Peptide In Dogs Research Articles

Halothane anesthesia suppresses reflex tachycardia caused by calcitonin gene-related peptide in dogs

Halothane anesthesia suppresses reflex tachycardia caused by calcitonin gene-related peptide in dogs

Myocardial electrophysiological effects of vasoactive intestinal peptide in dogs

Pages H1559–H1565: Alexandros C. Kralios, Fred L. Anderson, and Fany A. Kralios. “Myocardial electrophysiological effects of vasoactive intestinal peptide in dogs.” On p. H1562, the columns of Fig. 4 were identified in reverse in the legend. The correct sentence should read as follows. Columns represent means ± SD of data from 32 sites in each experiment with epicardial (filled bars) (n = 16) and endocardial (hatched bars) (n = 12) mapping.

Myocardial electrophysiological effects of vasoactive intestinal peptide in dogs

Pages H1559–H1565: Alexandros C. Kralios, Fred L. Anderson, and Fany A. Kralios. “Myocardial electrophysiological effects of vasoactive intestinal peptide in dogs.” On p. H1562, the columns of Fig. 4 were identified in reverse in the legend. The correct sentence should read as follows. Columns represent means ± SD of data from 32 sites in each experiment with epicardial (filled bars) ( n = 16) and endocardial (hatched bars) ( n = 12) mapping.

Cardiorenal and neurohumoral effects of endogenous atrial natriuretic peptide in dogs with severe congestive heart failure using a specific antagonist for guanylate cyclase-coupled receptors.

To elucidate the extent of the compensatory role of endogenous atrial natriuretic peptide (ANP) in severe congestive heart failure (CHF), we examined the changes in hemodynamics and neuroendocrine and renal functions after incremental administration of an ANP antagonist, HS-142-1 (HS), in dogs with CHF. We assessed the effects of HS on the suppression of plasma and urinary cGMP levels as a marker of endogenous ANP activity in dogs without CHF. Bolus injections of 0.3 and 1.0 mg/kg HS reduced plasma cGMP levels to 77% and 60% and urinary cGMP excretion to 78% and 61% of the relevant control levels, respectively. Then the study was performed in dogs with CHF induced by chronic rapid ventricular pacing, and the plasma ANP level was sixfold higher than that in the controls. Hemodynamic, hormonal, and renal variables were determined both before and after subsequent incremental administration (0.3, 1.0, and 3.0 mg/kg every 30 minutes) of HS. HS lowered the plasma and urinary cGMP levels dose dependently to 32% and 37% of the control levels, respectively. Mean arterial, pulmonary capillary wedge, and right atrial pressures and cardiac output did not change significantly. However, plasma renin activity, aldosterone level, and norepinephrine level increased rapidly to 226%, 179%, and 252% of the control values, respectively. Urine flow rate and urinary sodium excretion were significantly inhibited, with no concomitant change in glomerular filtration rate or renal plasma flow. These findings suggest that endogenous ANP contributes to the suppression of the activation of the renin-aldosterone system and sympathetic nervous activity and body fluid retention but that the vasodilative action of this peptide is attenuated in advanced CHF.

Identification of xenin, a xenopsin-related peptide, in the human gastric mucosa and its effect on exocrine pancreatic secretion.

One of the peptides previously discovered in amphibians is the octapeptide xenopsin. As immunohistochemistry has also indicated the presence of xenopsin immunoreactivity in man, we extracted in the present investigation xenopsin-immunoreactive material from human gastric mucosa and purified it to homogeneity with several high performance liquid chromatography (HPLC) reverse phase and ion exchange chromatographic steps. The eluates were monitored with a radioimmunoassay for amphibian xenopsin. Determination of the amino acid sequence revealed a 25-amino acid peptide having 6 C-terminal amino acids in common with amphibian xenopsin. The sequence of this peptide, termed xenin 25, is M-L-T-K-F-E-T-K-S-A-R-V-K-G-L-S-F-H-P-K-R-P-W-I-L. The peptide was custom-synthesized. Mass spectrometry of the synthetic and the extracted peptide revealed identical molecular mass. Purification of 250 ml of human postprandial plasma with Sep-Pak C18 cartridges, reverse phase HPLC, and ion exchange chromatography demonstrated circulating xenin immunoreactivity at a retention time identical to xenin 25. The amount of xenin immunoreactivity at the position of xenin 25 on C18-HPLC increased significantly after a meal. A radioimmunoassay utilizing antibodies to xenin 25 and a 125I-labeled analogue of xenin 25 was used to measure immunoreactive xenin in the plasma of 10 volunteers. There was a significant rise of xenin immunoreactivity in the plasma after a meal. Intravenous infusion of the synthetic peptide in dogs stimulated exocrine pancreatic secretion beginning at a dose of 4 pmol/kg/min. The maximal effect was seen with 64 pmol/kg/min. We have detected, therefore, a new peptide, xenin 25, in human gastric mucosa; we have provided evidence for the presence of this peptide in the human circulation, and have shown a rise of plasma xenin concentrations after a meal. This peptide stimulates exocrine pancreatic secretion. Its physiologic role deserves further investigation.

Myocardial electrophysiological effects of vasoactive intestinal peptide in dogs

Vasoactive intestinal peptide (VIP) is a potent inotrope and coronary vasodilator. To test whether VIP also exerts regional myocardial electrophysiological (EP) effects, dose-response and time-course effects of intracoronary injections (10(-10)-10(-4) M) were obtained in 4 intact hearts and 12 in situ normoperfused right ventricular flap preparations in chloralose-anesthetized dogs. Under constant rate, activation (A), recovery (R), and A-R interval (ARI) maps were constructed from multiplexed unipolar surface electrograms recorded simultaneously from 32 sites. Effects were compared with those of isoproterenol (Iso) and forskolin (For). The main finding with all agonists was the uniform shortening of ARIs in a dose-response fashion with a maximum of 30 +/- 4 ms or 20% from control. Although the maximal EP changes were similar for all agonists, they occurred at different molecular concentrations (10(-6) Iso, 10(-5) VIP, and 10(-4) For). Also, whereas the duration of EP effect did not exceed 5 min for Iso and For, it was markedly sustained for VIP, outlasting its contractile but paralleling its vasodilatory effect. The physiological endoepicardial differences in ARI and the recovery sequence were preserved for all agonists. Thus VIP, in addition to coronary vasodilation and myocardial inotropy, exerts a strong balanced global myocardial EP effect, similar to, but more sustained than, the adrenergic effect. The difference in duration of inotropic and EP effects may point to different mediating mechanisms.

Urinary excretion of cGMP in response to atrial natriuretic peptide in dogs with acute pancreatitis

Previous studies have shown that when atrial natriuretic peptide (ANF) is given to anaesthetized dogs with hypovolemic acute pancreatitis, it will produce a diuresis and natriuresis but will not elevate the glomerular filtration rate (GFR). When the same dose of peptide is given to dogs equally hypovolemic (hemorrhage) but without pancreatitis, a brisk increment in GFR occurs. GFR will, however, rise in dogs with pancreatitis in response to other peptides, such as glucagon. In these studies we assessed cGMP excretion as a marker for ANF effect in both normal anaesthetized dogs and dogs with acute experimental pancreatitis. In each group, urinary output and sodium excretion increased significantly, but GFR rose only in the control group. Urinary excretion of cGMP rose equally and dramatically in both control and experimental animals. We conclude that GFR is prevented from rising in dogs with experimental pancreatitis following ANF, but this effect does not depend on depressed cGMP generation.

Response to atrial natriuretic peptide in dogs with hypovolemic acute pancreatitis

The ability of atrial natriuretic peptide (ANP) to preserve renal function in dogs with hypovolemic acute renal insufficiency was tested in anesthetized dogs 4 h after the induction of acute pancreatitis. Plasma volume had decreased by 21.5% and glomerular filtration rate (GFR) by 43.2%. Blood pressure had declined by 30 mmHg. ANP was given intravenously at 50 and 150 ng.kg-1.min-1. With the lower dose, blood pressure (BP), GFR, and clearance of p-aminohippuric acid (CPAH) did not change but urine flow (V) and sodium excretion (UNaV) increased. With the higher dose, BP declined by 25 mmHg, GFR declined, but V and UNaV still increased. When plasma volume was maintained with 4% colloid during the progression of pancreatitis and ANP 50 ng.kg-1.min-1 given, BP declined, GFR did not change, and there was a magnified increment in V and UNaV. The administration of glucagon (5 micrograms/min iv) to dogs with hypovolemic pancreatitis caused BP to decline by 17 mmHg. Despite a major increment in GFR, fractional excretion of sodium increased only slightly, compared with that obtained with ANP. We conclude that glucagon preserves GFR more effectively than ANP in hypovolemia, but ANP is more effective in protecting urinary water and sodium excretion.

Renal and hemodynamic effects of synthetic atrial natriuretic peptide in dogs with chronic renal failure.

The present experiments were performed to clarify the renal and hemodynamic effects of atrial natriuretic peptide (ANP) in dogs with chronic renal failure (CRF; produced by 5/6 nephrectomy 3-4 weeks before study). Synthetic alpha-hANP was administered intravenously (0.1 micrograms/kg body weight for 30 min) with a priming bolus injection (1.0 micrograms/kg body weight) to anesthetized controls (n = 8) and CRF-dogs (n = 10). The effects of ANP on renal function, cardiac function, lithium clearance, and plasma ANP levels during clearance studies were determined. Effects of ANP on the hemodynamics were observed to the same degree in both groups. An increase in inulin clearance (CIn) was noted only in the CRF-dogs (7.5 +/- 2.1 to 9.6 +/- 2.9 ml/min; p less than 0.01). The infusion of ANP increased the urine volume, absolute sodium excretion, and osmolar clearance in the control and CRF groups. The fractional excretion of lithium (FELi), a marker of the proximal reabsorption of sodium, was higher at baseline in the CRF group (control group, 24.4 +/- 6.7 vs. CRF group, 41.5 +/- 13.2%; p less than 0.001). Following ANP infusion, FELi increased in both groups. The plasma ANP levels were monitored during the clearance study, and those of the CRF group were higher throughout the experiments. Thus, extrinsic ANP induced diuresis and natriuresis in CRF-dogs, produced by nephron mass reduction. Discrepancies in the pattern of response and plasma ANP levels were observed between the controls and CRF-dogs, suggesting that the action and metabolic clearance rate of ANP were altered in the CRF state.

Renal hemodynamic response to intrarenal infusion of calcitonin gene-related peptide in dogs.

The renal hemodynamic and excretory effects of intrarenal infusions of synthetic beta-human calcitonin gene-related peptide (beta-hCGRP) were examined in normal sodium replete dogs (Group 1, n = 6), in sodium replete dogs pretreated with indomethacin (Group 2, n = 6), and in sodium deplete dogs (Group 3, n = 5). In all groups of anesthetized dogs beta-hCGRP was infused at 5 and 10 ng.kg-1.min-1 for 50 min periods each. In the sodium replete group, beta-hCGRP infusions strikingly increased renal blood flow, but this response was markedly attenuated in the other 2 groups. During beta-hCGRP infusions, the clearance of creatinine also increased significantly in the sodium replete and deplete groups, but not in the indomethacin pretreated animals. No consistent changes in urinary sodium excretion or plasma renin activity were observed with beta-hCGRP infusions in any of the 3 groups of dogs. These results indicate that beta-hCGRP is a potent renal vasodilator and can increase renal blood flow and glomerular filtration. The data also suggest that the renal hemodynamic actions of beta-hCGRP are partially mediated by renal prostaglandins, and that the vasodilatory effects of beta-hCGRP may be antagonized by high circulating levels of endogenous angiotensin II in sodium-volume depletion. Finally, beta-hCGRP does not appear to have significant actions on urinary sodium excretion or plasma renin activity under the experimental conditions of the present study.

Changes in plasma calcium and in radiocalcium kinetics after termination of 5-week infusions of synthetic parathyroid peptide in dogs.

Nine dogs were infused at constant rates with the synthetic parathyroid peptide hPTH 1-34 (initially sc) to produce consistent hypercalcaemia. Over the final week, the infusions were iv. Radioisotopic tracers were injected iv 30 days (5 dogs) and 2 days (9 dogs) before the infusions were suddenly terminated. In 5 dogs, complete urine collections were obtained via a bladder catheter over 8 h beginning 2 h before stopping the infusions. Cessation of treatment caused small rises in the urinary Ca: creatinine ratio. Plasma calcium levels fell by a mean of 0.44 mmol/l, of which total urine calcium excretion only accounted for 55%. Immediately after the PTH infusions were stopped, consistent but transient increases were seen in the ratio of 'new' 47Ca to 'old' 45Ca label, suggesting inflow of 40Ca of high 47Ca specific activity from a fairly rapidly exchangeable bone pool. These data confirm and extend previous evidence that the immediate response of the calcium equilibrium between bone and bloodstream to rapid changes in plasma PTH concentrations in the supra-physiological range is paradoxical relative to the classical later response.

Radioimmunoassay study of hepatic clearance and disappearance half-time of somatostatin and vasoactive intestinal peptide in dogs.

The effects of hepatic transit on concentrations of synthetic cyclic (ovine) somatostatin and of highly purified (porcine) vasoactive intestinal peptide were studied in five conscious dogs prepared with indwelling portal catheters. The peptides were infused via peripheral vein catheters or the portal catheters for 40 minutes at actual integrated doses of 2.8 pmol/kg/min for vasoactive intestinal peptide an 8.2 pmol/kg/min for somatostatin. Specific radioimmunoassays were used for the measurement of the circulating peptides. As estimated from the plateau peptide concentrations achieved a hindleg vein during the portal and the peripheral infusions, the transhepatic loss of immunoreactive vasoactive intestinal peptide was 72.9 +/- 2.1%, against 27.5 +/- 12.5% for somatostatin. For the given doses of peptides infused systematically, the half-life, metabolic clearance rate, and distribution volume were, respectively, 1.80 +/- 0.1 minutes, 39.3 +/- 5.2 ml/kg/min, and 103.7 +/- 14.8 ml/kg for vasoactive intestinal peptide, and 1.0 +/- 0.2 minutes, 95.2 +/- 12.5 ml/kg/min, and 114.7 +/- 6.0 ml/kg for somatostatin. These results indicate that (ovine) somatostatin and (porcine) vasoactive intestinal peptide are both readily cleared from plasma in dogs. In the present experimental conditions, vasoactive intestinal peptide, but not somatostatin, was rapidly altered through hepatic transit so that it escaped recognition by the assay system.

Effects of test meal, intragastric nutrients, and intraduodenal bile on plasma concentrations of immunoreactive somatostatin and vasoactive intestinal peptide in dogs

Specific radioimmunoassays were used to measure somatostatin and vasoactive intestinal peptide in portal and peripheral plasma from conscious dogs prepared with indwelling portal catheters. In six animals with intact stomachs, a test meal induced a significant rise of portal and peripheral somatostatin, while the significant response of vasoactive intestinal peptide in portal plasma was not reflected in peripheral blood. Similar somatostatin and vasoactive intestinal peptide responses were observed in six dogs previously submitted to antrectomy and Billroth I anastomosis, when given the same test meal, while the gastrin response was 20% of the response in the intact dogs (P < 0.01). The effects of intragastric instillation of 300 ml dextrose, casein hydrolysate, and Intralipid, adjusted to 300 mosmol/kg and pH 7.0, were studied in six dogs with intact stomachs. Casein and Intralipid induced significant increases of somatostatin in portal and peripheral plasma, while VIP increased after Intralipid only, both in portal and peripheral blood. Dextrose resulted in no significant variation of either peptide in portal or in systemic plasma. Intraduodenal infusion of isotonic bile induced a significant release of somatostatin, both in portal and peripheral plasma, but no significant vasoactive intestinal peptide response. These results indicate that several factors can evoke a significant release of somatostatin in dogs, and that the variations of the peptide concentration in portal plasma are reflected in peripheral blood. Among the factors tested, only intragastric fat evoked a vasoactive intestinal peptide response that could be measured in peripheral blood.

Effects of gastrin on circulating levels of somatostatin, pancreatic polypeptide, and vasoactive intestinal peptide in dogs.

The effect of synthetic human gastrin I, infused at two doses, on the concentrations of somatostatin, pancreatic polypeptide, and vasoactive intestinal peptide in portal and systemic blood was studied in six anesthetized dogs. Intragastric pH was maintained at 5.5, and acid output was measured by intragastric titration. Significant increases in somatostatin and pancreatic polypeptide concentrations in portal blood were found with the lower dose of gastrin (0.5 microgram/kg . h) infused for 40 min. When gastrin was infused at 1.5 microgram/kg . h for 100 min, both portal and systemic blood concentrations of somatostatin and pancreatic polypeptide rose significantly. Cimetidine (300 mg, as an iv bolus), given 40 min after the beginning of the second infusion, did not affect gastrin-stimulated release of somatostatin and pancreatic polypeptide, whereas acid output was completely abolished. Vasoactive intestinal peptide concentrations did not change with the infusion of either dose of gastrin. This daily shows that gastrin releases somatostatin and pancreatic polypeptide in a dose-dependent fashion, and since this release was not acid mediated, it appears likely to be a direct action of gastrin.

Central cardiovascular effects of morphinomimetic peptides in dogs

Morphinomimetic peptides were injected into the cisterna magna of chloralosed dogs. Methionine enkephalin (500 μg/kg i.c.) was found ineffective but β-endorphin (50 μg/kg i.c.) induced an initial and transient increase in blood pressure and heart rate followed by a delayed hypotension and bradycardia. The synthetic pentapeptides, [d-ala 2]met-enkephalin (500 μg/kg i.c.), [d-ala 2]met-enkephalinamide (500 μg/kg i.c.) also induced a marked hypotensive, bradycardic and sympatho-inhibitory effect. High doses of naloxone (100 μg/kg i.v.) were requir d to antagonize these effects transiently.

Dispensability of Both the Amide of Phenylalanine and the Carboxyl Group of Aspartic Acid for the Stimulation of Gastric Acid Secretion by Gastrin Peptides in Dogs

Two derivatives of the C-terminal tripeptide of gastrin devoid of -NH2 from the phenylalanyl residue and of -COOH from the aspartic acid, MBOC-Met.Asn.Phe-OH (I) and MBOC-Met.Asp-OBenz.Phe-OMe (II), stimulated gastric acid secretion in the dog when infused intravenously at doses of 100 to 400 mug/kg-hr. Maximal responses induced by I and II were about 30-40% of that induced by the C-terminal tetrapeptide of gastrin. At a dose of 600 mug/kg-hr, I had an inhibitory action while II initially augmented and then inhibited acid production. Neither the C-terminal amide nor the carboxyl group of the aspartyl residue is essential for the gastric stimulatory activity of gastrin peptides.

Antidiuretic responses to neurohypophysial hormones and some of their synthetic analogues in dogs and rats.

The known neurohypophysial hormones and several synthetic analogues containing substituted amino acids in the side chain were injected intravenously into hydra ted dogs and rats. The nature of the amino acid in the penultimate position of the peptide side chain (the 8-position) appears to determine the relative antidiuretic activities of the peptides in dogs and rats. Substitution of lysine for 8-arginine reduces antidiuretic activity in dogs more than in rats. Analogues with an 8-leucine are weak in both dog and rat antidiuretic activities. Peptides containing an 8-arginine moiety cause more prolonged antidiuresis in rats than do their 8- lysine or 8-leucine counterparts. This is not due to differing rates of disappearance of these peptides from the circulation.