Biomedical subjects
Publications and source records attributed to A Shulkes.
A congenital diaphragmatic hernia was created surgically in three sheep fetuses in midgestation. After allowing at least one month for interference with lung development, an in-utero repair was performed three weeks before delivery. The study indicates the potential of intrauterine repair for this defect.
The aim of the study was to determine the basal and meal stimulated plasma gastrin and pancreatic polypeptide levels in six morbidly obese patients before and after partial gastric transection (gastroplasty), an operation which results in the distention of the stomach with a small volume of food. The partial gastric transection involved the creation of a proximal gastric pouch of approximately 100 ml, with a 1.2 cm diameter lumen between the proximal and distal gastric pouch. Basal gastrin and pancreatic polypeptide were not altered by the operation. The magnitude of the pancreatic polypeptide response to the mean was significantly depressed, although the time course was not changed. Inhibition of pancreatic secretion is thought to be a physiological function of pancreatic polypeptide, hence its decreased release warrants further investigation in relation to the effect of partial gastric transection on pancreatic function.
The effect of somatostatin infusion on basal plasma gastrin and pancreatic polypeptide (PP) has been examined in the chronically cannulated fetal sheep and in adult sheep. Somatostatin decreased basal gastrin and PP in the fetal sheep. Similar changes were seen in the adult sheep. A rebound of gastrin and PP above control levels occurred when the somatostatin infusion ceased in the adult, but this rebound was not seen in the fetus, probably from the absence of a fetal acid-gastrin feed back loop. The data is compatible with the hypothesis that in the fetus, the low plasma levels of gastrin and PP in mid-gestation are from the inhibition of their secretion by somatostatin.
Hypoacidity and hypergastrinaemia are reported in the newborn human. To investigate the ontogeny of gastrin, plasma gastrin concentrations were measured in chronically cannulated foetal sheep from 100 days gestation to term (145 days) and up to 16 days following delivery. Plasma pancreatic polypeptide (PP) concentrations were measured as a marker of vagal activity. Compared with adult values, foetal plasma gastrin concentration was low at 101-105 days, being 7 +/- 1 pmol/l (mean +/= SEM) but greater than adult values from 130 days gestation and increased to 47 +/- 5 at 141-145 days, and 90 +/- 13 at 1-5 days post-partum. Maternal plasma gastrin level during these periods ranged between 21 and 29 pmol/l and was not related to gestational age. Similarly, maternal plasma PP levels, which varied between 220 and 400 pmol/l, did not correlate with gestational age and did not differ significantly from non-pregnant sheep. Foetal plasma PP was low, 20 +/- at 101-105 days, rose to 92 +/- 17 at 141-145 days, and increased to adult levels in the first week post-partum. Basal foetal and maternal plasma PP were inhibited by iv atropine injection. The increase in plasma PP may represent a maturity of vagal influence. Gastrin and PP have a trophic action on the gastro-intestinal tract, so the observation of significant levels of circulating gastrin and PP in the foetus suggests that they may be involved in maturation of the gastro-intestinal tract.
In the sheep fetus, plasma levels of gastrin are raised above adult levels from 2 weeks before birth. This observation initiated the present study on the maternal and fetal secretion rate, metabolism and placental transfer of gastrin. The experiments were performed on conscious pregnant ewes with chronically cannulated fetuses and on newborn lambs. Metabolic clearance rate (MCR), production rate (PR) and placental transfer of gastrin were measured by alternate steady-state infusion of gastrin into the mother and fetus. Plasma levels of gastrin were measured by radioimmunoassay. Metabolic clearance rate was similar in the pregnant and non-pregnant ewe (8.4 +/- 1.1 (S.E.M.) and 9.0 +/- 1.4 ml/min per kg) respectively. However, fetal MCR was significantly increased. Term was 145 days. Metabolic clearance rate was 15.5 +/- 1.7 at 110-125 days of gestation, 25.6 +/- 2.9 at 126-135 days, 29.7 +/- 4.9 at 136-145 days and remained raised in the first 2 weeks post partum. Gastrin did not cross the placenta in either direction. Placental destruction of gastrin was not responsible for the increased fetal MCR as umbilical artery and umbilical vein levels were not significantly different during fetal gastrin infusion. Furthermore, MCR remained raised in the newborn lambs. Gastrin PR was significantly increased at all ages. The results showed that the previously reported fetal hypergastrinaemia is from fetal sources and is not a result of immaturity of clearance mechanisms. In fact, fetal MCR was significantly increased. The increased fetal plasma gastrin levels are due to an increased rate of production from the fetus.
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Eight male subjects were given pentagastrin by intravenous infusion in doses of 25, 74, 222, 667, and 2000 ng/kg/hr, each dose for 30 min. On another day the same subjects were given the same doses of pentagastrin while gastric inhibitory polypeptide (GIP) was being infused intravenously in a dose of 2 microgram/kg/hr. At the 222 ng/kg/hr dose of pentagastrin, acid output was significantly lower with GIP; at all other doses of pentagastrin, acid output did not differ significantly in tests with and without GIP. Pepsin output in the tests with and without GIP did not differ significantly at any dose of pentagastrin. Plasma concentration of GIP, measured by radioimmunoassay, showed a mean +/- SE plateau level of 7.4 +/- 1.4 ng/ml during GIP infusion and 0.4 +/- 0.1 ng/ml peak level after a standard meal. We conclude that the increase in blood concentration of GIP produced by feeding is probably inadequate to cause significant inhibition of gastric acid or pepsin secretion in man.
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There is now considerable evidence that putative neuropeptides are involved in epileptogenic processes. Neurotensin (NT), which affects neuronal excitability in many parts of the CNS, is potentially relevant to the kindling phenomenon, but has not previously been studied in the kindling model of epilepsy. This study compared the short term (24 hr) and long term (3 wk) effects of amygdaloid kindled seizures, and the short term effects of non-kindled seizures (cortical suprathreshold stimulation-induced seizures, STS), on the concentrations of NT in 13 brain regions in the rat. Whereas kindled seizures produced neither short term nor long term changes in NT, the STS resulted in altered NT concentrations, with a decrease in the cortex and increases in the hippocampus and cervical spinal cord. These results reveal seizure-type specific changes in NT in 3 brain regions; and indicate that although NT does not appear to be involved in kindling, it may be important in the neurochemical mechanisms underlying STS.
The kidney plays a key role in the metabolism of neurotensin (NT). We have examined the renal mechanisms of NT clearance by measuring plasma NT basally and after 45 min infusion of NT(1-13) in intact rats, anephric rats (no glomerular filtration, no peritubular metabolism) and ureteral ligated rats (reduced filtration). Plasma NT was measured by radioimmunoassay with both C (biologically active end) and N terminal directed antisera. In anephric and ureteral ligated rats, basal plasma NT like immunoreactivity measured with either antisera was increased 3-fold compared with unoperated rats. C terminal concentrations were higher than N indicating that a C terminal variant of NT was present in basal plasma. Infusion of NT(1-13) increased N terminal NT from 36 +/- 3 to 249 +/- 35 pmol/l (p less than 0.01) in unoperated rats with significantly larger increases in the renally compromised groups. This was reflected in the reduced metabolic clearance rates (measured with the N terminal directed antisera) in the anephric (16 +/- 1 ml/kg/min) and ureteral ligated (17 +/- 3 ml/kg/min) rats when compared with the control rats (26 +/- 4 ml/kg/min). The similar reductions in the anephric and ureteral ligated rats suggested that the decrease in N terminal NT metabolism was from the absence of filtration. Infusion of NT did not increase C terminal NT immunoreactivity in intact, anephric and ureteral ligated rats showing that the C terminal end was extremely labile. However when endogenous converting enzyme activity was blocked by captopril administration there was a significant increase in C terminal immunoreactivity suggesting a role for converting enzyme like proteases in the clearance of the biologically active end of NT.(ABSTRACT TRUNCATED AT 250 WORDS)
Neurotensin(6-13) has been isolated and sequenced as the major form of neurotensin-like immunoreactivity (NTLI) in a human hepatic fibrolamellar carcinoma. Circulating NTLI in the patient, especially C-terminal, was very high. In additional studies, NT(6-13) was synthesized and compared with the purified tumor NTLI by HPLC analysis and by testing stability in plasma in vitro. These methods confirmed that the tumor NTLI was identical to NT(6-13). Since the metabolic clearance rate of synthetic NT(6-13) in sheep was 30-fold higher than NT(1-13), it suggests that the elevated plasma levels are the result of impaired clearance and/or markedly elevated production.
Gastrin and CCK are believed to have a common ancestor. The gastrin structure has probably evolved from CCK-like peptides at a stage later than the amphibians. To trace the evolution of gastrin and CCK we have determined their structures in an Australian marsupial, the Eastern Grey kangaroo. The brain CCK was identical to CCK-8 of most mammals. The larger form of kangaroo gastrin was a 33mer with the sequence pELHPQDLPHLMTDLSKKKGPWQEEDAAY(SO3)GWMDF-NH2. The 11 italic residues indicate differences from human gastrin. Gastrin-15 and gastrin-16 comprised about 70% of the total immunoreactivity and resulted from cleavage after the second and third residue, respectively, of the unusual tribasic cleavage site. The smaller forms of kangaroo gastrin differ from most other mammalian gastrins in that the N-termini are not blocked with a pyroGlu moiety. Unlike other gastrins, kangaroo gastrin is more than 95% sulfated. The present study indicates that the gastrin structure, as defined by having a Tyr at position 6 from the C-terminus, evolved before the marsupials diverged from the other mammals 130 million years ago.
Progastrin-derived peptides have been reported to stimulate mitogenesis in Swiss 3T3 fibroblasts [P. Singh, A. Owlia, R. Espeijo, B. Dai, Novel gastrin receptors mediate mitogenic effects of gastrin and processing intermediates of gastrin on Swiss 3T3 fibroblasts: Absence of detectable cholecystokinin (CCK)-A and CCK-B receptors. J. Biol. Chem. 270 (1995) 8429-8438]. The aim of the present study was to determine the generality of these findings, by investigating the effect of endogenous and exogenous progastrin-derived peptides on the proliferation of the normal rat kidney fibroblast cell line NRK. Levels of endogenous progastrin-derived peptides were modified by stable transfection of NRK cells with tetracycline-repressible plasmids containing sequences encoding human gastrin in either the sense or antisense orientation. Expression of sense and antisense gastrin mRNA was demonstrated by reverse transcriptase PCR and by radioimmunoassay, and cell proliferation rates were determined by the colorimetric MTT assay. Sense clones produced full length human progastrin, but significant quantities of glycine-extended or amidated gastrin17 were not detected. Concentrations of endogenous rat progastrin in antisense clones were significantly lower than concentrations in clones transfected with vector only. However no difference in proliferation rate was observed between sense, antisense and vector-transfected clones. No stimulation of proliferation was observed in synchronised untransfected NRK cells after supplementation of media with gastrin17 or gastrin17gly in the concentration range 0.3 to 100 nM. Our results do not provide evidence in support of the hypothesis that endogenous or exogenous progastrin-derived peptides act as growth factors in NRK fibroblasts.
Although gastrin is found in adult gastric juice, rapid enzymatic destruction by pepsin in the acid environment makes a physiological role in the adult unlikely. Gastric pH in the fetal sheep is neutral so that gastric juice gastrin could be present, and if present, have a physiological function. The aim of this study was to determine the presence, molecular forms and metabolism of gastrin in gastric juice. Gastrin was present in fetal gastric juice at significantly higher concentrations than in fetal plasma. The majority of gastric juice gastrin was present as the biologically active gastrin-17. Gastrin was stable in normal fetal gastric juice, but was rapidly metabolized to smaller C-terminal fragments when the gastric juice was acidified. With the known growth promoting effect of gastrin on gastrointestinal mucosa, gastrin in fetal juice could have a unique role in the in utero development of the gastrointestinal tract.
1. Calcitonin gene-related peptide (CGRP) is a potent vaso-active 37 amino acid peptide, typically elevated in plasma from patients with medullary thyroid cancer (MTC), but undetectable in the plasma of normal subjects. 2. The kidney is a major site for the clearance of exogenously infused CGRP but the intrarenal site of this clearance is unknown. Extra-organ clearance is also significant for CGRP, and whereas the site and mechanism of this degradation remain uncertain, the vasculature has been postulated as the most likely site. 3. The isolated perfused rat kidney (IPRK) was studied to (i) localize the intrarenal site of CGRP clearance and (ii) determine the contribution of the renal vasculature to the clearance of CGRP. The half-life of CGRP in the filtering IPRK was 63.9 +/- 4.5 min, whereas blocking of filtration by elevation of the perfusate osmolarity abolished the degradation. This suggests that (i) renal CGRP degradation occurs after glomerular filtration with intratubular metabolism and (ii) that there is no active CGRP degradation in the (glomerular) capillary endothelium. 4. These results do not support the theory that renal vascular endothelium plays a major active role in CGRP degradation.
1. Plasma gastrin releasing peptide (GRP) is elevated in the foetal and maternal circulations of pregnant sheep. To determine the mechanisms for this increase the synthesis, secretion rate, metabolism and placental transfer of GRP were measured. 2. Foetal metabolic clearance rate of GRP was significantly increased (P < 0.05) compared to the non-pregnant ewe (19.9 +/- 2.6 (s.e.m.) and 11.8 +/- 2.0 mL/min per kg, respectively). Production rate of GRP in the foetus was four-fold higher than in the non-pregnant ewe reflecting the combination of the increased basal concentration and metabolic clearance rate in the foetus. 3. Infused GRP did not cross the placenta. However, endogenous GRP was higher in the umbilical vein than in the umbilical artery, suggesting a uteroplacental origin for some of the GRP in the foetal circulation. 4. Gastrin releasing peptide mRNA was synthesized in the pregnant endometrium with lower amounts found in the pregnant myometrium. No GRP mRNA was detected in the amnion or chorioallantois. 5. The results show that the previously reported increase in foetal concentration of GRP is from foetal and uteroplacental sources and is not a result of immaturity of clearance mechanisms but rather from an increased production of GRP. With the demonstration that the uteroplacental unit synthesizes and stores GRP, additional studies on the regulation of GRP production from these sources were warranted.
1. The stomach hormone gastrin and the intestinal hormone cholecystokinin (CCK) share a common C-terminal pentapeptide sequence but have different biological roles. Gastrin is the major stimulant of gastric acid secretion and has a growth stimulatory effect on the secretory part of the stomach. The physiological roles of CCK are the stimulation of pancreatic secretion and the contraction of the gall-bladder. 2. Several classes of receptors have been defined for peptides of the gastrin/CCK family. The CCKA receptor on pancreatic acini has a greater affinity for sulfated CCK than for gastrin, while the gastrin/CCKB receptor in gastric mucosa and brain has similar affinities for both gastrin and CCK. Potent and selective antagonists have been developed for both receptor classes. 3. The structures of the CCKA and gastrin/CCKB receptors have been deduced from the nucleotide sequences of cloned cDNA. The receptors, which both belong to the family with seven transmembrane segments, control secretion via similar signalling mechanisms. Occupation of either receptor leads to activation of phospholipase C, with resultant increases in intracellular levels of inositol triphosphate and Ca2+. Mitogenic signalling pathways are also being defined. 4. Recent studies have questioned the previous assumption that gastrin precursors are inactive. Glycine-extended gastrin17 has been shown to stimulate mitogenesis in some cell lines and may also have an autocrine role in the growth of colonic cancers. The receptors involved, which are clearly distinct in binding properties from the CCKA and gastrin/CCKB receptors, have not yet been cloned. Specific antagonists for the novel receptors will be required to define their function in further detail.
Mesenteric ischaemia remains a frequently lethal condition. An improvement in survival is only likely with earlier diagnosis. Even with action upon early diagnosis and re-establishment of circulation, fatal shock often follows. This study was designed to determine the possible role of gastrointestinal regulatory peptides in the haemodynamic pathophysiology of acute mesenteric arterial ischaemia and whether measurement of these peptides would have diagnostic potential. Fourteen anaesthetized sheep were studied, seven with acute superior mesenteric artery (SMA) occlusion and seven with acute superior mesenteric and coeliac artery (SMA + CA) occlusion. Changes in peptide levels and haemodynamic changes were similar in the two experimental groups, but were more pronounced in the more severe ischaemia of SMA + CA occlusion. No major changes in systemic plasma gastrin, pancreatic polypeptide, neurotensin and vasoactive intestinal polypeptide (VIP) occurred during ischaemia. There was, however, a five-fold increase in VIP in portal venous plasma during SMA + CA occlusion. In the reperfusion period there were increases in VIP concentrations in both systemic and portal circulations in both groups. During ischaemia there was a rise in mean arterial pressure and peripheral resistance and a fall in cardiac output. Reperfusion was characterized by systemic and splanchnic vasodilation coincident with the rise in systemic plasma VIP. It is concluded that VIP which is released from the ischaemic intestine is likely to mediate a component of vasodilation seen during reperfusion.