Hemodynamic responses to glucagon: an experimental study of central, visceral and peripheral effects

A double-blind, placebo-controlled, single-ascending dose study to evaluate the safety, tolerability, pharmacokinetics, and pharmacodynamics of HM15136, a novel long-acting glucagon analogue, in healthy subjects

AIM

To evaluate the safety and tolerability, pharmacokinetics, and pharmacodynamics of HM15136, a novel long-acting glucagon analogue under development, in healthy males and females presenting with no childbearing potential.

MATERIALS AND METHODS

A randomized, double-blind, placebo-controlled, single-ascending dose study was conducted in 56 subjects who randomly received a single subcutaneous dose of HM15136 or its matching placebo at a ratio of 6:2 at 10, 20, 30, 50, 80, 100, and 120 μg/kg.

RESULTS

All adverse events were mild and transient. Neither serious adverse events nor discontinuation as a result of adverse events occurred. The most frequent adverse drug reaction was nausea (5.3%, only in the 100- and 120-μg/kg groups). HM15136, particularly at doses of 50 μg/kg or higher, increased fasting blood glucose, with a maximum increase and area under the curve of 1.5 mmol/L at day 10 (P = .006) and 166.3 day·mmol/L (P = .022) at the dose of 80 μg/kg, while suppressing the secretion of endogenous glucagon, which continued until day 17. HM15136 also significantly reduced gluconeogenic and ketogenic amino acids. Compensatory changes in endogenous insulin and incretin hormones by HM15136 were not apparent. HM15136 was slowly but steadily absorbed and reached a peak concentration at 46-68 hours after a single subcutaneous injection. HM15136 was eliminated with a terminal phase half-life of 77.1-101.1 hours.

CONCLUSIONS

A single subcutaneous dose of HM15136 at 10-120 μg/kg was safe and well tolerated. The long half-life of HM15136, coupled with an increase in blood glucose for ~2 weeks, may warrant a weekly dosing regimen.

Interactions of exendin-(9-39) with the effects of glucagon-like peptide-1-(7-36) amide and of exendin-4 on arterial blood pressure and heart rate in rats

This study was designed to determine the interactions of peptide exendin-(9-39) with the effect of glucagon-like peptide-1-(7-36) (GLP-1 (7-36)) amide and of exendin-4 on arterial blood pressure and heart rate in the rat. Both GLP-1 (7-36) amide and exendin-4 produced a dose-dependent increase in systolic, diastolic and mean arterial blood pressure, as well as in heart rate, although the effect of exendin-4 was more prolonged. These data indicate a longer functional half-life in vivo for exendin-4 as compared to GLP-1 (7-36) amide, which may have therapeutical applications. The antagonist effect of exendin-(9-39) on these cardiovascular parameters was also tested with 3000 ng of exendin-(9-39) intravenously administered 5 min before i.v. injection of 10 ng of either GLP-1 (7-36) amide or exendin-4. Under these experimental conditions the effect of the latter two peptides on arterial blood pressure and heart rate was blocked. By contrast, single administration of exendin-(9-39) did not modify cardiovascular parameters. These findings indicate that exendin-4 is an agonist and that exendin-(9-39) is an antagonist of the action of GLP-1 (7-36) amide on arterial blood pressure and heart rate. Therefore, the action of GLP-1 (7-36) amide on these parameters seems to be mediated through its own receptors.

Changes in arterial blood pressure and heart rate induced by glucagon-like peptide-1-(7-36) amide in rats

This study was designed to determine the effects of glucagon-like peptides (GLP) on arterial blood pressure and heart rate. Although glucagon caused a minimal effect and GLP-1-(1-37) produced a moderate increase of both systolic and diastolic blood pressure, GLP-1-(7-36) amide induced the greatest increases in both parameters. Systolic and diastolic blood pressure and heart rate values increased when doses of the peptides were increased. By contrast, GLP-2 did not modify either arterial blood pressure or heart rate values. To determine whether the effects of GLP-1-(7-36) amide were mediated through catecholamines, the rats were pretreated with reserpine, propranolol, or phentolamine before administration of the peptide. In these three experimental groups, GLP-1-(7-36) amide increases mean arterial blood pressure and heart rate to the same level or even greater than that observed in nonpretreated rats. These findings indicate that GLP-1-(7-36) amide significantly increases arterial blood pressure and heart rate and that these effects are not mediated through catecholamines.

Review article: the pathophysiology and pharmacological treatment of portal hypertension

The pathogenesis of portal hypertension remains poorly understood. Similarly, pharmacological manipulation for the prevention and treatment of variceal haemorrhage has not fulfilled the promise of the 1980s. This article reviews current concepts in the pathophysiology of portal hypertension and considers pharmacotherapy for the treatment of variceal bleeding.

Effects of glucagon on systemic and splanchnic circulation in conscious rats with biliary cirrhosis

To elucidate the relationship between the haemodynamic changes and glucagon in cirrhosis, we infused physiologic and supraphysiologic doses of this hormone in conscious rats with portal hypertension due to biliary cirrhosis. Cardiac output and splanchnic organ blood flows were measured by the radioactive microsphere method before and 30 min after glucagon infusion at doses of 2, 5 and 10 ng/min. Serum glucagon increased from a basal level of 92 +/- 17 pg/ml (mean +/- S.E.) to 399 +/- 89, 1151 +/- 136 and 2064 +/- 328 pg/ml, respectively, in sham-operated rats, and from 743 +/- 75 pg/ml to 1497 +/- 197, 1583 +/- 356 and 2957 +/- 649 pg/ml, respectively, in cirrhotic animals at 2, 5 and 10 ng/min doses. In both groups, cardiac output did not change after glucagon infusion at 2 and 5 ng/min doses, suggesting that factors other than glucagon are primarily responsible for the systemic hyperdynamic circulation in cirrhosis. Portal tributary blood flow increased significantly after glucagon infusion in sham-operated rats by 34 and 65% at doses of 5 ng/ml and 10 ng/ml, respectively, and in cirrhotic rats by 29% at a dose of 10 ng/ml. However, portal tributary blood flow did not change after glucagon infusion at the physiologic dose of 2 ng/min. This study shows that glucagon infused at a physiologic dose does not increase splanchnic blood flow, although it increases portal tributary blood flow at supraphysiologic doses. The discrepancy between blood glucagon levels and splanchnic haemodynamic responses suggests that glucagon plays only a minor role and that other factors are primarily responsible for the hyperdynamic state of the splanchnic circulation in rats with biliary cirrhosis.

Characterization of hepatic hemodynamics in cirrhotics and non-cirrhotics. Effect of glucagon infusion

The effect of glucagon on hepatic regional hemodynamics was investigated in patients with chronic liver disease during peritoneoscopy with reflectance spectrophotometry. When glucagon was infused intravenously in patients with a non-cirrhotic liver, the regional hepatic tissue oxygen consumption, as estimated spectrophotometrically, increased significantly, whereas the index of hepatic tissue blood volume did not change appreciably, and consequently, the oxygen saturation of hemoglobin in the hepatic tissue blood decreased. In contrast, the administration of glucagon in patients with liver cirrhosis resulted in a significant increase in the index of hepatic tissue blood volume and produced a minor increase in hepatic tissue oxygen consumption. The oxygen saturation of hepatic blood hemoglobin tended to increase in the cirrhotics. The result suggests the presence of functional vasoconstriction at the presinusoidal and/or sinusoidal vessels in the cirrhotic liver, possibly due to a decreased vasomotor activity and/or an abnormal regulatory function of vasoactive substances, which are released by glucagon.

Comparison of the effects of intravenous and intrasplenic infusions of glucagon on cardiac output and its distribution in the rat

In order to determine whether or not glucagon released from the pancreas might have local vascular effects, the actions upon regional haemodynamics in the anaesthetised rat of two doses of glucagon (2 and 10 micrograms kg-1 min-1) infused intrasplenically (and thus into the portal vein) were compared with those of a single dose (2 micrograms kg-1 min-1) infused i.v. Infusion of glucagon i.v. produced a significantly increased heart rate (by 6%) and cardiac output (by 23%) in the experimental animals compared to those receiving saline by the same route. Total peripheral resistance fell by 24%. A greater proportion of the cardiac output passed to the coronary and renal vascular beds and blood flow was increased in the spleen, testes, pectoral skeletal muscle, stomach and small intestine as well as the heart and kidneys. The lower dose infused intrasplenically had no significant effect on cardiac output or total peripheral resistance but significantly increased the proportion of cardiac output passing both to the stomach and the small intestine such that the percentage of cardiac output flowing through the portal vein increased from 19.1 +/- 1.1% to 23.8 +/- 1.7%. Intrasplenic infusion of 10 micrograms kg-1 min-1 significantly increased cardiac output (by 29%) but reduced total peripheral resistance by 37%. Greater fractions of the cardiac output were received by the spleen, small intestine and epididymides. Blood flow was increased in these organs and the skin, kidneys, stomach, large intestine and the mesentery. It is concluded that pharmacologically effective amounts of glucagon only passed into the systemic circulation with the higher dose infused intrasplenically.(ABSTRACT TRUNCATED AT 250 WORDS)

Responses of isolated dog blood vessels to glucagon

The responses to glucagon were compared in helical strips of different arteries or veins isolated from dogs, and the relationship between the glucagon-induced relaxation and the intracellular cyclic AMP content in the arteries was studied. Relaxations induced by glucagon followed the order renal greater than mesenteric greater than femoral greater than cerebral = coronary arteries precontracted with PGF2 alpha. Glucagon-induced relaxations were greater in renal and mesenteric arteries than in the respective veins. Removal of the endothelium from the renal artery did not alter the magnitude of relaxations induced by glucagon nor the apparent ED50 value of glucagon. Glucagon increased the intracellular cyclic AMP content in both renal and coronary arteries, but the nucleotide increments were significantly greater in renal arteries than in coronary arteries. Isoproterenol produced significant increases in the intracellular cyclic AMP content and relaxations in renal and coronary arteries. Relaxations induced by dibutyryl cyclic AMP were greater in coronary arteries than in renal arteries. It is concluded that glucagon relaxed differently a variety of dog blood vessels, possibly by different extents of production of cellular cyclic AMP. The quantity and sensitivity of receptors for glucagon in smooth muscle cells may be heterogeneous in the vessels.

Effects of gastrointestinal hormones on transport by peritoneal dialysis

Because the gastrointestinal hormones are known to dilate the splanchnic vasculature, their effects on transport of water and solutes during peritoneal dialysis were studied in an experimental model, the rabbit. In unanesthetized rabbits, dialysate volume was calculated by isotope dilution, and clearances were estimated by dialysate/plasma concentration ratio factored by minute volume. With isotonic dialysis solution, the mean increment in dialysate volume per minute of intraperitoneal dwell was 0.19 ml/kg/min, and mean clearances of creatinine and urea were 0.71 and 0.90 ml/kg/min, respectively. When administered intravenously, secretin significantly augmented osmotically induced water flux, but not when given intraperitoneally. Neither glucagon nor cholecystokinin affected dialysate volume. Intravenously, but not intraperitoneally, glucagon increased peritoneal clearances of creatinine and urea to more than 150% of control values. Neither cholecystokinin nor secretin augmented significantly peritoneal mass transport when given by either route. The data suggest that the site of acton is the endothelial surface of the membrane, that the mechanisms of augmenting transport involve increased permeability and/or surface area, and that agents which combine an increase in mass transport and capillary filtration coefficient may be clinically useful.

Urinary sodium and calcium in various dog models and relationship to endogenous plasma glucagon

Clearance studies were performed in 23 dogs undergoing extracellular volume (ECV) expansion by saline in order to evaluate relationship between endogenous glucagon and renal excretion of sodium and calcium. In control animals plasma glucagon (pG1) rose following 120 minutes of ECV expansion and was further increased by additional infusion of arginine. In pancreatectomised dogs ECV expansion failed to increase pG1. Both fractional and absolute urinary excretion of sodium in pancreatectomised dogs were markedly lower compared to control dogs. The difference in renal sodium excretion between control and pancreatectomised animals cannot be explained by the sum of nonhormonal factors influencing sodium excretion. In thyro-parathyroidectomised dogs renal sodium excretion was lower than in control dogs, but significantly higher than in pancreatectomised dogs. The arginine-induced increase of glucagon was associated with an increase of renal sodium and calcium excretion in each group under study without any change in glomerular filtration rate. In control dogs all parameters of renal sodium and calcium excretion investigated in this study were linearly correlated. Thyro-parathyroidectomy did not influence the relationship between renal sodium and calcium excretion. Hyperglucagonaemia therefore might be one factor contributing to the hypercalciuria associated with renal stone formation. In pancreatectomised dogs undergoing ECV expansion there was no significant correlation between renal sodium and calcium excretion. Pancreatic hormones might be involved in the coupling of renal sodium and calcium excretion.

A conrolled trial of glucagon in experimental pancreatitis

This study was designed to assess the value of glucagon infusion in pigs with experimental pancreatitis. The condition was induced by injection of bile into the pancreatic duct directly after intravenous injection of secretion. Macroscopic haemorrpagic pancreatitis ensued immediately, and was accompanied by a rise in the serum amylase of five to ten times. An experimental group of 15 pigs was given glucagon by continous infusion for 18 hours beginning 18 hours after induction of pancreatitis. A control group was given intravenous saline. Fourteen of the 15 treated animals survived for 1 week and 3 died within 2 weeks, after which the remaining animals were sacrificed. Ten of the 15 controls died within the first week. Serum amylase levels in both groups began to decline when infusion was commenced, but levels in the treated group were significantly lower than in the controls. Autopsy showed prominent peripancreatic granulation tissue in the treated animals, a significant incidence of pericarditis in both groups and pancreatic pseudocysts in 3 controls and 1 treated animal. These results suggest that glucagon effectively reduced the mortality in pigs with experimental pancreatitis and that a controlled clinical trial of treatment is justified.

A comparison of the hemodynamic effects of inotropic agents

This experimental study was conducted to compare and contrast the cardiovascular effects of the drugs most commonly used to alleviate low-cardiac-output syndrome. Twenty-five adult mongrel dogs were infused with sodium pentobarbital (60 mg/min) until their cardiac output fell to 50+/-5% of the average control values determined by thermodilution technique prior to pentobarbital infusion. The dogs were then divided into six groups, and one of the following agents or combinations of agents was administered to each group: isoproterenol, glucagon, dopamine, dobutamine, levarterenol and phentolamine, or levarterenol and nitroprusside. All drugs, except for glucagon and the combination of levarterenol and nitroprusside, produced an increase in cardiac output above the nonfailure baseline values. However, this increase was accompanied by an undesirable, pronounced tachycardia except when levarterenol was used simultaneously with phentolamine. Both dopamine and the combined infusion of levarterenol and phentolamine proved the most effective in restoring systemic arterial pressure to near baseline values, and both were able to increase renal blood flow above the failure baseline values. While renal blood flow remained elevated with all dosages of levarterenol and phentolamine, it tended to decrease with larger doses of dopamine. These experiments demonstrate that there are major advantages in the use of simultaneously infused levarterenol and phentolamine for control of low-cardiac-output syndrome: increased cardiac output without elevated peripheral vascular resistance, restoration of systemic arterial pressure and consequent improved coronary flow, absence of tachycardia, and augmented renal blood flow.

The inhibition by glucagon of the vasoconstrictor actions of noradrenaline, angiotensin and vasopressin on the hepatic arterial vascular bed of the dog

1 The hepatic artery of the anaesthetized dog was cannulated and perfused from a femoral artery, the blood flow and perfusion pressure being monitored continuously. The sympathetic periarterial nerves were divided. 2 Dose-dependent increases in hepatic arterial vascular resistance (HAVR) resulted from intra-arterial injections of noradrenaline, angiotensin and vasopressin. 3 Single injections of glucagon (100 mug, i.a.) caused a transient significant fall in HAVR of 19.9 +/- 3.2%, and infusions of 25 mug/min of glucagon intra-arterially caused maintained reductions in HAVR of 16.9 +/- 4.2%. 4 After single injections of 100 mug glucagon intra-arterially the vasoconstrictor responses to noradrenaline, angiotensin, and vasopressin were reduced by about 85-95%. Recovery occurred in 8-10 minutes. 5 Intra-arterial infusions of glucagon, 2.5-50.0 mug/min, reduced the effects of test doses of noradrenaline, angiotensin and vasopressin throughout the period of the infusions. 6 Dose-response curves to the constrictor agents were constructed before, during and after intra-arterial infusions of 25 mug/min of glucagon. Glucagon caused a parallel shift of the curves for noradrenaline and angiotensin to the right, with no suppression of the maximum response. 7 Infusions of glucagon shifted the dose-response curve for vasopressin to the right, but, in contrast to noradrenaline and angiotensin, the shift was nonparallel and there was a suppression of the maximum response by about one-half. 8 A large dose of insulin, 10 iu, transiently reduced HAVR and caused a weak and very transient inhibition of the effect of test doses of noradrenaline. The characteristics of these effects were quite different from those of glucagon. 9 It is possible that the antagonism by glucagon of the vasoconstrictor responses of the hepatic arterial vasculature may be important in protecting this vascular bed from the effects of concomitantly released vasoconstrictor agents.

Neonatal small left colon syndrome: intramural not intraluminal obstruction

We have described a characteristic syndrome of intestinal dysfunction in infants of diabetic mothers. This finding appears to result from a transient intramural dysfunction. Many respond to rectal irrigations alone. However, a significant number will require close observation and possible diversion for persistent partial intestinal obstruction. Failure to recognize persistent obstruction may result in intestinal perforation.

Endocrine tumour in kidney affecting small bowel structure, motility, and absorptive function

A 44-year-old woman is described with an endocrine tumour arising in the kidney. There were associated abnormalities of small intestinal morphology, motility, and absorptive function. These abnormalities reversed on removal of the tumour. Detailed studies showed that the tumour contained, and was secreting, glucagon. It is postulated that the intestinal abnormalities may have resulted from glucagon itself or another, as yet unidentified, hormone.

Glucagon in prevention and abolition of ouabain-induced ventricular tachycardia in normokalemic and hypokalemic dogs

A recent study suggested that glucagon has antiarrhythmic properties in addition to its positive inotropic effect. The present study was designed to evaluate the efficacy of glucagon in preventing and converting ouabain-induced ventricular tachycardia (VT) in normokalemic and hypokalemic dogs. Paired studies were made in ten normokalemic dogs and in eight dogs rendered hypokalemic by diet and hydrochlorothiazide. All dogs were pretreated with glucagon, and the amount of ouabain required to produce VT was measured. Each dog served as its own control in a second study in which normal saline was substituted for glucagon. When VT was produced during the control study, the response to a bolus injection of glucagon was evaluated. (1) Pretreatment with glucagon delayed the appearance of VT in hypokalemic dogs but not in normokalemic dogs. (2) Glucagon, by bolus injection, converted VT to sinus rhythm in 78% of the normokalemic dogs and in 100% of the hypokalemic dogs. (3) The mechanisms by which glucagon exerts its antiarrhythmic effect are not clearly defined.