Biomedical subjects
Publications and source records attributed to N D Christofides.
Circular muscle strips of guinea-pig isolated colon relaxed with vasoactive intestinal peptide or peptide histidine methionine, whereas the longitudinal muscle contracted. The non-adrenergic-non-cholinergic inhibitory nerves may therefore be different in these two muscle layers.
Peptide histidine isoleucine (PHI) is a newly discovered peptide from porcine intestine, which has sequence homologies with VIP, an established intestinal secretagogue. To study the effects of PHI in human jejunum, natural porcine PHI was infused intravenously at 10.7 +/- 1.7 pmol/kg/min (mean +/- SEM) in normal volunteers during steady state perfusion of the jejunum with an isotonic bicarbonate-electrolyte solution. Plasma PHI concentrations rose to 279 +/- 26 pmol/l (mean +/- SEM) in the first 20 minutes of the infusion reaching 417 +/- 45 at 40 minutes. At these concentrations PHI induced a net secretion of chloride and sodium and either decreased net absorption or increased net secretion of fluid and potassium, while bicarbonate transport remained unaffected. Peptide histidine isoleucine is a potent jejunal secretagogue in man.
Peptide histidine isoleucine, a 27 amino acid peptide with close amino acid sequence homology to vasoactive intestinal peptide and secretin, is distributed throughout the mammalian intestinal tract, where it has been localised to intramural neurones. An intestinal perfusion technique has been used to study the effect of intravenous peptide histidine isoleucine (44.5 pmol/kg/min) on water and electrolyte transport from a plasma like electrolyte solution in human jejunum in vivo. Peptide histidine isoleucine infusion produced peak plasma peptide histidine isoleucine concentrations in the range 2000-3000 pmol/l, flushing, tachycardia and a reduction in diastolic blood pressure. Peptide histidine isoleucine caused a significant inhibition of net absorption of water, sodium, potassium and bicarbonate and induced a net secretion of chloride, these changes being completely reversed during the post-peptide histidine isoleucine period. These findings suggest that endogenous peptide histidine isoleucine may participate in the neurohumoral regulation of water and electrolyte transport in the human jejunum.
Peptide histidine isoleucine-like immunoreactivity (PHI-LI) was measured by radioimmunoassay in various mammalian ileal extracts fractionated by gel filtration and high-performance liquid chromatography (HPLC). The PHI-LI in the cat, human, guinea-pig and rat tissues were of similar molecular size, being indistinguishable from the porcine standard by gel filtration on Sephadex G-50 superfine, but significant differences were noted on HPLC. The major PHI-LI peaks of guinea-pig and rat were less retained than cat and human PHI-LI which had a similar retention time to porcine PHI. Human PHI-LI, although being chromatographically similar to porcine PHI, was immunologically different. This variation in molecular properties of PHI-LI suggests that extrapolation of experimental results of different species should be treated with great caution.
Peptide histidine isoleucine (PHI), a newly discovered neuropeptide, has been detected by RIA and immunocytochemistry in the upper respiratory tracts of the guinea pig, rat, and cat. HPLC of tracheal extracts showed a single peak of PHI immunoreactivity in each species. The immunoreactive PHI peak found in the guinea pig and rat trachea was eluted earlier than the corresponding peak from the cat, which was coeluted with the porcine PHI standard. Immunocytochemistry showed PHI immunoreactivity to be present within ganglion cells and nerve fibers in the respiratory tracts of all three species. The distribution of PHI was similar to that of vasoactive intestinal polypeptide and ganglion cells were found to contain both PHI and vasoactive intestinal polypeptide immunoreactivities. Pure natural porcine PHI induced a dose-dependent relaxation of isolated guinea pig tracheal muscle which was not blocked by antagonists to catecholamines, histamine, 5-hydroxy-tryptamine, and acetylcholine. PHI may thus be one of the local factors in respiratory control.
A recently developed RIA for human pancreatic tumor GH-releasing hormone (hpGRH1-44NH2) was used to investigate its distribution in the human gastrointestinal tract and brain, and to determine the incidence of its production by tumors. GRH-immunoreactivity (GRH-IR) was present in several regions of the human brain, the highest concentration occurring in the hypothalamus, septum, and substantia inominata. In the gastrointestinal tract GRH-IR was present in the upper intestine, where it was confined to the epithelial mucosa. Approximately one third of all tumors examined (35 out of 97) contained significant amounts of GRH-IR. Gel chromatography of brain and intestinal extracts, and of several tumors, revealed the presence of two molecular forms of GRH-IR, one coeluting with the synthetic hpGRH1-44 amide standard (and also hpGRH1-40) and another eluting significantly later. The earlier eluting GRH-IR peak was found to be similar to the synthetic hpGRH1-44 NH2 and hpGRH1-40 on high pressure liquid chromatography analysis.
To test the discriminatory potential of certain indices of pancreatic function we performed duodenal perfusion studies and measured trypsin, bicarbonate, and lactoferrin outputs, and plasma concentrations of pancreatic polypeptide and motilin in the basal state and during continuous intravenous stimulation with 100 ng kg-1h-1 Ceruletide and 1 CU kg-1h-1 secretin. The following groups were studied: 12 normal volunteers (NV), seven patients with chronic pancreatitis with steatorrhea (CPS), and seven without steatorrhea (CP). Stimulated trypsin outputs, after 45 min of stimulation, were the best discriminant among the groups (NV versus CPS, p less than 0.0005; NV versus CP, p less than 0.005; CP versus CPS, p less than 0.05). Basal trypsin outputs showed similar patterns but failed to discriminate between NV and CP. Bicarbonate outputs were less discriminatory than trypsin outputs. Lactoferrin outputs failed to discriminate, but transient high peak outputs occurred in the initial stimulation period in all four patients with calcific chronic pancreatitis, suggesting a washout phenomenon. Basal motilin levels were elevated in both groups of pancreatitis (p less than 0.05). Stimulated pancreatic polypeptide levels were lower in CPS (NV versus CPS, p less than 0.05) but higher in CP (NV versus CP, p less than 0.005). These differences were also apparent in the basal state. We conclude that the best discrimination among the three groups was achieved by measurement of trypsin outputs, after 45 min of stimulation. In addition, the pancreatic polypeptide response may be used as a marker of residual pancreatic function in chronic pancreatitis.
Plasma immunoreactive peptide histidine isoleucine (PHI) and vasoactive intestinal polypeptide (VIP) levels were measured by specific radioimmunoassays in urethane-anesthetized rats. Basal levels of plasma PHI-like immunoreactivity (PHI-LI) in the hypophysial portal blood were 414 +/- 180 pmol/l (means +/- S.E.), about 7 times higher than in the peripheral blood. VIP-like immunoreactivity (VIP-LI) was also high in the portal blood (399 +/- 139 pmol/l). The correlation coefficient between PHI-LI and VIP-LI was 0.76. These findings suggest that PHI and VIP are co-released from the median eminence into the hypophysial portal blood in rats.
Peptide histidine isoleucine (PHI), first isolated from pig intestine, is distributed identically to vasoactive intestinal peptide (VIP) in all mammals. 42 patients with high plasma VIP secondary to VIPoma also had very high plasma PHI-like immunoreactivity, in a constant ratio to VIP. None of 125 patients with other endocrine tumours had high levels of either peptide. VIPoma tissue from 20 patients also contained PHI shown by immunocytochemistry to be produced by the same cell as VIP. Messenger RNA(mRNA) from one of these tumours contained the codes for VIP and a separate PHI-like sequence. Human PHI-like sequence differed from porcine PHI in only two aminoacid residues. A single cell thus produces two separate regulatory peptides with apparently similar potencies but different spectra of activity. In normal tissue the constant coproduction of two active neuropeptides by a single neuron provides further evidence against the doctrine of one neuron producing only one neurotransmitter.
PHI, infused in man, achieved plateau plasma levels of 297 pmoles/1. The plasma half life was 3.1 min, metabolic clearance rate was 16.4 ml/kg/min and estimated volume of distribution was 73.2 ml/kg. No subjective side effects were noted during the infusion and there was no significant alteration in submaximal pentagastrin stimulated gastric acid or pepsin secretion.
The regional distribution of immunoreactive PHI (IR-PHI) was investigated in rat brain between postcoitum (pc) and day 60 postpartum (pp). IR-PHI was undetectable in all regions of the foetal brain, and only very small amounts were found at day 7 pp. However, there was a dramatic increase thereafter reaching a peak at day 20 pp (e.g. in the hippocampus there was a 12-fold increase in the PHI concentration). Highest concentrations were found in the cortex (40 +/- 5 pmol/g) and hippocampus (35 +/- 8 pmol/g), with lower concentrations in the diencephalon (11 +/- 4 pmol/g) and mesencephalon (10 +/- 3 pmol/g). The brainstem and cerebellum contained very low amounts of IR-PHI. Permeation analysis of brain extracts, on Sephadex G50-superfine, indicated the presence of one major form of IR-PHI which eluted in a similar position to pure intestinal porcine PHI and human intestinal PHI.
Peptide histidine isoleucine-like immunoreactivity has been detected in the pancreas of man (10.3 +/- 2.6 pmol/g), dog (6.5 +/- 1.1 pmol/g), guinea-pig (5.8 +/- 0.9 pmol/g) and rat (0.7 +/- 0.1 pmol/g) using a specific radioimmunoassay. Chromatographic analysis of the pancreatic extracts by high performance liquid chromatography indicated that both guinea-pig and rat have a molecular form of the immunoreactivity which is distinct from the porcine intestinal peptide histidine-isoleucine.
The objective of this study was to develop a radioimmunoassay for PHI and use this to assess its intramural distribution in the human intestine. The antibody was harvested following immunization with porcine PHI conjugated to bovine serum albumin by glutaraldehyde, and the iodinated PHI tracer was prepared by the Iodo-gen method. The assay system showed no cross-reaction with other members of the glucagon-secretin family of peptides and was sensitive to changes of PHI of 2 fmol/tube (95% confidence). High concentrations of immunoreactive PHI were found in the human intestine, exclusively localized in the nonendocrine gut layers, suggesting a possible neuroendocrinological or neurotransmitter role for PHI.
PHI (peptide histidine isoleucine) is a recently identified porcine peptide, present in large quantities in the intestine, which has sequence homologies with VIP, an established intestinal secretagogue, and with secretin, glucagon, and GIP. The effects of PHI on jejunal, ileal, and colonic fluid and electrolyte transport were studied in the pig. PHI appears to be an intestinal secretagogue inducing a reversible net secretion of fluid and electrolytes in jejunum and ileum and less marked effects in the colon.
Endogenous opiates may play a role in regulating intestinal function and we have investigated this possibility in the human upper gastrointestinal tract using loperamide as a locally-acting opiate agonist and naloxone as antagonist. Loperamide (4 mg) had no effect on the fasting pattern of motor activity in the antrum, duodenum and proximal jejunum. However, naloxone (40 micrograms kg-1 h-1, i.v.) abolished interdigestive motor activity in five of ten subjects and reduced antroduodenal motility index per cycle in all subjects (antrum: 1230 +/- 120 to 130 +/- 140 mm2; duodenum: 1120 +/- 150 to 225 +/- 160 mm2; P less than 0.005). These effects were not significantly affected by loperamide. Plasma motilin exhibited cyclic variation with significantly higher concentrations during antroduodenal phase 3 than during phases 1 and 2 of the interdigestive cycle. Plasma motilin was not altered by naloxone or loperamide, and neither drug had any effect on basal gastric acid secretion, duodenal output of amylase and bile salt or duodenogastric reflux. The results suggest that endogenous opiates regulate fasting motor activity in the human gastrointestinal tract but do not influence basal secretory function of the stomach, pancreas or biliary tree.
Explore the source record for details and available documents.
The gut hormone response to a breakfast meal was studied in 12 subjects hospitalised for an episode of acute diarrhoea (presumed infective) who were otherwise well and in 13 healthy control subjects. Fasting blood glucose concentrations were low but basal insulin concentrations were raised. Basal concentrations of pancreatic polypeptide and both basal and postprandial responses of motilin, enteroglucagon, and vasoactive intestinal polypeptide (VIP) were also significantly greater than controls. No abnormalities in plasma concentrations of gastrin, gastric inhibitory polypeptide (GIP) or pancreatic glucagon were found. The suggested physiological actions of the raised hormones may be relevant to the pathophysiology of diarrhoea.
Glucagon-related polypeptides in porcine pancreas and intestine were analysed by gel-permeation chromatography and RIA. Three assays were employed: a nonspecific glucagon assay (R59) of 94% cross-reactivity with glicentin; a pancreatic glucagon assay (RCS5) directed against the C-terminal region of glucagon and of less than 0.01% cross-reactivity with glicentin; and a glicentin assay (R64) of less than 0.01% cross-reactivity with glucagon. For extracts of porcine pancreas all three assays gave similar molar concentrations of immunoreactivity. In porcine intestinal extracts immunoreactivity was detected in significant amounts only by the nonspecific glucagon (R59) and the glicentin (R64) assays, again in similar molar concentrations. The immunoreactivities present in pancreas and intestine were chromatographically and immunologically separable into six main peaks, peaks I, II, III, V, and VI being present in the pancreas, and peaks I, II, and IV in the intestine. The different immunoreactivities of the peaks allowed probable identities to be assigned to their main components. Apart from peak I, which consists of void-volume material that may interfere nonspecifically with the assays, the main components of the peaks can be interpreted as glicentin (in peak II) or fragments derived from glicentin. Peak III contains the N-terminal portion of glicentin (glicentin-related pancreatic peptide), peak IV probably contains glucagon with its 8 amino-acid C-terminal extension, peak V is pancreatic glucagon and peak VI contains smaller N-terminal glicentin fragments. These findings fit with the proposition that glicentin fulfills the role of proglucagon in the pancreas, and is the major component of enteroglucagon in the intestine.