The contribution of endogenous insulin secretion to the ketogenic response to glucagon in man

Sustained effect of zinc-protamin-glucagon in hyperlipidaemic patients

Is is well known from laboratory investigations and acute intervention studies that glucagon is involved in lipid metabolism. The present study was undertaken in order to evaluate a possible sustained effect of zinc-protamin-glucagon in moderately hyperlipidaemic patients. 4 patients were investigated after an acute bolus dose of glucagon 5 mg intravenously and 16 patients were given zinc-protamin-glucagon 5 mg subcutaneously, b.i.d. for 5 days. A similar degree of decrease of plasma cholesterol and triglycerides was obtained in the acute and chronic study, while the increase in fasting blood sugar and plasma insulin seen in the acute study was not present after 5 days treatment. The effect on plasma triglycerides was much more variable than the effect on plasma cholesterol. Five days after treatment the lipid concentrations had returned to the pretreatment values. The effect could not be predicted from the pretreatment lipid concentrations, neither by the type of hyperlipidaemia present. The decrease in plasma cholesterol and triglycerides were not correlated. The drug might prove useful in the long term research of lipid metabolism and the various complex hormonal interactions.

Metabolic interactions of glucagon and cortisol in man--studies with somatostatin

The metabolic response to pathophysiologic concentrations of glucagon, induced by glucagon infusion, has been examined in normal man before and after 36-60 hr hypercortisolaemia, induced by administration of tetracosactrin-depot. Glucagon alone increased serum insulin levels twofold but blood glucose was unaltered. Plasma NEFA and blood ketone body concentrations were decreased by glucagon infusion. Tetracosactrin produced a threefold rise in serum cortisol levels and caused mild fasting hyperglycemia and hyperinsulinaemia. Subsequent glucagon infusion had no effect on circulating insulin, glucose, NEFA or ketone body concentrations. Simultaneous infusion of somatostatin, to produce partial insulin-deficiency, unmasked a hyperglycemic action of glucagon (+ 3.8 +/- 0.2 mmol/l at 90 min, p less than 0.02). This glucagon-induced rise in blood glucose was diminished by prior tetracosactrin administration. Tetracosactrin revealed a mild lipolytic action of glucagon in partial insulin deficiency, not apparent in the euadrenal state. Glucagon was equally hyperketonemic during somatostatin infusion before and after tetracosactrin. Thus the hyperglycemic and hyperketonemic actions of glucagon at pathophysiologic levels are restricted to insulin deficiency. Hypercortisolaemia reveals a lipolytic action of glucagon in insulin-deficient man but does not potentiate the hyperglycemic or hyperketonemic effects.

The acute metabolic effects of glucagon and its interactions with insulin in forearm tissue

The acute effects of glucagon (mol. wt. 3500) and its interactions with insulin were studied in the forearm during eight studies in seven normal, post-absorptive males. The protocol consisted of a 2 h baseline, 1 h glucagon perfusion (mean glucagon increment, 691 +/- 50 pg/ml), 1 h perfusion of both insulin and glucagon (mean insulin increment of 105 insulin and glucagon (mean insulin increment of 105 /- 13 mU/l) and a 30 min recovery period. Simultaneous arterial (A), deep venous (DV), and superficial venous (SV) blood samples were obtained at 30 min intervals. Perfusion of glucagon resulted in a decrease in (A-DV) non-esterified fatty acids of -0.128 +/- 0.057 mmol/l (n = 7, p less than 0.05) and (A-SV) non-esterified fatty acids of -0.081 +/- 0.36 mol/l (n = 7, p less than 0.05), as well as a change in deep compartment uptake of glycerol after 60 min of -0.044 +/- 0.019 mumol/min/100 ml of forearm tissue (n=6, p less than 0.05), indicating increased lipolysis. There was also a decrease in net glucose uptake as reflected by a change in (A-Dids of -0.081 +/- 0.36 mol/l (n = 7, p less than 0.05), as well as a change in deep compartment uptake of glycerol after 60 min of -0.044 +/- 0.019 mumol/min/100 ml of forearm tissue (n=6, p less than 0.05), indicating increased lipolysis. There was also a decrease in net glucose uptake as reflected by a change in (A-Dids of -0.081 +/- 0.36 mol/l (n = 7, p less than 0.05), as well as a change in deep compartment uptake of glycerol after 60 min of -0.044 +/- 0.019 mumol/min/100 ml of forearm tissue (n=6, p less than 0.05), indicating increased lipolysis. There was also a decrease in net glucose uptake as reflected by a change in (A-DV) of -0.24 +/- 0.09 mmol/l (n = 7, p less than 0.025) and (A-SV) of 0.10 +/- 0.05 mmol/l (n = 7, p less than 0.05). There was also a net decrease in deep arteriovenous differences of potassium in six of seven subjects. Insulin levels, similar to those found after a meal, rapidly reversed the effects of glucagon on non-esterified fatty acid, glucose and potassium. These effects persisted throughout the recovery period.

Acute hormonal effects on carnitine metabolism in thin and obese subjects: responses to somatostatin, glucagon, and insulin

Plasma free carnitine and acylcarnitines were determined in man during acutely induced insulin deficiency. A 5-hr infusion of somatostatin at 6 microgram/min in 10 thin subjects produced profound, sustained hypoinsulinemia and led to rapid increases in plasma free fatty acids and ketoacids (peak increments of 0.67 mM each). Simultaneously, plasma free carnitine decreased, while plasma long-chain and short-chain acylcarnitines increased significantly. When hyperglucagonemia was created by inclusion of glucagon with the somatostatin, the hyperketonemia was reversed after 2 hr and the increase in acylcarnitine abolished. However, the decrease in free carnitine was accentuated. The antiketogenic effect of adding glucagon was due to an eventual breakthrough of the somatostatin blockade on insulin secretion, the latter gradually returning toward preinfusion levels. Inclusion of exogenous insulin with the somatostatin-glucagon infusion immediately lowered free fatty acids and ketoacids. Acylcarnitines also declined promptly, while the accelerated fall in free carnitine produced by glucagon was blunted by the addition of insulin. Qualitatively and quantitatively comparable results were seen in seven obese subjects. This study suggests: (1) the increase in plasma acylcarnitines previously described in fasting and diabetic ketosis is largely due to insulin deficiency; (2) the corresponding decrease in plasma free carnitine is attributable both to insulin deficiency and glucagon excess; and (3) the resistance of obese subjects to ketosis is unlikely to be due to deficits in carnitine or carnitine acyltransferases.

The role of glucagon in the regulation of plasma lipids

The role of glucagon in regulating plasma lipid concentrations (nonesterified fatty acids, ketone bodies, and triglycerides) is reviewed. The effects of glucagon-induced insulin secretion upon this lipid regulation are discussed that may resolve conflicting reports in the literature are resolved. In addition, the unresolved problem concerning the pharmacologic versus physiologic effects of glucagon is stressed. Glucagon's role in stimulating lipolysis at the adipocyte serves two important functions. First, it provides plasma nonesterified fatty acids for energy metabolism and secondly, it ensures substrate for hepatic ketogenesis. In vitro, glucagon's lipolytic activity has been consistently observed, but in vivo, this activity has sometimes been obscured by the effects of glucagon-induced insulin secretion. Frequently, a biphasic response has been reported in which a direct lipolytic response is followed by a glucagon-induced insulin suppression of plasma nonesterified fatty acid concentration. When the glucagon-induced insulin secretion has been controlled by various in vivo techniques, glucagon's lipolytic activity in vivo has frequently been demonstrable. In the 1960s, in vitro liver perfusion experiments demonstrated that glucagon enhanced hepatic ketogenesis independent of glucagon's lipolytic activity. However, this direct effect of glucagon on the hepatocyte was not universally accepted because of conflicting reports in the literature. Failure to observe an in vitro ketogenic effect of the hormone in some studies may have been due to suboptimal experimental conditions. Certain factors are now known to influence the ketogenic response, such as the concentration of fatty acids in the media and the nutritional status of the animal. Under optimal in vitro conditions with liver preparations from fed animals, the ketogenic response to physiologic concentrations of glucagon has been demonstrated. However, further study is necessary to define the quantitative ketogenic role of the hormone. In spite of this early in vitro work, glucagon was not definitely shown to be ketogenic in vivo (independent of fatty acid availability) both in the rat and in diabetic man until 1975. Since these observations, several reports have confirmed the ketogenic action of glucagon in vivo by direct hepatic catheterization experiments. Glucagon's role in decreasing hepatic triglyceride synthesis and secretion in vitro has been repeatedly shown but the mechanism is unresolved. This lipid regulatory action of glucagon has been more difficult to demonstrate in vivo because of the many variables that affect triglyceride synthesis. Under specific experimental conditions, however, glucagon has been shown to decrease plasma triglyceride concentration in man at both physiologic and pharmacologic concentrations. Hepatic catheterization experiments have also confirmed this effect in man. The regulation of lipids by glucagon fits well into its role as a stress hormone...

Metabolic effects of glucagon in endogenous hypertriglyceridemia

The metabolic effects of glucagon, administered i.v. in doses of 1 microgram/kg, were evaluated in two groups of patients with endogenous hypertriglyceridemia (Types IV and V according to Fredrickson) with normal and reduced glucose tolerance and in a control group. Glucagon had a lipolytic effect, evaluated as the plasma increase of free fatty acids (FFA) during the first 20 min in normal subjects, but not in the two hyperlipemic groups. A negative correlation was observed between fasting IRI level and FFA mobilization. The ketogenic and hypotriglyceridemic effects of glucagon were demonstrated in normal and hyperlipemic groups. It would seem, therefore, that at the pharmacological doses injected, there is no resistance to the hypotriglyceridemic effect of glucagon in endogenous hypertriglyceridemia.

Hormonal and metabolic responses to glucagon in diabetes mellitus

The metabolic and hormonal responses to glucagon (1 mg, subcutaneous) were studied in twelve diabetic and twelve non-diabetic subjects. Diabetics showed a GH response, which although commencing slightly earlier, did not otherwise differ from that of the controls. There was the expected diminished insulin response to glucagon among the patients on oral agents. The GH response to glucagon in the diabetics began before there was any significant fall in blood glucose (BG). The hyperglycaemic response in the diabetics peaked later, was greater in amplitude and was more prolonged. In this group both pyruvate and lactate changes were delayed and diminished in amplitude. The diabetics showed a biphasic response of both acetoacetate and 3-hydroxybutyrate to glucagon; a small transient significant rise in the first 2 h followed by a second rise after 3h. In contrast the controls showed a significant fall in these metabolites during the initial 2 h, before a rise after 3 h. The significance of these hormonal and metabolic responses is discussed.