Impaired responsiveness to the effect of glucagon on plasma adenosine 3':5'-cyclic monophosphate in normal man

Association between Cardiovascular Disease and Liver Disease, from a Clinically Pragmatic Perspective as a Cardiologist

Cardiovascular diseases and liver diseases are closely related. Non-alcoholic fatty liver disease has the same risk factors as those for atherosclerotic cardiovascular disease and may also be a risk factor for atherosclerotic cardiovascular disease on its own. Heart failure causes liver fibrosis, and liver fibrosis results in worsened cardiac preload and congestion. Although some previous reports regard the association between cardiovascular diseases and liver disease, the management strategy for liver disease in patients with cardiovascular diseases is not still established. This review summarized the association between cardiovascular diseases and liver disease. In patients with non-alcoholic fatty liver disease, the degree of liver fibrosis progresses with worsening cardiovascular prognosis. In patients with heart failure, liver fibrosis could be a prognostic marker. Liver stiffness assessed with shear wave elastography, the fibrosis-4 index, and non-alcoholic fatty liver disease fibrosis score is associated with both liver fibrosis in patients with liver diseases and worse prognosis in patients with heart failure. With the current population ageing, the importance of management for cardiovascular diseases and liver disease has been increasing. However, whether management and interventions for liver disease improve the prognosis of cardiovascular diseases has not been fully understood. Future investigations are needed.

High-Dose Glucagon Has Hemodynamic Effects Regardless of Cardiac Beta-Adrenoceptor Blockade: A Randomized Clinical Trial

Background Intravenous high-dose glucagon is a recommended antidote against beta-blocker poisonings, but clinical effects are unclear. We therefore investigated hemodynamic effects and safety of high-dose glucagon with and without concomitant beta-blockade. Methods and Results In a randomized crossover study, 10 healthy men received combinations of esmolol (1.25 mg/kg bolus+0.75 mg/kg/min infusion), glucagon (50 µg/kg), and identical volumes of saline placebo on 5 separate days in random order (saline+saline; esmolol+saline; esmolol+glucagon bolus; saline+glucagon infusion; saline+glucagon bolus). On individual days, esmolol/saline was infused from -15 to 30 minutes. Glucagon/saline was administered from 0 minutes as a 2-minute intravenous bolus or as a 30-minute infusion (same total glucagon dose). End points were hemodynamic and adverse effects of glucagon compared with saline. Compared with saline, glucagon bolus increased mean heart rate by 13.0 beats per minute (95% CI, 8.0-18.0; P<0.001), systolic blood pressure by 15.6 mm Hg (95% CI, 8.0-23.2; P=0.002), diastolic blood pressure by 9.4 mm Hg (95% CI, 6.3-12.6; P<0.001), and cardiac output by 18.0 % (95% CI, 9.7-26.9; P=0.003) at the 5-minute time point on days without beta-blockade. Similar effects of glucagon bolus occurred on days with beta-blockade and between 15 and 30 minutes during infusion. Hemodynamic effects of glucagon thus reflected pharmacologic glucagon plasma concentrations. Glucagon-induced nausea occurred in 80% of participants despite ondansetron pretreatment. Conclusions High-dose glucagon boluses had significant hemodynamic effects regardless of beta-blockade. A glucagon infusion had comparable and apparently longer-lasting effects compared with bolus, indicating that infusion may be preferable to bolus injections. Registration Information URL: https://www.clinicaltrials.gov; Unique identifier: NCT03533179.

Glucagon revisited: Coordinated actions on the liver and kidney

Glucagon secretion is stimulated by a low plasma glucose concentration. By activating glycogenolysis and gluconeogenesis in the liver, glucagon contributes to maintain a normal glycemia. Glucagon secretion is also stimulated by the intake of proteins, and glucagon contributes to amino acid metabolism and nitrogen excretion. Amino acids are used for gluconeogenesis and ureagenesis, two metabolic pathways that are closely associated. Intriguingly, cyclic AMP, the second messenger of glucagon action in the liver, is released into the bloodstream becoming an extracellular messenger. These effects depend not only on glucagon itself but on the actual glucagon/insulin ratio because insulin counteracts glucagon action on the liver. This review revisits the role of glucagon in nitrogen metabolism and in disposal of nitrogen wastes. This role involves coordinated actions of glucagon on the liver and kidney. Glucagon influences the transport of fluid and solutes in the distal tubule and collecting duct, and extracellular cAMP influences proximal tubule reabsorption. These combined effects increase the fractional excretion of urea, sodium, potassium and phosphates. Moreover, the simultaneous actions of glucagon and extracellular cAMP are responsible, at least in part, for the protein-induced rise in glomerular filtration rate that contributes to a more efficient excretion of protein-derived end products.

Glucagon actions on the kidney revisited: possible role in potassium homeostasis

It is now recognized that the metabolic disorders observed in diabetes are not, or not only due to the lack of insulin or insulin resistance, but also to elevated glucagon secretion. Accordingly, selective glucagon receptor antagonists are now proposed as a novel strategy for the treatment of diabetes. However, besides its metabolic actions, glucagon also influences kidney function. The glucagon receptor is expressed in the thick ascending limb, distal tubule, and collecting duct, and glucagon regulates the transepithelial transport of several solutes in these nephron segments. Moreover, it also influences solute transport in the proximal tubule, possibly by an indirect mechanism. This review summarizes the knowledge accumulated over the last 30 years about the influence of glucagon on the renal handling of electrolytes and urea. It also describes a possible novel role of glucagon in the short-term regulation of potassium homeostasis. Several original findings suggest that pancreatic α-cells may express a “potassium sensor” sensitive to changes in plasma K concentration and could respond by adapting glucagon secretion that, in turn, would regulate urinary K excretion. By their combined actions, glucagon and insulin, working in a combinatory mode, could ensure an independent regulation of both plasma glucose and plasma K concentrations. The results and hypotheses reviewed here suggest that the use of glucagon receptor antagonists for the treatment of diabetes should take into account their potential consequences on electrolyte handling by the kidney.

Protein- and diabetes-induced glomerular hyperfiltration: role of glucagon, vasopressin, and urea

A single protein-rich meal (or an infusion of amino acids) is known to increase the glomerular filtration rate (GFR) for a few hours, a phenomenon known as “hyperfiltration.” It is important to understand the factors that initiate this upregulation because it becomes maladaptive in the long term. Several mediators and paracrine factors have been shown to participate in this upregulation, but they are not directly triggered by protein intake. Here, we explain how a rise in glucagon and in vasopressin secretion, directly induced by protein ingestion, might be the initial factors triggering the hepatic and renal events leading to an increase in the GFR. Their effects include metabolic actions in the liver and stimulation of sodium chloride reabsorption in the thick ascending limb. Glucagon is not only a glucoregulatory hormone. It is also important for the excretion of nitrogen end products by stimulating both urea synthesis in the liver (along with gluconeogenesis from amino acids) and urea excretion by the kidney. Vasopressin allows the concentration of nitrogenous end products (urea, ammonia, etc.) and other protein-associated wastes in a hyperosmotic urine, thus allowing a very significant water economy characteristic of all terrestrial mammals. No hyperfiltration occurs in the absence of one or the other hormone. Experimental results suggest that the combined actions of these two hormones, along with the complex intrarenal handling of urea, lead to alter the composition of the tubular fluid at the macula densa and to reduce the intensity of the signal activating the tubuloglomerular feedback control of GFR, thus allowing GFR to raise. Altogether, glucagon, vasopressin, and urea contribute to set up the best compromise between efficient urea excretion and water economy.

Abdominal contributions to cardiorenal dysfunction in congestive heart failure

Current pathophysiological models of congestive heart failure unsatisfactorily explain the detrimental link between congestion and cardiorenal function. Abdominal congestion (i.e., splanchnic venous and interstitial congestion) manifests in a substantial number of patients with advanced congestive heart failure, yet is poorly defined. Compromised capacitance function of the splanchnic vasculature and deficient abdominal lymph flow resulting in interstitial edema might both be implied in the occurrence of increased cardiac filling pressures and renal dysfunction. Indeed, increased intra-abdominal pressure, as an extreme marker of abdominal congestion, is correlated with renal dysfunction in advanced congestive heart failure. Intriguing findings provide preliminary evidence that alterations in the liver and spleen contribute to systemic congestion in heart failure. Finally, gut-derived hormones might influence sodium homeostasis, whereas entrance of bowel toxins into the circulatory system, as a result of impaired intestinal barrier function secondary to congestion, might further depress cardiac as well as renal function. Those toxins are mainly produced by micro-organisms in the gut lumen, with presumably important alterations in advanced heart failure, especially when renal function is depressed. Therefore, in this state-of-the-art review, we explore the crosstalk between the abdomen, heart, and kidneys in congestive heart failure. This might offer new diagnostic opportunities as well as treatment strategies to achieve decongestion in heart failure, especially when abdominal congestion is present. Among those currently under investigation are paracentesis, ultrafiltration, peritoneal dialysis, oral sodium binders, vasodilator therapy, renal sympathetic denervation and agents targeting the gut microbiota.

The extracellular cAMP-adenosine pathway regulates expression of renal D1 dopamine receptors in diabetic rats

Activation of D1 dopamine receptors expressed in the kidneys promotes the excretion of sodium and regulates sodium levels during increases in dietary sodium intake. A decrease in the expression or function of D1 receptors results in increased sodium retention which can potentially lead to the development of hypertension. Studies have shown that in the absence of functional D1 receptors, in null mice, the systolic, diastolic, and mean arterial pressures are higher. Previous studies have shown that the expression and function of D1 receptors in the kidneys are decreased in animal models of diabetes. The mechanisms that down-regulate the expression of renal D1 receptor gene in diabetes are not well understood. Using primary renal cells and acutely isolated kidneys from the streptozotocin-induced rat diabetic model, we demonstrate that the renal D1 receptor expression is down-regulated by the extracellular cAMP-adenosine pathway in vitro and in vivo. In cultures of primary renal cells, a 3 mm, 60-h cAMP treatment down-regulated the expression of D1 receptors. In vivo, we determined that the plasma and urine cAMP levels as well as the expression of 5'-ectonucleotidase, tissue-nonspecific alkaline phosphatase, and adenosine A2a receptors are significantly increased in diabetic rats. Inhibitors of 5'-ectonucleotidase and tissue-nonspecific alkaline phosphatase, α,β-methyleneadenosine 5'-diphosphate, and levamisole, respectively, blocked the down-regulation of D1 receptors in the primary renal cells and in the kidney of diabetic animals. The results suggest that inhibitors of the extracellular cAMP-adenosine pathway reverse the down-regulation of renal D1 receptor in diabetes.

Extracellular calcium and cAMP: second messengers as "third messengers"?

Calcium and cyclic AMP are familiar second messengers that typically become elevated inside cells on activation of cell surface receptors. This article will explore emerging evidence that transport of these signaling molecules across the plasma membrane allows them to be recycled as "third messengers," extending their ability to convey information in a domain outside the cell.

Extracellular cAMP inhibits proximal reabsorption: are plasma membrane cAMP receptors involved?

Glucagon binding to hepatocytes has been known for a long time to not only stimulate intracellular cAMP accumulation but also, intriguingly, induce a significant release of liver-borne cAMP in the blood. Recent experiments have shown that the well-documented but ill-understood natriuretic and phosphaturic actions of glucagon are actually mediated by this extracellular cAMP, which inhibits the reabsorption of sodium and phosphate in the renal proximal tubule. The existence of this "pancreato-hepatorenal cascade" indicates that proximal tubular reabsorption is permanently influenced by extracellular cAMP, the concentration of which is most probably largely dependent on the insulin-to-glucagon ratio. The possibility that renal cAMP receptors may be involved in this process is supported by the fact that cAMP has been shown to bind to brush-border membrane vesicles. In other cell types (i.e., adipocytes, erythrocytes, glial cells, cardiomyocytes), cAMP eggress and/or cAMP binding have also been shown to occur, suggesting additional paracrine effects of this nucleotide. Although not yet identified in mammals, cAMP receptors (cARs) are already well characterized in lower eukaryotes. The amoeba Dictyostelium discoideum expresses four different cARs during its development into a multicellular organism. cARs belong to the superfamily of seven transmembrane domain G protein-coupled receptors and exhibit a modest homology with the secretin receptor family (which includes PTH receptors). However, the existence of specific cAMP receptors in mammals remains to be demonstrated. Disturbances in the pancreato-hepatorenal cascade provide an adequate pathophysiological understanding of several unexplained observations, including the association of hyperinsulinemia and hypertension, the hepatorenal syndrome, and the hyperfiltration of diabetes mellitus. The observations reviewed in this paper show that cAMP should no longer be regarded only as an intracellular second messenger but also as a first messenger responsible for coordinated hepatorenal functions, and possibly for paracrine regulations in several other tissues.

Cyclic AMP is a hepatorenal link influencing natriuresis and contributing to glucagon-induced hyperfiltration in rats

The effects of glucagon (G) on proximal tubule reabsorption (PTR) and GFR seem to depend on a prior action of this hormone on the liver resulting in the liberation of a mediator and/or of a compound derived from amino acid metabolism. This study investigates in anesthetized rats the possible contribution of cAMP and urea, alone and in combination with a low dose of G, on phosphate excretion (known to depend mostly on PTR) and GFR. After a 60-min control period, cAMP (5 nmol/min x 100 grams of body weight [BW]) or urea (2.5 micromol/min x 100 grams BW) was infused intravenously for 200 min with or without G (1.2 ng/min x 100 grams BW, a physiological dose which, alone, does not influence PTR or GFR). cAMP increased markedly the excretion of phosphate and sodium (+303 and +221%, respectively, P < 0.01 for each) but did not alter GFR. Coinfusion of cAMP and G induced the same tubular effects but also induced a 20% rise in GFR (P < 0.05). Infusion of urea, with or without G, did not induce significant effects on PTR or GFR. After G infusion at increasing doses, the increase in fractional excretion of phosphate was correlated with a simultaneous rise in plasma cAMP concentration and reached a maximum for doubling of plasma cAMP. These results suggest that cAMP, normally released by the liver into the blood under the action of G, (a) is probably an essential hepatorenal link regulating the intensity of PTR, and (b) contributes, in conjunction with specific effects of G on the nephron, to the regulation of GFR.

An investigation of the biological activity of parathyroid hormone in pseudohypoparathyroidism: comparison with vitamin D deficiency

Circulating parathyroid hormone was studied in patients with pseudohypoparathyroidism and compared with that in normal subjects and patients with hypocalcaemia due to postsurgical or idiopathic hypoparathyroidism or vitamin D deficiency. The cytochemical bioassay was used to measure bioactivity and an amino-terminal specific immunoradiometric assay was used to measure immunoreactivity. In normal subjects (n = 12) the concentration of bioactive parathyroid hormone was 1.1-5.9 pg/ml. It was higher in patients with newly diagnosed, untreated pseudohypoparathyroidism (n = 4, range 20-53 pg/ml) and similarly raised in patients with untreated vitamin D deficiency (n = 9, range 23-74 pg/ml). The degree of hypocalcaemia was similar in these two groups of patients. By contrast, the concentration of bioactive parathyroid hormone was low (less than 0.6 pg/ml) in four patients with untreated postsurgical or idiopathic hypoparathyroidism. Restoration of normocalcaemia reduced the concentrations of bioactive PTH in both pseudohypoparathyroidism and vitamin D deficiency. Thus, in this respect the parathyroid glands in both conditions appeared to respond to the circulating calcium concentration. Immunoreactive PTH was also raised in patients with untreated pseudo-hypoparathyroidism and vitamin D deficiency, but restoration of normocalcaemia did not always reduce immunoreactive PTH to normal in these patients. Thus, there can be dissociation between bioactivity and immunoreactivity even when the PTH is measured in an amino-terminal specific assay.

Anomalous plasma cyclic AMP responses to glucagon in patients with liver disease

The purpose of the present study is to show anomalies of the plasma cAMP response of patients with hepatic disorders to a single injection of a low dose of glucagon (1 microgram/kg body wt). The response was markedly blunted in patients with liver cirrhosis and potentiated in patients with acute or chronic hepatitis. This glucagon test is, therefore, promising for development as a simple diagnostic means without undertaking liver biopsy to distinguish cirrhosis from chronic hepatitis.