Glucagon-like peptide-1 activates the adenylyl cyclase system in rockfish enterocytes and brain membranes

The role of cutaneous and respiratory heat loss for selective brain cooling in different species is discussed and new experimental results from a comparative study are summarized. In three species (cat, rabbit and rat) the difference between pontine and hypothalamic temperatures was studied as a function of head heat exchanger vasomotion appraised by the difference between hypothalamic and ear pinna (cats and rabbits) or nasal mucosa (rats) temperatures during the behavioral states of wakefulness and slow wave sleep at an ambient temperature of 24+/-1 degrees C. The results show that: (i) the pontine-hypothalamic temperature difference is an useful indicator of selective brain cooling since it is positive and inversely correlated with the hypothalamic-ear pinna temperature difference in cats and rabbits and with the hypothalamic-nasal mucosa temperature difference in rats; (ii) respiratory heat loss prevails quantitatively over cutaneous heat loss in maintaining this difference.     

Glucagon-like peptide-1 reduces hepatic glucose production indirectly through insulin and glucagon in humans

The effect of glucagon-like peptide-1 (GLP-1) on hepatic glucose production and peripheral glucose utilization was investigated with or without infusion of somatostatin to inhibit insulin and glucagon secretion in 13 healthy, non-diabetic women aged 59 years. After 120 min 3-(3)H-glucose infusion, GLP-1 was added (4.5 pmol kg(-1) bolus + 1.5 pmol kg(-1) min(-1)). Without somatostatin (n = 6), GLP-1 decreased plasma glucose (from 4.8 +/- 0.2 to 4.2 +/- 0.3 mmol L(-1), P = 0.007). Insulin levels were increased (48 +/- 3 vs. 243 +/- 67 pmol L(-1), P = 0.032), as was the insulin to glucagon ratio (P = 0.044). The rate of glucose appearance (Ra) was decreased (P = 0.003) and the metabolic clearance rate of glucose (MCR) was increased during the GLP-1 infusion (P = 0.024 vs. saline). Also, the rate of glucose disappearance (Rd) was reduced during the GLP-1 infusion (P = 0.004). Since Ra was reduced more than Rd, the net glucose flow was negative, which reduced plasma glucose. Somatostatin infusion (500 microg h(-1), n = 7) abolished the effects of GLP-1 on plasma glucose, serum insulin, insulin to glucagon ratio, Ra, Rd, MCR and net glucose flow. The results suggest that GLP-1 reduces plasma glucose levels mainly by reducing hepatic glucose production and increasing the metabolic clearance rate of glucose through indirectly increasing the insulin to glucagon ratio in healthy subjects.     

Glucagon-like peptide-1 can reverse the age-related decline in glucose tolerance in rats

Wistar rats develop glucose intolerance and have a diminished insulin response to glucose with age. The aim of this study was to investigate if these changes were reversible with glucagon-like peptide-1 (GLP-1), a peptide that we have previously shown could increase insulin mRNA and total insulin content in insulinoma cells. We infused 1.5 pmol/ kg-1.min-1 GLP-1 subcutaneously using ALZET microosmotic pumps into 22-mo-old Wistar rats for 48 h. Rat infused with either GLP-1 or saline were then subjected to an intraperitoneal glucose (1 g/kg body weight) tolerance test, 2 h after removing the pump. 15 min after the intraperitoneal glucose, GLP-1-treated animals had lower plasma glucose levels (9.04+/-0.92 mmol/liter, P < 0.01) than saline-treated animals (11.61+/-0.23 mmol/liter). At 30 min the plasma glucose was still lower in the GLP-1-treated animals (8.61+/-0.39 mmol/liter, P < 0.05) than saline-treated animals (10.36+/-0.43 mmol/liter). This decrease in glucose levels was reflected in the higher insulin levels attained in the GLP-1-treated animals (936+/-163 pmol/liter vs. 395+/-51 pmol/liter, GLP-1 vs. saline, respectively, P < 0.01), detected 15 min after glucose injection. GLP-1 treatment also increased pancreatic insulin, GLUT2, and glucokinase mRNA in the old rats. The effects of GLP-1 were abolished by simultaneous infusion of exendin [9-39], a specific antagonist of GLP-1. GLP-1 is therefore able to reverse some of the known defects that arise in the beta cell of the pancreas of Wistar rats, not only by increasing insulin secretion but also by inducing significant changes at the molecular level.     

Glucagon-like peptide-2 inhibits centrally induced antral motility in pigs

BACKGROUND: Many individuals develop telangiectases on the face as they mature. The causative factors are numerous. Telangiectases are cosmetically concerning for many of those who are affected. Because of the ability to selectively target vessels, lasers have recently become the focus for treating small facial telangiectases. OBJECTIVE: The purpose of this study was to evaluate the efficacy of the diode-pumped frequency-doubled Q-switched neodymium: ytterium-aluminum-garnet (FD QSNd:YAG) laser (532 nm) for the treatment of telangiectases on the face. METHODS: The diode-pumped FD QSNd:YAG laser (532 nm, 400-micron spot size, 24-msec pulse train) was used to treat telangiectases on the face of 30 adult subjects. Patients were treated once, and clinical improvement and potential adverse effects were assessed at 4 and 8 weeks after treatment. RESULTS: One session of diode-pumped FD QSNd:YAG laser treatment either improved or totally cleared all treated facial telangiectases. CONCLUSION: The diode-pumped FD QSNd:YAG laser is effective for treating small facial telangiectases. An advantage of this laser is that it does not produce postoperative purpura.     

Glucagon-like peptide 1 (GLP-1): a potent gut hormone with a possible therapeutic perspective

This paper narrates Dr Héctor R Croxatto and collaborators' efforts over the past 50 years in search for peptidic hormones obtained by pepsin hydrolysis of blood plasma substrates. In the forties, Croxatto described three peptidic fractions characterized by their hypertensive, oxytocic and antidiuretic properties, designated as pepsitensin, pepsitocin and pepsanurin, respectively. While pepsitensin and pepsitocin were later identified as angiotensin I and metlys-bradykinin, pepsanurin was not identified and its research was halted for 35 years. During that time, Prof Croxatto and his group worked mostly on the renal kallikrein-kinin system, studying its physiological anti-hypertensive role, making significant contributions in the field of renovascular hypertension. After the discovery of atrial natriuretic peptide, Croxatto resumed his work with pepsanurin. In a series of papers from 1988 to 1998, it was shown that: 1) when injected intraperitoneally or in the intestinal lumen of anesthetized rats, or in the isolated perfused rat kidneys, pepsanurin is a potent inhibitor of the natriuretic effect of ANP; 2) plasma kininogens are identified as the substrates for pepsanurin formation; 3) bradykinin and prokinins exert the anti-ANP effect when injected either intravenously, intraperitoneally or intraduodenally, at small non-vasodilator doses; endogenous kinins also block ANP renal excretory effects; 4) a 20-amino acid peptide released by pepsin from domain 1 of purified LMW kininogen was isolated by Croxatto and collaborators, designed as PU-D1, and shown to exert similar anti-ANP effects as pepsanurin or kinins, but being more potent and longer lasting; 5) the anti-ANP effect of pepsanurin, kinins and PU-D1 is mediated by B2 kinin receptors, since it is blocked by a bradykinin receptor antagonist. Currently, Dr Croxatto is working on the hypothesis that intestinal-borne kinins and/or PU-D1 may reduce renal excretion during the prandial cycle.     

Recombinant growth hormone: a new cardiovascular drug therapy

GH has an important role in normal cardiovascular physiologic functioning, working indirectly through effects on IGF-1. An excess or deficiency of GH causes an increased rate of cardiovascular disease, including cardiomyopathy. A relative GH deficiency in older subjects may also increase cardiovascular morbidity and mortality risk. In replacement doses, GH can enhance myocardial contractility; can decrease peripheral vascular resistance; and can reduce total cholesterol and LDL-cholesterol values and fibrinogen and PAI levels. These effects of GH, coupled with the ability to improve skeletal muscle function and reduce adiposity, make it an attractive treatment for patients with CHF and a potential maintenance drug for elderly people. Clinical trials, including studies with GHRH that may reduce the adverse effects of GH therapy, such as hyperglycemia and hypertension, are now in progress.     

Glucagon-like peptide 1 (GLP-1) as a new therapeutic approach for type 2-diabetes

Glucagon-like peptide 1 (GLP-1) is a physiological incretin hormone in normal humans explaining in part the augmented insulin response after oral versus intravenous glucose administration. In addition, GLP-1 also lowers glucagon concentrations, slows gastric emptying, stimulates (pro)insulin biosynthesis, reduces food intake upon intracerebroventricular administration in animals, and may, in addition, enhance insulin sensitivity. Therefore, GLP-1, in many aspects, opposes the Type 2-diabetic phenotype characterized by disturbed glucose-induced insulin secretory capacity, hyperglucagonaemia, moderate insulin deficiency, accelerated gastric emptying, overeating (obesity) and insulin resistance. The other incretin hormone, gastric inhibitory polypeptide (GIP), has lost almost all its activity in Type 2-diabetic patients. In contrast, GLP-1 glucose-dependently stimulates insulin secretion in diet- and sulfonylurea-treated Type 2-diabetic patients and also in patients under insulin therapy long after sulfonylurea secondary failure. Exogenous administration of GLP-1 ([7-37] or [7-36 amide]) in doses elevating plasma concentrations to approximately 3-4 fold physiological postprandial levels fully normalizes fasting hyperglycaemia in Type 2-diabetic patients. The half life of GLP-1 is too short to maintain therapeutic plasma levels for sufficient periods by subcutaneous injections. Current research activities aim at finding GLP-1 analogues with more suitable pharmacokinetic properties than the original peptide. Another approach could be the augmentation of endogenous release of GLP-1, which is abundant in L cells of the lower small intestine and the colon. Interference with sucrose digestion using alpha-glucosidase inhibition moves nutrients into distal parts of the gastrointestinal tract and, thereby, prolongs and augments GLP-1 release. Enprostil, a prostaglandin E2 analogue, fully suppresses GIP responses, while only marginally affecting insulin secretion and glucose tolerance after oral glucose, suggesting compensatory hypersecretion of additional insulinotropic peptides, possibly including GLP-1. Given the large amount of GLP-1 present in L cells, it appears worthwhile to look for more agents that could 'mobilize' this endogenous pool of the 'antidiabetogenic' gut hormone GLP-1.     

The ob gene product (leptin)--a new hormone of adipose tissue

Obesity--an important problem in modern societies--is caused by energy balance dysregulation and produces numerous adverse effects on health. Recently a particular attention has been paid to molecular and physiological mechanisms in the development of obesity and to the signalling role of adipose tissue in energy stores maintenance on the hypothalamic level. Leptin, the obese gene product discovered in 1995, may play a key role in the feedback system between adipose tissue and the ventromedial nucleus of the hypothalamus (satiety centre). The level of ob gene expression in adipose tissue and plasma leptin concentrations in humans are highly correlated with BMI. So far no mutations in the ob gene in obese subjects have been reported therefore leptin molecule could be active. Despite markedly increased leptin levels found in obesity its central action decreasing food intake and increasing energy expenditure is hindered. Defective ob protein signalling to the brain may be due to receptor and post-receptor defects. Neuropeptide Y, the hypothalamic neurotransmitter involved in the maintaining of energy homeostasis, is a likely candidate for mediating leptin afferent signals. In adipose tissue, the level of ob mRNA is regulated by insulin and glucocorticoids--hormones responsible for glucose homeostasis as well as for the central regulation of feeding behaviour. Until now the character of interactions between leptin and other hormones that regulate energy balance is not known, neither is the exact nature of leptin hypothalamic receptor defect. Defining of the role of leptin in the regulation of satiety and energy expenditure will undoubtedly contribute to a better understanding of the pathogenesis of obesity and its related metabolic complications and may lead to a new treatment approach to human obesity based on leptin or its analogues. At present research work focuses on leptin receptor studies and on ob gene polymorphism and its expression in feeding disorders including obesity and anorexia nervosa. The ob gene is one of a few genes involved in energy balance, however, very promising one.     

Glucagon-like peptide-1 retards gastric emptying and small bowel transit in the rat: effect mediated through central or enteric nervous mechanisms

This study investigated effects of glucagon-like peptide-1(7-36)amide (GLP-1) on gastric emptying, small intestinal transit, and contractility of smooth muscle strips in rats. GLP-1 at doses of 10 and 20 pmol/kg/min administered intravenously dose-dependently retarded transit of the small intestine (P < 0.001), while only the higher dose of 20 pmol/kg/min retarded gastric emptying (P < 0.01). GLP-1 at concentrations up to 10(-4) M did not affect the basal tone or contractility of the gastrointestinal muscle strips that were stimulated with electric field stimulation or acetylcholine. Our results demonstrate that small intestinal transit seems more sensitive than gastric emptying to inhibition by GLP-1 at physiologic levels in plasma. Furthermore, this inhibition appears to be mediated through central mechanisms rather than through peripheral actions. Thus, GLP-1 is suggested to inhibit gastric emptying and small intestinal transit through an indirect effect via central or enteric nervous mechanisms.     

Structure-function analysis of a series of glucagon-like peptide-1 analogs

We have used NMR in conjunction with measurements of functional bioactivity to define the receptor-binding structure of glucagon-like peptide-1 (GLP-1.) Identification of the important residues for binding was accomplished by the substitution of amino acids at sites that seemed likely, from an examination of the amino acid sequence and from previously published observations, to be important in the three-dimensional (3D) structure of the molecule. Identification of the receptor-bound conformation of GLP-1, because it is a flexible peptide, required constraint of the peptide backbone into a predetermined 3D structure. Constraint was achieved by the introduction of disulfide bonds and specific side chain-side chain cross-links. The biological relevance of the synthetic structure of each rigidified peptide was assessed by measurement of its ability to bind to the receptor present on RINm5F cells and to elicit a functional response, cyclic AMP production. NMR solution structures were obtained for the most biologically relevant of these analogs. The results of this study indicated that the residues necessary for the biological activity of GLP-1 occupy approximately three equally-spaced regions of the peptide 3D structure, at the corners of an equilateral triangle whose sides are, at a minimum estimate, 12-15A.     

Glucagon-like peptide-1 7-36 amide and peptide YY from the L-cell of the ileal mucosa are potent inhibitors of vagally induced gastric acid secretion in man

The level of noise at washer and pouring system stations was estimated in 12 dairy plants in 7 regions of the country (voivodships). dB(A) and dB(Lin) were measured and the octave analysis performed within the range of 31.5-8000 Hz. The examined premises were found to be a source of hazard to hearing in workers. Mean value of the sound level expressed in dB(A) accounted for 90.61 dB at the washer station and 90.22 dB at the pouring system station.     

AILV1 gene from the yeast Arxula adeninivorans LS3--a new selective transformation marker

The ILV1 gene of the yeast Arxula adeninivorans LS3 (AILV1) has been cloned from a genomic library, characterized and used as an auxotrophic selection marker for transformation of plasmids into this yeast. One copy of the gene is present in the Arxula genome, comprising 1653 bp and encoding 550 amino acids of the threonine deaminase. The protein sequence is similar (60.55%) to that of the threonine deaminase from Saccharomyces cerevisiae encoded by the gene ILV1. The protein is enzymatically active during the whole period of cultivation, up to 70 h. Maximal activities, as well as protein concentrations of this enzyme, were achieved after cultivation times of 20-36 h. The AILV1 gene is a suitable auxotrophic selection marker in transformation experiments using an Arxula adeninivorans ilv1 mutant and a plasmid containing this gene, which is fused into the 25S rDNA of Arxula adeninivorans. One to three copies of the linearized plasmid were integrated into the 25S rDNA by homologous recombination. Transformants resulting from complementation of the ilv1 mutation can be easily and reproducibly selected and in addition are mitotically stable. Therefore, the described system is preferred to the conventional selection for hygromycin B resistance.     

Glucagon-like peptide-1-(7-36)amide increases pulmonary surfactant secretion through a cyclic adenosine 3',5'-monophosphate-dependent protein kinase mechanism in rat type II pneumocytes

Glucagon-like peptide-1 (GLP-1) receptor messenger RNA has been identified in cells considered type II pneumocytes that are involved in the synthesis and secretion of the pulmonary surfactant. In an attempt to open new insights into the control of surfactant secretion, we studied the effects of glucagon-related peptides in this process. Accordingly, type II pneumocytes were isolated from Wistar rat lungs and cultured overnight with [methyl-14C]choline, and then the basal and stimulated secretions of [14C]phosphatidylcholine were measured. GLP-1(7-36)amide stimulated phosphatidylcholine secretion in a concentration-dependent manner in the 1-100 nM range; the concentration of the peptide that produced a half-maximal response was 10 nM. Exendin-4 induced similar effects. No changes were observed when GLP-1-(1-37), GLP-2, or exendin-(9-39) was added to the medium. However, the latter reversed the stimulatory effects of GLP-1-(7-36)amide and exendin-4. A study of the mechanism through which GLP-1-(7-36)amide exerts its stimulatory effect was carried out using different agents that are well known stimulants of phosphatidylcholine secretion. GLP-1-(7-36)amide did not produce any change in the stimulatory effect observed with terbutaline or 8-bromo-cAMP, suggesting the involvement of a cAMP-dependent protein kinase in the stimulatory effect of this peptide on phosphatidylcholine secretion. It was further supported by the use of inhibitors of protein kinases and by the stimulation of cAMP production in type II pneumocytes incubated with either GLP-1-(7-36)amide or exendin-4.     

Are we facing a 'post-antibiotic era'?--a review of the literature regarding antimicrobial drug resistance

Since the introduction of antibiotics in the 1940s, antibiotic resistance has become an increasing problem. Today, multiple-antibiotic resistance is commonly associated with a number of clinically important pathogens and is therefore an important issue in clinical nursing practice. Epidemiological studies identify a number of important factors associated with increases in antimicrobial resistance. These include patterns of antimicrobial use, changes in medical and veterinary care and social practices affecting the transmission of microbes. Bacterial mechanisms of antibiotic resistance and the genetics of resistance-gene transfer are explored, with the intention of developing nurses' knowledge and understanding of control measures.     

Intracerebroventricular growth-hormone-releasing peptide-6 stimulates eating without affecting plasma growth hormone responses in rats

The purpose of this study was to determine the effect of intracerebroventricular (i.c.v.) injections of a synthetic, opioid-related hexapeptide, growth-hormone-releasing peptide-6 (GHRP-6), on stimulation of eating by rats and to correlate this aspect of feeding behavior with the peripheral plasma growth hormone (GH) response to the administered peptide. GHRP-6 dissolved in 5 microL of saline was injected into the lateral ventricles of sated, adult, male, Sprague-Dawley rats in doses from 0 pmol (saline only) to 1000 pmol. For 1 hour after injection, the occurrence of eating was noted, and specimens of arterial blood were collected at 0, 15, 30, and 60 minutes. The plasma was assayed for GH. A nearly linear, statistically significant (p < 0.01) dose-response relationship between the dose of GHRP-6 and the incidence of eating was noted. The mean change from baseline of plasma GH during the 60 minutes after injection was not dose-related (p > 0.2, p > 0.1, and p > 0.1 at 15, 30, and 60 minutes, respectively). We conclude that GHRP-6 given intracerebroventricularly to sated, adult, male, Sprague-Dawley rats stimulates eating and suggest that it does so by some mechanism that is independent of its GH-releasing property.     

Photooxidation of troglitazone, a new antidiabetic drug

Troglitazone (CS-045) is a new oral antidiabetic drug reported to be effective in insulin-resistant diabetes and to show antihypertensive effects. Photooxidation of troglitazone gave the quinone and quinone epoxide as the major final stable products. An intermediate observed by NMR spectroscopy was shown to be the hydroperoxydienone, which is moderately stable at room temperature. The rate constant of singlet oxygen quenching by troglitazone is 2.14 x 10(8) M(-1) s(-1) and the reaction rate constant in acetone-d6 is 8.64 X 10(6) M(-1) s(-1). Only the chroman ring of troglitazone reacts with and quenches singlet oxygen significantly, and its reactivity and products are analogous to those of alpha-tocopherol. The reactivity of CS-45 toward singlet oxygen is much larger than that of the related compounds lacking the chroman ring.     

High potency antagonists of the pancreatic glucagon-like peptide-1 receptor

GLP-1-(7-36)-amide and exendin-4-(1-39) are glucagon-like peptide-1 (GLP-1) receptor agonists, whereas exendin-(9-39) is the only known antagonist. To analyze the transition from agonist to antagonist and to identify the amino acid residues involved in ligand activation of the GLP-1 receptor, we used exendin analogs with successive N-terminal truncations. Chinese hamster ovary cells stably transfected with the rat GLP-1 receptor were assayed for changes in intracellular cAMP caused by the test peptides in the absence or presence of half-maximal stimulatory doses of GLP-1. N-terminal truncation of a single amino acid reduced the agonist activity of the exendin peptide, whereas N-terminal truncation of 3-7 amino acids produced antagonists that were 4-10-fold more potent than exendin-(9-39). N-terminal truncation of GLP-1 by 2 amino acids resulted in weak agonist activity, but an 8-amino acid N-terminal truncation inactivated the peptide. Binding studies performed using 125I-labeled GLP-1 confirmed that all bioactive peptides specifically displaced tracer with high potency. In a set of exendin/GLP-1 chimeric peptides, substitution of GLP-1 sequences into exendin-(3-39) produced loss of antagonist activity with conversion to a weak agonist. The results show that receptor binding and activation occur in separate domains of exendin, but they are more closely coupled in GLP-1.