juice and an increase in protein output, which was not reduced by atropine. The bombesin antagonist produced a reversible inhibition of this response. A CCK-gastrin antagonist, BOC-beta-Ala-Trp-Leu-Asp-O(CH2)2- phenyl(4F), which inhibited the action of exogenous CCK, had no effect on the pancreatic response to exogenous GRP-27 or to distension of the proventriculus with peptone. We suggest that protein-rich solutions in the proventriculus release GRP, which in turn acts directly on the pancreas to stimulate enzyme secretion.

Amino Acid Sequence↗
PubMed1991

The secretory kinetics of the G cell in omeprazole-treated rats.

Prolonged achlorhydria leads to hypergastrinemia which must be matched by increased gastrin production. The extent to which the balance between synthesis and storage or secretion is shifted in achlorhydria remains uncertain. In the present study, rats were treated for 14 days with the hydrogen-potassium-stimulated ATPase inhibitor omeprazole, and the effects on plasma and tissue gastrin concentrations and on the abundance of gastrin messenger RNA were examined. To calculate the fractional release rates of gastrin, the metabolic clearance rate of synthetic unsulfated rat heptadeca peptide gastrin in anesthetized rats was also measured. Treatment with omeprazole for 14 days led to a profound hypergastrinemia, a twofold increase in antral gastrin stores, and a tenfold increase in messenger RNA. Calculations based on the metabolic clearance rate for rat heptadecapeptide gastrin suggested that in control rats, about 0.08% of stored gastrin was released per minute compared with about 0.4% in omeprazole-treated rats. No evidence was observed to suggest that changes in the efficiency of conversion of Gly-extended gastrins to amidated peptides were of any significance in accounting for the increased production of amidated gastrin. The increased gastrin synthesis in achlorhydria is therefore attributable to increased messenger RNA levels; most of the increase in gastrin production is directly secreted as changes in the stores of gastrin appear to be of lesser importance.

Animals↗
PubMed1990

Processing of the gastrin precursor. Modulation of phosphorylated, sulfated, and amidated products.

Post-translational processing of the precursor for rat gastrin yields products that include peptides phosphorylated at Ser96, amidated at Phe92, and sulfated at Tyr87 or Tyr103. The phosphorylation site is immediately adjacent to the processing point that gives rise to the biologically active amidated gastrins. We have examined changes in post-translational processing which occur in gastrin cells from rats that are physiologically stimulated (by feeding) or unstimulated (by fasting). Peptides were identified using site-directed radioimmunoassays and chromatographic systems that resolve phosphorylated, amidated, and sulfated progastrin products, including intermediates generated prior to amidation (i.e. C-terminal glycine-extended variants). Assays for Phe92-amidated peptides and for the C-terminal tryptic fragment of progastrin indicated decreases in the total tissue concentrations of immunoreactive peptide with fasting; in contrast, the tissue concentrations of glycine-extended biosynthetic intermediates were similar in fasted and fed rats. Taken together the data suggest a relative failure in amidation mechanisms in unstimulated cells. The endopeptidase cleavage of progastrin was not influenced significantly by fasting. However, the phosphorylation of peptide products containing Ser96 was depressed significantly in fasted rats. The proportions of amidated peptides sulfated at Tyr87 were generally lower than their corresponding glycine-extended biosynthetic precursors, but in both cases the proportion of peptide in the sulfated form was lower than for peptides sulfated at Tyr103. Feeding did not change the sulfation of amidated heptadecapeptide gastrin or its glycine-extended variant. The results suggest that the mechanisms determining phosphorylation and amidation of progastrin-related peptides depend on the patterns of stimulation of gastrin cells. The observation that decreased phosphorylation is associated with a failure to produce active amidated products is consistent with a regulatory function for phosphorylation in gastrin production.

Amides↗
PubMed1990

The effect of ondansetron on gastric emptying in the conscious rat.

The 5-HT3 receptor antagonist ondansetron (GR38032F) enhanced the action of a protein-rich solution in delaying gastric emptying in the conscious gastric fistula rat, but had no effect on the emptying of isotonic or hypertonic saline, acid or FOY-305 which delays emptying by release of cholecystokinin (CCK). The specific CCK-A antagonist (L-364,718) increased gastric emptying of protein-rich meals. L364,718 also increased emptying in the presence of ondansetron. They indicate that protein-rich meals release both CCK and 5-hydroxytryptamine which act in different ways to control gastric motility.

Animals↗
PubMed1990

Isolation, sequence and biosynthetic significance of a novel fragment of gastrin-releasing peptide from chicken proventriculus.

The isolation of bombesin-related peptides in chicken proventriculus was monitored by radioimmunoassay using a C-terminal specific bombesin antibody. Two peptides were identified, one corresponded to the 27-residue, chicken gastrin-releasing peptide (GRP-27) previously identified; the other corresponded to its C-terminal hexapeptide. Chicken GRP-27 stimulated pancreatic and gastric acid secretion in anaesthetized turkeys, but the hexapeptide was inactive. No evidence could be found to suggest that the hexapeptide was an artifact of degradation generated during extraction or isolation. It is proposed that the hexapeptide is produced either by chymotryptic-like cleavage of GRP-27 or by trypsin-like cleavage followed by two cycles of dipeptidylaminopeptidase cleavage. This type of biosynthetic processing may be more common than formerly supposed.

Amino Acid Sequence↗
PubMed1990

Immunization with calcitonin gene-related peptide reduces the inflammatory response to adjuvant arthritis in the rat.

The influence of circulating antibodies to calcitonin gene-related peptide on the inflammatory response was examined in rats with adjuvant-induced arthritis. Rats were immunized with alpha calcitonin gene-related peptide conjugated to thyroglobulin, and circulating antibodies were identified by their capacity to bind radiolabelled rat alpha or human calcitonin gene-related peptide. In unimmunized rats and rats immunized with thyroglobulin alone, the secondary lesions (characterized as paw swelling, nodules on ears and tail, and inflamed nose) produced after adjuvant-induced arthritis were similar. However, at 21 days, when these lesions were maximal, the animals immunized with calcitonin gene-related peptide showed decreased numbers of lesions. An additional marker of disease activity, namely alpha 1 glycoprotein levels in plasma, was also measured. Again, plasma alpha 1 glycoprotein levels were similar in rats that were unimmunized or received thyroglobulin alone, but at 21 days were significantly reduced in animals immunized with calcitonin gene-related peptide. In contrast, the initial foot swelling seen in the first few days after injection of adjuvant was not significantly different in the various groups. The results suggest that antibodies to calcitonin gene-related peptide are able to reduce the severity of the adjuvant arthritis syndrome, and that this peptide contributes to the inflammatory response seen in the later stages of the disease model.

Animals↗
PubMed1990

Gastric emptying in rats: role of afferent neurons and cholecystokinin.

Peptone, acid, and hyperosmolal saline delay gastric emptying in conscious gastric fistula rats. We have now studied the emptying of these solutions in animals pretreated with capsaicin to lesion small diameter primary afferents and in rats with both a gastric and duodenal cannula. In capsaicin-treated rats, hyperosmolal saline did not significantly inhibit gastric emptying, whereas the inhibitory action of acid and peptone was reversed but not abolished. In control rats, the action of peptone was inhibited by the selective cholecystokinin antagonist L364,718, but in capsaicin-treated rats, L364,718 enhanced the action of peptone in delaying gastric emptying. In rats with a duodenal cannula approximately 5 cm from the pylorus, intragastric peptone or hyperosmolal solutions only delayed emptying when the duodenal cannula was closed; in contrast, intragastric acid inhibited gastric emptying when the duodenal cannula was open or closed. The results suggest 1) that all three test meals delay emptying by mechanisms depending at least in part on afferent neurons; 2) peptone delays emptying by at least two mechanisms: one is mediated by cholecystokinin A-type receptors and afferent neurons, and the other requires neither these receptors nor small diameter afferents; and 3) acid, but not peptone or hyperosmolal saline, regulates emptying by an action localized to the stomach or proximal duodenum. The results suggest that there are several different reflex pathways by which liquid test meals act to delay gastric emptying.

Afferent Pathways↗
PubMed1990

Modulation of posttranslational processing of gastrin precursor in dogs.

The precursor of the acid-stimulating hormone gastrin is processed in pyloric antral gastrin cells by steps involving sulfation, phosphorylation, cleavage, and amidation. We describe here changes in posttranslational processing in dogs with a surgically excluded antrum; in the preparation we used there was an intact pylorus but antral mucosa was excluded from the normal influence of the luminal contents. Three to five months after the operation, basal plasma gastrin increased from 30.1 +/- 4.0 to 66.1 +/- 16.1 pmol/l, and concentrations of gastrin in the excluded mucosa were 9.23 +/- 1.75 compared with 3.2 +/- 0.56 nmol/g in control antral mucosa. Calculations based on the metabolic clearance rate and plasma and tissue gastrin concentrations suggest two-fold lower fractional release rates from the excluded G-cells compared with normal G-cells. Radioimmunoassay of tissue extracts using antisera specific for the extreme COOH-terminus of progastrin, for glycine-extended G-17, and for the COOH-terminus of G-17, combined with gel filtration and ion exchange chromatography, indicated normal endopeptidase cleavage of progastrin. However there was significantly reduced phosphorylation of the COOH-terminal tryptic fragment of progastrin, and there was also decreased conversion of Gly-extended intermediates to the biologically active COOH-terminally amidated forms of gastrin. Thus, in spite of hypergastrinaemia, the excluded antral mucosa showed evidence of decreased secretory rates associated with decreased progastrin phosphorylation and amidating enzyme activity. The results suggest that contact of antral mucosa with the luminal contents is able to modulate the posttranslational processing of progastrin and so determine the production of biologically active hormone.

Amino Acid Sequence↗
PubMed1990

Pharmacology of the myogenic heart of the pond snail Lymnaea stagnalis.

1. We have used pharmacologic, immunologic, and biochemical techniques to examine the role of neurochemicals in modulating the myogenic heart of the snail, Lymnaea. 2. 5-HT [high-pressure liquid chromatography (HPLC) and immunocytochemistry], dopamine (HPLC), FMRFamide-related peptides (radioimmunoassay and immunocytochemistry) and substance P-related peptides (immunocytochemistry) were shown to be localized within heart tissue. 3. The pharmacologic actions of these substances on the auricle from an isolated heart preparation were examined together with other putative modulators, acetylcholine (ACh), small cardioactive peptides A and B (SCPA and SCPB), [Arg]8vasotocin (AVT), and Lymnaea native FMRFamide-related peptides [Phe-Met-Arg-Phe-NH2 (FMRFamide), Ser-Asp-Pro-Phe-Leu-Arg-Phe-NH2 (SDPFLRFamide) and Gly-Asp-Pro-Phe-Leu-Arg-Phe-NH2 (GDPFLRFamide)]. 4. The response to each substance could be distinguished by different effect on beat rate, amplitude, and diastolic tonus, as well as by the duration of responses to standard 1-min applications. ACh was inhibitory at low concentrations (threshold less than 10(-10) M) but excitatory at high concentrations (10(-6) M). AVT was alone in producing no dose-dependent response. At high concentrations (10(-4) M), AVT caused a massive tonic contraction and cessation of auricle beat. All other substances examined were excitatory. 5. Antagonists to 5-HT (cinanserin), dopamine (ergonovine), and ACh (alpha-bungarotoxin) were identified. 6. ACh, 5-HT, dopamine, and FMRFamide-related peptides all acted on the auricle at low concentrations, and the rapid onset and short duration of their excitatory effects (ACh inhibitory at low concentrations) suggested that they may have roles as neurotransmitters. SCPA and SCPB were also potent (threshold less than 10(-10) M) but produced long-duration responses suggesting a modulatory or hormonal role.

Animals↗
PubMed1990

Regulation of heartbeat in Lymnaea by motoneurons containing FMRFamide-like peptides.

1. Intracellular stimulation of single neurons in the Lymnaea CNS was carried out to identify heart motoneurons. 2. Two of the identified motoneurons, the E heart excitor (Ehe) cells, were shown to contain Phe-Met-Arg-Phe-NH2 (FMRFamide)-like peptides by immunocytochemical staining of dye-marked neurons and by radioimmunoassay (RIA) applied to extracts of single dissected cells. 3. Bursts of spikes in the Ehe cells increased heart rate, beat amplitude and muscle tonus. This response was mimicked by perfusion of exogenous FMRFamide at low concentration (10(-6) to 5 x 10(-8) M) through the interior of the intact heart. 4. Application of selective antagonists to 5-hydroxytryptamine (5-HT) and dopamine failed to block Ehe cardiac effects. 5. Detailed evidence that the Ehe cells were heart motoneurons was obtained. 1) Anatomic mapping using the dye Lucifer yellow showed Ehe cells had peripheral projections restricted mainly to the intestinal nerve, the only nerve known to innervate the heart. 2) Perfusion of the CNS with a saline containing Co2+ blocked central chemical synapses but did not affect activity of Ehe cells on the heart. 3) Simultaneous intracellular recordings from Ehe cells and auricle muscle fibers showed unitary excitatory junction potentials following with constant latency from spikes in Ehe cells. 6. The present study elucidates the role of FMRFamide in cardioregulation and provides the first evidence that it acts as an excitatory neurotransmitter on the snail heart.

Animals↗
PubMed1989

In vivo studies on the enhancement of cholecystokinin release in the rat striatum by dopamine depletion.

The release of cholecystokinin-8-like (CCK) immunoreactivity from the rat striatum has been studied in vivo using brain microdialysis. A basal efflux of CCK-like immunoreactivity was not detectable in the majority of experiments. Intrastriatal infusion of veratrine (100 micrograms/ml) increased striatal dialysate levels of CCK-like immunoreactivity above detection limits, representing an overflow into the interstitial fluid. High concentrations of potassium caused similar but less consistent effects. Extracellular dopamine depletion using alpha-methyl-p-tyrosine or reserpine also increased the dialysate content of CCK-like immunoreactivity. In contrast, inhibition of peptidases reported to hydrolyse CCK in vitro did not affect either basal or evoked efflux of CCK-like immunoreactivity. These data demonstrate that CCK-like immunoreactivity may be released from neuronal elements within the striatum by depolarizing stimuli in vivo, and suggest that increased overflow of CCK-like immunoreactivity is associated with dopamine depletion.

Animals↗
PubMed1989

Antibodies to calcitonin-gene related peptide reduce inflammation induced by topical mustard oil but not that due to carrageenin in the rat.

The influence of prior immunization to calcitonin gene-related peptide (CGRP) was examined on responses in two models of inflammation plasma: protein extravasation following topical application of mustard oil to the hind paw, and changes in paw volume following subplantar injection of carrageenin. In rats with antibodies to CGRP, there was an approximately 50% decrease compared to the control animals in extravasation, measured by the Evans blue method after topical mustard oil. In contrast, there was no difference in the inflammatory response to carrageenin in control and immunized rats. The results indicate that CGRP, which is probably released from the peripheral endings of cutaneous primary afferents, plays a role in the inflammatory response to mustard oil, but not carrageenin.

Administration, Topical↗