T.J. McDonald

Galanin - a novel biologically active peptide from porcine intestine

The isolation of a novel biologically active peptide, designated galanin, is described. The peptide was discovered by the detection of its C‐terminal amide structure in porcine intestinal extract using a chemical method. It was found that galanin consists of 29 amino acids and the complete amino acid sequence is: contract smooth muscle preparations from the rat and to cause a mild and sustained hyperglycemia in dog.

Galanin Inhibits Insulin Secretion and Induces Hyperglycemia in Dogs

Intravenous administration of galanin into fasted conscious dogs produced a dose-dependent hyperglycemia accompanied by decreases in plasma insulin levels, but with no elevation of plasma glucagon levels. Galanin infusions produced greater parenteral glucose-induced rises in plasma glucose levels along with markedly blunted insulin responses compared with glucose and insulin responses to control glucose infusions. Immediately after cessation of the galanin infusions, elevation of plasma insulin levels occurred in the basal state and after parenteral glucose loading. These results suggest that galanins hyperglycemic activity is predominantly mediated by a reversible inhibition of insulin secretion.

Glucagon-Like Peptide I Reduces Postprandial Glycemic Excursions in IDDM

Effects of human glucagon-like peptide I (GLP-I)(7–36)amide were examined in volunteers having insulin-dependent diabetes mellitus (IDDM) with residual C-peptide (CP) secretion (n = 8, 7 men and 1 woman; age, 31 ± 1.4 years; body mass index, 24.7 ± 0.7 kg/m2; duration of diabetes, 3.2 ± 0.8 years; insulin dose, 0.41 ± 0.05 U · kg−1· day−1; meal-stimulated CP, 1.0 ± 0.2 nmol/l [means ± SE]). After a mixed meal (Sustacal, 30 kJ/kg body wt), intravenous injection of GLP-I, 1.2 pmol · kg−1 · min−1 through 120 min, virtually abolished increments of plasma glucose, CP, pancreatic polypeptide (PP), and glucagon concentrations, with no significant effect on plasma gastrin levels during the infusions. At reduced dosage (0.75 pmol · kg−1 · min−1), GLP-I had lesser effects on plasma glucose and CP levels. On cessation of intravenous GLP-I infusions after the meals, plasma glucose, CP, PP, and glucagon concentrations rebounded toward control levels by 180 min, and the response of plasma gastrin was prolonged. These rebound responses are consistent with intestinal delivery of food retained in the stomach on escape from inhibition of gastric emptying by GLP-I. Infusion of 1.2 pmol · kg−1 · min−1 GLP-I with 20 g glucose (10% dextrose in water) injected intravenously over 60 min enhanced plasma responses of immunoreactive CP; the mean incremental areas under concentration curves (0–60 min) increased sixfold, but the glycemic excursion was not affected. Thus, in CP-positive IDDM, pharmacological doses of GLP-I reduce glycemic excursions after meals by a mechanism(s) not dependent on stimulation of insulin secretion, presumably involving delayed gastric emptying. This effect of the peptide on blood glucose levels after meals may have therapeutic implications in both IDDM and non-insulin-dependent diabetes.

Aberrant expression of gastrin-releasing peptide and its receptor by well-differentiated colon cancers in humans

Epithelial cells lining the adult human colon do not normally express gastrin-releasing peptide (GRP) or its receptor (GRPR). In contrast, approximately one-third of human colon cancers and cancer cell lines have been shown to express GRP-binding sites. Because GRPR activation causes the proliferation of many cancer cell lines, GRP has been presumed to act as a clinically significant growth factor. Yet GRP has not been shown to be expressed by colon cancers in humans nor has the effect of GRP and/or GRPR coexpression on tumor behavior been investigated. We therefore determined GRP and GRPR expression by immunohistochemistry in 50 randomly selected colon cancers resected between 1980 and 1997, all 37 associated lymph node and liver metastases, and 20 polyps. Tumor sections studied were those that contained the margin and adjacent nonmalignant epithelium. Overall, 84% of cancers aberrantly expressed GRP or GRPR, with 62% expressing both ligand and receptor, whereas expression was not observed in adjacent normal epithelium. Consistent with the previously established mitogenic capabilities of GRP, tissues coexpressing GRP and GRPR were more likely to express proliferating cell nuclear antigen than tissues not expressing both ligand and receptor. Yet GRP/GRPR coexpression was seen with equal frequency in stage A as in stage D cancers and was only detected in 1 in 37 metastases. Furthermore, Kaplan-Meier analysis did not reveal any difference in patient survival between those whose tumors did or did not express GRP/GRPR. In contrast, GRP/GRPR coexpression was found in all well-differentiated tumor regions, whereas poorly differentiated tissues never coexpressed GRP/GRPR. Overall, these data indicate that, although GRP is a mitogen, it is not a clinically significant growth factor in human colon cancers. Rather, the strong association of GRP/GRPR coexpression with tumor differentiation raises the possibility that these proteins primarily act in vivo as morphogens.Epithelial cells lining the adult human colon do not normally express gastrin-releasing peptide (GRP) or its receptor (GRPR). In contrast, approximately one-third of human colon cancers and cancer cell lines have been shown to express GRP-binding sites. Because GRPR activation causes the proliferation of many cancer cell lines, GRP has been presumed to act as a clinically significant growth factor. Yet GRP has not been shown to be expressed by colon cancers in humans nor has the effect of GRP and/or GRPR coexpression on tumor behavior been investigated. We therefore determined GRP and GRPR expression by immunohistochemistry in 50 randomly selected colon cancers resected between 1980 and 1997, all 37 associated lymph node and liver metastases, and 20 polyps. Tumor sections studied were those that contained the margin and adjacent nonmalignant epithelium. Overall, 84% of cancers aberrantly expressed GRP or GRPR, with 62% expressing both ligand and receptor, whereas expression was not observed in adjacent normal epithelium. Consistent with the previously established mitogenic capabilities of GRP, tissues coexpressing GRP and GRPR were more likely to express proliferating cell nuclear antigen than tissues not expressing both ligand and receptor. Yet GRP/GRPR coexpression was seen with equal frequency in stage A as in stage D cancers and was only detected in 1 in 37 metastases. Furthermore, Kaplan-Meier analysis did not reveal any difference in patient survival between those whose tumors did or did not express GRP/GRPR. In contrast, GRP/GRPR coexpression was found in all well-differentiated tumor regions, whereas poorly differentiated tissues never coexpressed GRP/GRPR. Overall, these data indicate that, although GRP is a mitogen, it is not a clinically significant growth factor in human colon cancers. Rather, the strong association of GRP/GRPR coexpression with tumor differentiation raises the possibility that these proteins primarily act in vivo as morphogens.

Characterization of an avian gastric (proventricular) peptide having sequence homology with the porcine gastrin-releasing peptide and the amphibian peptides bombesin and alytesin

Bombesin, a peptide with 14 amino acid residues, was isolated from the skin of an European frog [I ] and has been the subject of many recent investigations due to its diverse and potent pharmacological effects on the mammalian gastro-intestinal tract, pancreas, and central nervous system (reviewed [2,3]). We have reported the sequence of a 27 residue porcine gastrin-releas~g peptide (GRP) with marked C-terminal homology with bombesin [4]. Subsequent investigations indicate that natural porcine GRP and synthetic bombesin on intravenous administration, share the property of elevating plasma gastro-intestinalpancreatic hormone levels [Sf and that a synthetic replicate of GRP and bombesin on intracranial administration produce similar pharmacological effects [6]. Immunological evidence indicated that the avian proventriculus was an abundant source of bombesin-like immunoreactivity [7-91. We therefore began an investigation of extracts of the chicken proventriculus and report here the isolation and amino acid sequence of a 27 residue chicken proventricular peptide having marked sequence homology with the porcine GRP and the amphibian peprides bombesin and alytesin.

Hyperplasia of Bombesin-Immunoreactive Pulmonary Neuroendocrine Cells and Neuroepithelial Bodies in Sudden Infant Death Syndrome

The distribution and frequency of bombesin immunoreactive neuroendocrine (NE) cells including neuroepithelial bodies (NEB) was analyzed morphometrically in lung sections from 25 infants who died of sudden infant death syndrome (SIDS) and 25 control infants. The control group included infants age-matched to those with SIDS, as well as subjects ranging in age from early to late infancy, to define the postnatal development of pulmonary NE-cell system. Quantitative analysis was performed on lung sections immunostained with monoclonal antibody against bombesin and the contents of bombesin-like peptide in lung extracts were measured by a specific radioimmunoassay (RIA). In control infants, the frequency of NE cells was high at birth but decreased dramatically during the first year of life. In SIDS infants, the frequency of NE cells, the size of NEB, and the mean concentration of bombesin-like peptide detected by RIA were significantly increased compared to those values for age-matched controls. These findings suggest hyperplasia of bombesin-immunoreactive NE-cell system in the lungs of SIDS infants. Since NEB are thought to function as hypoxia-sensitive airway chemoreceptors and since these cells are prominent in the neonates but decline postnatally, we speculate that chronic hypoxia and/or developmental delay may be responsible for this alteration in the lungs of SIDS victims. Potential dysfunction of pulmonary NE-cell system, compounded by other abnormalities in the autonomic regulation of respiration may be of importance in the pathogenesis of SIDS.

Actions of galanin fragments on rat, guinea-pig, and canine intestinal motility

The 1-20 fragment of synthetic porcine galanin, prepared by tryptic digestion of the intact molecule, was equipotent to synthetic porcine galanin 1-29 in the smooth muscle actions of exciting the rat jejunal longitudinal muscle in vitro and inhibiting circular muscle contractions of the canine small intestine in vitro and in vivo, but was less potent in inhibiting nerve-stimulated contractions of the guinea-pig taenia coli. Fragment 21-29 was effective at high doses only in the canine ileum. Activity of galanin 1-11 was greatly reduced in the dog in vivo. These results may reflect species or cell type differences.

Isolation of a brain peptide identical to the intestinal PHI (peptide HI)

The isolation of a brain peptide identical to the intestinal peptide PHI (peptide HI) is described. The peptide was isolated from porcine brain extract using a chemical assay method based on its C‐terminal isoleucine amide structure. The complete amino acid sequence of the peptide was found to be: This sequence is identical to the intestinal peptide thus demonstrating PHI to be a brain‐gut peptide. The role of PHI in the central nervous system as a neurotransmitter or neuromodulator is discussed.

Peptide YY stimulates circular muscle contractions of the isolated perfused canine ileum by inhibiting nitric oxide release and enhancing acetylcholine release

Peptide YY (PYY) and neuropeptide Y (NPY), infused into the quiescent isolated perfused canine ileum, dose-dependently increased phasic activity of the circular muscle and decreased tonic output of immunoreactive vasoactive intestinal peptide (VIP) in the venous effluent. The contractions subsided before the prolonged inhibition of VIP output. Motor excitation by PYY, an abundant neuropeptide in this tissue, was reduced by blockade of muscarinic or nicotinic receptors, or inhibition of nitric oxide (NO) synthase, despite continued inhibition of VIP output. A combination of atropine and hexamethonium eliminated the PYY-induced decrement in VIP output and left motor excitation unchanged. Blockade of NO synthase eliminated motility increases under these conditions. Intracellular microelectrode recordings of myenteric plexus-free circular muscle strips found no effect of NPY on the resting membrane potential, or on the field stimulation-induced inhibitory junction potential. Inhibition of VIP release plays no essential role in changing motility. These results suggest that PYY/NPY induce motility by stimulating release of acetylcholine and inhibiting NO release at a locus proximal to but not on nerve terminals.

Macroscopic Healing of Esophagitis Does Not Improve Esophageal Motility

The purpose of the present study was to prospectively determine if healing of esophagitis as assessed by endoscopy results in improved esophageal motility. Thirty-one patients with erosive esophagitis who were randomized to receive either omeprazole 20 mg once daily or placebo completed the double-blind study. All patients underwent endoscopy and esophageal motility before treatment and at four weeks after treatment. Twenty-two healthy volunteers underwent esophageal manometry and served as normal controls. Manometric tracings were coded, randomized, and analyzed blindly. Compared to normal controls, patients with esophagitis had significantly lower LESP, decreased amplitude of peristaltic contractions, and increased occurrence of abnormal contractions. Omeprazole was superior to placebo in healing of esophagitis. However, healing of esophagitis was not associated with any improvement in esophageal motility. The manometric data suggest that the motility disturbance seen in esophagitis is not secondary to the esophagitis but rather a primary phenomenon. The lack of improvement of esophageal motility with healing may explain the high recurrence of esophagitis in clinical trials following discontinuation of omeprazole.The purpose of the present study was to prospectively determine if healing of esophagitis as assessed by endoscopy results in improved esophageal motility. Thirty-one patients with erosive esophagitis who were randomized to receive either omeprazole 20 mg once daily or placebo completed the double-blind study. All patients underwent endoscopy and esophageal motility before treatment and at four weeks after treatment. Twenty-two healthy volunteers underwent esophageal manometry and served as normal controls. Manometric tracings were coded, randomized, and analyzed blindly. Compared to normal controls, patients with esophagitis had significantly lower LESP, decreased amplitude of peristaltic contractions, and increased occurrence of abnormal contractions. Omeprazole was superior to placebo in healing of esophagitis. However, healing of esophagitis was not associated with any improvement in esophageal motility. The manometric data suggest that the motility disturbance seen in esophagitis is not secondary to the esophagitis but rather a primary phenomenon. The lack of improvement of esophageal motility with healing may explain the high recurrence of esophagitis in clinical trials following discontinuation of omeprazole.