Influence of physiologic hyperglucagonemia on basal and insulin-inhibited splanchnic glucose output in normal man

Effect of intermittent physiologic hyperglucagonemia on postprandial plasma glucose levels in normal man

The ability of glucagon to impair glucose tolerance has been questioned by studies involving infusion of exogenous glucagon during a glucose load. Since such hormone administration may not reflect the physiologic pattern of glucagon secretion and may result in hepatic downregulation to glucagon, the present experiments have examined the effects of intermittent endogenous hyperglucagonemia (induced by episodic infusion or arginine) on plasma glucose profiles of normal man following ingestion of mixed meals. In control studies following meal ingestion, plasma glucose, insulin and glucagon increased respectively 15-30 mg/dl, 30-60 uU/ml and 25-50 pg/ml. When meals were accompanied by arginine infusions, plasma glucagon responses were augmented three to fourfold (p less than 0.05). Amplitudes of glycemic excursions during infusion of arginine (345 +/- 40 mg/dl) were significantly augmented compared to those observed in control studies (286 +/- 34 mg/dl, p less than 0.02). These results indicate that intermittent increases in plasma glucagon within the physiologic range can adversely affect postprandial glucose profiles in normal man despite concomitant hyperinsulinemia and suggest that such hyperglucagonemia may contribute to impaired postprandial glucose tolerance in diabetic individuals in whom insulin secretion is deficient.

The metabolic effects of chronic hyperglucagonaemia

A subject with a benign glucagonoma was studied before and after complete resection of his pancreatic tumour. Studies were undertaken pre- and post-operatively to determine the effects of chronic hyperglucagonaemia on glucose tolerance and glucose kinetics both in the fasting state and during physiological insulin infusions, employing the [3H]-3-glucose technique. In addition the plasma cyclic AMP response to an acute infusion of glucagon was studied pre- and post-operatively. The basal immunoreactive glucagon levels pre- and post-operatively were 10492 +/- 1296 and 149 +/- 15 pg/ml respectively. Pre- and post-operative oral glucose tolerance tests did not differ but were abnormal. Pre-operatively basal hepatic glucose production was normal and it was suppressed rapidly by the low dose insulin infusion, despite continuing hyperglucagonaemia. The metabolic clearance rate of glucose was slightly reduced. There was no plasma cyclic AMP response to a glucagon infusion, suggesting down-regulation of the glucagon receptor by the chronic hyperglucagonaemia. Post-operatively the hepatic glucose production and clearance rate of glucose fell, whereas the plasma cyclic AMP responses to the glucagon infusion reverted to a normal pattern. It is concluded that chronic hyperglucagonaemia is not a major factor in the development of the glucose intolerance, but it may lead to down-regulation of the biological action of glucagon.

Epinephrine and the regulation of glucose metabolism: effect of diabetes and hormonal interactions

Elevations of plasma epinephrine comparable to those observed in physiologic stress, cause a sustained 20--35 mg/dl elevation of plasma glucose in normal humans. This hyperglycemic action is due to a transient increase in hepatic glucose output as well as a reduction in the rate of glucose disposal which accounts for the persistence of hyperglycemia. The latter results from epinephrine-induced suppression of endogenous insulin secretion and, more importantly from a direct inhibitory effect on insulin-stimulated glucose utilization. In diabetes, the hyperglycemic effect of epinephrine is markedly accentuated. The enhanced rise in plasma glucose is due to an alternation in response of the liver to epinephrine. Despite infusion of insulin, epinephrine produces a sustained rather than transient elevation in hepatic glucose output in diabetic subjects. In contrast, the inhibitory effect of epinephrine on glucose utilization is unchanged by the diabetic state. In normal subjects, the hyperglycemic action of epinephrine is enhanced by simultaneous elevations of glucagon and cortisol. The former increases the magnitude, but not the duration, of the rise in hepatic glucose output induced by epinephrine. The latter, converts epinephrine's hepatic action from a transient to a sustained response. Our data thus suggest that marked hyperglycemia in normal subjects requires the concomitant elevation of multiple anti-insulin hormones, whereas such changes may occur in diabetes if any member of this group of hormones is increased. These findings may account for long-standing clinical observation that stress adversely affects blood glucose regulation to a much greater extent in diabetics as compared to normal subjects.

Adrenergic mechanisms for the effects of epinephrine on glucose production and clearance in man

THE PRESENT STUDIES WERE UNDERTAKEN TO ASSESS THE ADRENERGIC MECHANISMS BY WHICH EPINEPHRINE STIMULATES GLUCOSE PRODUCTION AND SUPPRESSES GLUCOSE CLEARANCE IN MAN: epinephrine (50 ng/kg per min) was infused for 180 min alone and during either alpha (phentolamine) or beta (propranolol)-adrenergic blockade in normal subjects under conditions in which plasma insulin, glucagon, and glucose were maintained at comparable levels by infusion of somatostatin (100 mug/h), insulin (0.2 mU/kg per min), and variable amounts of glucose. In additional experiments, to control for the effects of the hyperglycemia caused by epinephrine, variable amounts of glucose without epinephrine were infused along with somatostatin and insulin to produce hyperglycemia comparable with that observed during infusion of epinephrine. This glucose infusion suppressed glucose production from basal rates of 1.8+/-0.1 to 0.0+/-0.1 mg/kg per min (P < 0.01), but did not alter glucose clearance. During infusion of epinephrine, glucose production increased transiently from a basal rate of 1.8+/-0.1 to a maximum of 3.0+/-0.2 mg/kg per min (P < 0.01) at min 30, and returned to near basal rates at min 180 (1.9+/-0.1 mg/kg per min). Glucose clearance decreased from a basal rate of 2.0+/-0.1 to 1.5+/-0.2 ml/kg per min at the end of the epinephrine infusion (P < 0.01). Infusion of phentolamine did not alter these effects of epinephrine on glucose production and clearance. In contrast, infusion of propranolol completely prevented the suppression of glucose clearance by epinephrine, and inhibited the stimulation of glucose production by epinephrine by 80+/-6% (P < 0.001). These results indicate that, under conditions in which plasma glucose, insulin, and glucagon are maintained constant, epinephrine stimulates glucose production and inhibits glucose clearance in man predominantly by beta adrenergic mechanisms.

Role of cyclic AMP in glucagon-induced stimulation of hepatic glucose output in man

The interrelationship between glucagon action on splanchnic glucose output and cyclic AMP production was studied in healthy volunteers after hepatic venous catheterization. Glucagon was infused according to four different protocols to achieve arterial levels ranging from 300 to 9000 ng/l. Infusion of glucagon which resulted in arterial levels of the hormone of 4000-9000 ng/l was associated with a marked increase in net splanchnic cyclic AMP production and in the arterial levels of the cyclic nucleotide. The rise in cyclic AMP efflux from the splanchnic area was transient but an augmented splanchnic production was still evident after 30 min of glucagon infusion. Splanchnic glucose output rose 3-5 fold. Infusion of glucagon at lower rates, resulting in arterial levels of 300-900 ng/l, did not measureably stimulate the efflux of cyclic AMP from the splanchnic area. In spite of this, splanchnic glucose output rose 2-3 fold and the blood glucose level increased 20-50% during glucagon infusion at these lower rates. It is concluded that (1) factors other than cyclic AMP are rate limiting in the stimulation of hepatic glucose production, and (2) although cyclic AMP is an established 'second messenger' of glucagon action, other factors may also be of importance in mediating the physiological response of this hormone.

Differential effects of epinephrine on glucose production and disposal in man

Normal subjects were infused 1) with epinephrine (50 ng/(kg.min)) for 180 min followed by epinephrine plus glucagon (3 ng/(kg.min)) for 60 min after which the epinephrine infusion rate was increased (125 ng/(kg.min)) or 2) with epinephrine plus somatostatin (500 microgram/h) for 180 min. Epinephrine increased glucose production and plasma glucagon transiently but caused persistent suppression of glucose clearance and sustained hyperglycemia (despite increased plasma insulin and gluconeogenic substrates); glucose production increased again on addition of glucagon and on increasing the epinephrine infusion rate. During epinephrine plus somatostatin, glucose production still increased transiently, but further suppression of glucose clearance caused more marked hyperglycemia. In conclusion, 1) in man hyperepinephrinemia within the physiological range caused sustained suppression of glucose clearance but only a transient increase in glucose production; 2) this transient hepatic response a) was not due to glycogen or substrate depletion, b) occurred without changes in plasma glucagon or insulin, c) was specific for epinephrine but permitted subsequent responses to changes in plasma epinephrine; 3) epinephrine can serve as a physiological regulator of glucose homeostasis in man both by increasing glucose production and by decreasing glucose clearance.

Effect of intermittent endogenous hyperglucagonemia on glucose homeostasis in normal and diabetic man

Infusion of glucagon causes only a transient increase in glucose production in normal and diabetic man. To assess the effect of intermittent endogenous hyperglucagonemia that might more closely reflect physiologic conditions, arginine (10 g over 30 min) was infused four times to 8 normal subjects and 13 insulin-dependent diabetic subjects (4 of whom were infused concomitantly with somatostatin to examine effects of arginine during prevention of hyperglucagonemia). Each arginine infusion was separated by 60 min. Diabetic subjects were infused throughout the experiments with insulin at rates (0.07-0.48 mU/kg per min) that had normalized base-line plasma glucose and rates of glucose appearance (Ra) and disappearance (Rd). Basal plasma glucagon and arginine-induced hyperglucagonemia were similar in both groups; basal serum insulin in the diabetics (16+/-1 muU/ml, P < 0.05) exceeded those of the normal subjects (10+/-1 muU/ml, P < 0.05) but did not increase with arginine. Serum insulin in normal subjects increased 15-20 muU/ml with each arginine infusion. In both groups each arginine infusion increased plasma glucose and Ra. Increments of Ra in the diabetics exceeded those of normal subjects, (P < 0.02); Rd was similar in both groups. In normal subjects, plasma glucose returned to basal levels after each arginine infusion, whereas in the diabetics hyperglycemia persisted reaching 151+/-15 mg/dl after the last arginine infusion. When glucagon responses were prevented by somatostatin, arginine infusions did not alter plasma glucose or Ra.

CONCLUSIONS

Infusion of arginine acutely increases plasma glucose and glucose production in man solely by stimulating glucagon secretion; physiologic increments in plasma glucagon (100-150 pg/ml) can result in sustained hyperglycemia when pancreatic beta cell function is limited.

Caval occlusion technique for hepatic venous sampling: a new approach to estimating splanchnic substrate balance in conscious dogs

We have proposed a new technique for sampling hepatic venous blood in conscious dogs. Sub-hepatic vena caval blood flow was temporarily occluded by a previously implanted inflatable snare so that all blood entering the inferior vena cava was hepatic venous effluent. Hepatic venous blood samples were collected from the inferior vena cava 8 seconds after beginning caval occlusion, with the total interval of flow occlusion lasting 12 to 15 seconds. No behavioral or metabolic alterations were observed when or metabolic alterations were observed when hepatic venous effluent was repetitively sampled using the caval occlusion technique. Net splanchnic glucose balance (NSGB) was measured in conscious dogs receiving saline, glucose or glucagon infusions. NSGB measurements made with the caval occlusion technique were in accord with previous results obtained via tracer methodology or arterio-venous difference techniques utilizing hepatic vein catheterization. The caval occlusion technique thus provides a method for collecting hepatic venous blood samples from conscious animals without the difficulties associated with hepatic vein catheterization.

Synergistic interactions of physiologic increments of glucagon, epinephrine, and cortisol in the dog: a model for stress-induced hyperglycemia

To evaluate the role of anti-insulin hormone actions and interactions in the pathogenesis of stress-induced hyperglycemia, the counterregulatory hormones, glucagon, epinephrine, and cortisol were infused alone as well as in double and triple combinations into normal conscious dogs in doses that were designed to simulate changes observed in severe stress. Infusion of glucagon, epinephrine, or cortisol alone produced only mild or insignificant elevations in plasma glucose concentration. In contrast, the rise in plasma glucose produced by combined infusion of any two counterregulatory hormones was 50-215% greater (P < 0.005-0.001) than the sum of the respective individual infusions. Furthermore, when all three hormones were infused simultaneously, the increment in plasma glucose concentration (144+/-2 mg/dl) was two- to fourfold greater than the sum of the responses to the individual hormone infusions or the sum of any combination of double plus single hormone infusion (P < 0.001). Infusion of glucagon or epinephrine alone resulted in a transient rise in glucose production (as measured by [3-(3)H]glucose). While glucagon infusion was accompanied by a rise in glucose clearance, with epinephrine there was a sustained, 20% fall in glucose clearance. When epinephrine was infused together with glucagon, the rise in glucose production was additive, albeit transient. However, the inhibitory effect of epinephrine on glucose clearance predominated, thereby accounting for the exaggerated glycemic response to combined infusion of glucagon and epinephrine. Although infusion of cortisol alone had no effect on glucose production, the addition of cortisol markedly accentuated hyperglycemia produced by glucagon and(or) epinephrine primarily by sustaining the increases in glucose production produced by these hormones. The combined hormonal infusions had no effect on beta-hydroxybutyrate concentration. It is concluded that (a) physiologic increments in glucagon, epinephrine, and cortisol interact synergistically in the normal dog so as to rapidly produce marked fasting hyperglycemia; (b) in this interaction, epinephrine enhances glucagon-stimulated glucose output and interferes with glucose uptake while cortisol sustains elevations in glucose production produced by epinephrine and glucagon; and (c) these data indicate that changes in glucose metabolism in circumstances in which several counterregulatory hormones are elevated (e.g., "stress hyperglycemia") are a consequence of synergistic interactions among these hormones.

Cyclic AMP metabolism and adenylate cyclase concentration in patients with advanced hepatic cirrhosis

Glucagon was tested for its effect on plasma adenosine 3',5'-cyclic monophosphate (cyclic AMP), insulin, and glucose in healthy subjects and in patients with advanced cirrhosis of the liver. In the normal subjects, intravenous infusion of glucagon caused a significant increase in plasma cyclic AMP, glucose, and insulin. In advanced cirrhotics, plasma cyclic AMP, glucose, and insulin did not increase. Adenylate cyclase concentration was measured in liver tissue from end stage cirrhotic patients and from brain-dead organ donors whose cardiovascular function was maintained in a stable state. Basal and total adenylate cyclase concentration were not different in the two groups. Adenylate cyclase from the livers of advanced cirrhotics was, however, significantly less responsive to glucagon stimulation than was that from donor livers. Hepatocytes in advanced cirrhosis have abnormal metabolic behavior characterized by abnormal adenylate cyclase-cyclic AMP response to hormonal stimulation.

Role of glucagon in the pathogenesis of diabetes: the status of the controversy

The current controversy concerning the role of glucagon in the pathogenesis of diabetes is reviewed. The traditional "unihormonal abnormality concept," namely, that all of the metabolic derangements of diabetes are the direct consequence of deficient insulin secretion or activity, and the newer so-called bihormonal abnormality hypothesis, proposing that the fullblown diabetic syndrome requires, in addition to the insulin abnormality, a relative glucagon excess, are scrutinized. The relationship of insulin deficiency to the A-cell malfunction of diabetes, the conflicting evidence concerning the essential role of glucagon in mediating the marked overproduction of glucose and ketones in severe insulin deficiency and the contribution of glucagon to the endogenous hyperglycemia of diabetics without insulin deficiency are examined. Finally, the possibility that therapeutic suppression of diabetic hyperglucagonemia may make possible better control of hyperglycemia than is presently attainable by conventional therapeutic methods is considered. It is concluded that (1) although insulin lowers glucagon levels, restoration to normal of the A-cell dysfunction of diabetes requires that plasma insulin levels vary appropriately with glycemic change; (2) that glucagon mediates the severe endogenous hyperglycemia and hyperketonemia observed in the absence of insulin; (3) that in diabetics in whom insulin is present but relatively fixed an increase in glucagon causes hyperglycemia and glycosuria; and (4) that glucagon suppression could be a potentially useful adjunct to conventional antihyperglycemic treatment of diabetics.

Effect of glucagon on glucose production during insulin deficiency in the dog

The aim of the present experiments was to determine the effects of basal glucagon on glucose production after induction of prolonged insulin lack in normal conscious dogs fasted overnight. A selective deficiency of insulin or a combined deficiency of both pancreatic hormones was created by infusing somatostatin alone or in combination with an intraportal replacement infusion of glucagon. Glucose production (GP) was measured by a primed constant infusion of [3H-3]glucose, and gluconeogenesis (GNG) was assessed by determining the conversion rate of circulating [14C]alanine and [14C]lactate into [14C]glucose. When insulin deficiency was induced in the presence of basal glucagon the latter hormone caused GP to double and then to decline so that after 4 h it had returned to the conrol rate. The conversion of alanine and lactate into glucose, on the other hand, increased throughout the period of insulin lack. Withdrawal of glucagon after GP had normalized resulted in a 40% fall in GP, a 37% decrease in GNG, and a marked decrease in the plasma glucose concentration. Induction of insulin deficiency in the absence of basal glucagon resulted in an initial (30%) drop in GP followed by a restoration of normal GP after 2--3 h and moderately enhanced glucose formation from alanine and lactate. It can be concluded that (a) the effect of relative hyperglucagonemia on GP is short-lived; (b) the waning of the effect of glucagon is attributable solely to a diminution of glycogenolysis because GNG remains stimulated; (c) basal glucagon markedly enhances the GNG stimulation apparent after induction of insulin deficiency; and (d) basal glucagon worsens the hyperglycemia pursuant on the induction of insulin deficiency both by triggering an initial overproduction of glucose and by maintaining the basal production rate thereafter.

Effect of sequential infusions of glucagon and epinephrine on glucose turnover in the dog

Conscious dogs were infused with 1) glucagon (3 ng/kg.min) alone for 120 min followed by glucagon plus epinephrine (0.1 microgram/kg.min) for 60 min and 2) epinephrine alone (150 min) followed by epinephrine plus glucagon for 90 min. Glucagon alone caused a 10--15 mg/dl rise in plasma glucose and a 45% increase in glucose production that returned to baseline by 75--120 min. After addition of epinephrine, glucose production rose again by 80%. Infusion of epinephrine alone resulted in unchanged plasma glucagon levels, a 60--70 mg/dl rise in plasma glucose, and an 80--100% rise in glucose production that returned to baseline by 60--120 min. When glucagon was added, glucose output promptly rose again by 85%. When glucagon was infused alone, there was a rise in glucose uptake, whereas, with epinephrine, glucose uptake failed to rise and glucose clearance fell by 35--50%. We conclude that 1) hepatic refractoriness to persistent elevations of glucagon or epinephrine is specific for the hormone infused; 2) epinephrine stimulates glucose production in the conscious dog in the absence of a rise in plasma glucagon; 3) the hyperglycemic response to glucagon or epinephrine is determined in part by accompanying changes in glucose utilization.

Hyperglucagonemia and its suppression. Importance in the metabolic control of diabetes

The role of glucagon in diabetes was studied in four patients with juvenile-type diabetes during continuous insulin infusion and a diet containing 150 g per day of carbohydrate. During insulin alone, plasma glucagon, measured at two-hour intervals, averaged 182 +/- 34 pg per milliliter, glucose 269 +/- 11 mg per deciliter, glucose excretion 52 +/- 8 g per 24 hours, ketone excretion 1.3 +/- 0.3 mmol per 24 hours, and urea nitrogen 12 +/- 2 g per 24 hours (mean +/- S.E.M.). Somatostatin (2 mg per day) lowered glucagon to 60 +/- 13 pg per milliliter, glucose to 111 +/- 17 mg per deciliter, glucose excretion to 1 +/- 0.7 g per 24 hours, ketone excretion to 0.5 +/- 0.2 mmol per 24 hours and urea nitrogen excretion to 8 +/- 2 g per 24 hours. Replacement of glucagon raised glucagon to 272 +/- 30 pg per milliliter, glucose to 202 +/- 20 mg per deciliter, glucose excretion to 14 +/- 7 g per 24 hours, ketone excretion to 0.8 mmol per 24 hours and urea nitrogen excretion to 11 +/- 2 g per 24 hours. In a subsequent study, similar improvement occurred on a diet of 30 g of carbohydrate daily, when absorption of dietary glucose was negligible. Hyperglucagonemia has an important role in diabetes; its correction reduces diabetic abnormalities to or toward normal.

Glucagon and diabetes

We have considered the evidence, first, that the presence of glucagon is essential in the pathogenesis of the full syndrome that results from complete insulin deficiency; second, that in the diabetic in whom insulin levels are relatively fixed, a rise in glucagon concentration contributes to endogenous hyperglycemia; and, third, that conventional methods of treatment of diabetes do not fully correct either the abnormal glucagon levels or the hyperglycemia, but when insulin therapy is supplemented with somatostatin, an agent which suppresses both glucagon and growth hormone, both hyperglycemia and hyperglucagonemia are corrected. These facts may one day provide a rationale for therapeutic efforts to suppress excess glucagon secretion in the management of diabetes in man.

Pathophysiology of diabetes mellitus

Techniques have been developed for examining the binding of insulin to its target cells and for evaluating the in vivo action of insulin, rekindling interest in the possible role of insulin resistance in adult-onset diabetes. A host of new data have accumulated regarding the contribution of glucagon to the syndrome.

Extrapancreatic glucagon in control of glucose turnover in depancreatized dogs

Depancreatized dogs have plasma immunoreactive glucagon (IRG), which is of gastric origin and is immunologically indistinguishable from pancreatic glucagon. The effects of extrapancreatic IRG on the tracer-determined rate of glucose production were examined to establish whether this hormone contributes to the hyperglycemia observed in six conscious, depancreatized dogs after insulin withdrawal. The dogs were initially maintained normoglycemic with an intraportal insulin infusion. Insulin withdrawal resulted in a 53 and 70% decrease of serum immunoreactive insulin (IRI) at 60 and 210 min, respectively. At 60 min, plasma glucose rose and Ra increased by 50%. A somatostatin-induced decrease in IRG prevented a further increase in Ra and glucose; after somatostatin withdrawal, IRG, Ra, and plasma glucose increased. Arginine given 1 or 3 h after insulin withdrawal increased IRG by 100 pg/ml, and mean Ra rose by 8.9 mg/kg-min. Thus, in depancreatized dogs with low but detectable serum IRI, IRG suppression is associated with inhibition of Ra and further rise in plasma glucose is prevented. Stimulation of IRG release increases Ra and results in marked hyperglycemia. It is concluded that extrapancreatic glucagon has a diabetogenic effect during acute insulin defiency.

Effects of short-time somatostatin infusion on the gastric and intestinal propulsion in humans

The effect of short-time somatostatin infusion on gastric and intestinal propulsion of an oral glucose load was examined in healthy subjects by means of a multiple indicator dilution technique. The early gastric emptying rate was enhanced by somatostatin, indicating delayed gastric inhibition. After withdrawal of the somatostatin infusion, the late gastric emptying rate was decreased and the intestinal propagation rate markedly slowed. The effect of long-time somatostatin infusion has to be examined to analyse the nature of the events described.

Glucose homeostasis during prolonged suppression of glucagon and insulin secretion by somatostatin

Somatostatin was infused for 5-8 hr into five normal men and eleven normal, conscious dogs. This infusion resulted in a persistent decline in plasma glucagon (40-60%) and insulin (30-45%). Plasma gluccose fell 15-25% during the initial 1-2 hr, but subsequently rose to hyperglycemic levels (130-155 mg/100ml) by 3-6 hr, despite persistent hypoglucagonemia. Glucose production initially declined by 40-50%, but later rose to levels 15-20% above basal rates while peripheral glucose utilization fell to levels 20-30% below basal, thereby accounting for hyperglycemia. Infusion of exogenous insulin so as to restore plasma insulin to preinfusion values or cessation of the somatostatin infusion with restoration of endogenous insulin secretion resulted in a prompt reduction of plasma glucose to baseline values. Prevention of the initial somatostatin-induced hypoglycemic response by intravenous infusion of glucose failed to prevent the delayed hyperglycemia. We conclude that somatostatin caused only transient hypoglycemia in normal subjects and that hyperglycemia eventually developes as a consequence of insulin deficiency. These data indicate that basal glucagon secretion is not essential for the development of fasting hyperglycemia and support the conclusion that insulin deficiency rather than glucagon excess is the primary factor responsible for abnormal glucose homeostasis in the diabetic.

Influence of physiologic hyperglucagonemia on urinary glucose, nitrogen, and electrolyte excretion in diabetes

To evaluate the effect of physiologic hyperglucagonemia on nitrogen and glucose metabolism and on urinary electrolyte excretion, pancreatic glucagon was administered as a continuous 3-day infusion to three adult-onset non-insulin-dependent diabetics and two insulin-treated juvenile diabetics while on a constant dietary intake. The glucagon infusion resulted in increases in plasma glucagon which were 4-6 fold greater than control values. Despite prolonged hyperglucagonemia, urinary glucose excretion was unchanged. Similarly, urinary urea nitrogen and total nitrogen excretion were not altered by glucagon administration. Urinary sodium tended to rise, albeit not significantly (p less than .01), on the first infusion day, but later declined to control values despite increasing plasma glucagon concentrations. Urinary chloride, potassium, calcium, phosphorus excretion remained unchanged. We conclude that continuous physiologic increments in plasma glucagon do not enhance glycosuria or increase protein catabolism and ureagenesis in diabetes when insulin is available. The augmented protein catabolism and glucogenesis that accompany diabetic ketoacidosis cannot be explained primarily on the basis of hyperglucagonemia.

Evanescent effects of hypo- and hyperglucagonemia on blood glucose homeostasis

Hypoglucagonemia (induced by somatostatin) and hyperglucagonemia (induced by infusion of physiologic amounts of glucagon) have only evanescent effects on blood glucose regulation. Despite on-going glucagon suppression by somatostatin, fasting hyperglycemia develops within 4-6 hr of insulin suppression, indicating that (1) basal glucagon secretion is not essential for the development of the diabetic state; and (2) insulin-deficiency (rather than altered glucagon secretion) is the dominant long-term factor determining glucose homeostasis in the diabetic. With respect to hyperglucagonemia, only a transient increase in splanchnic glucose output is observed in normal and diabetic subjects in response to physiologic increments in this hormone. The exaggerated hyperglycemic effect of glucagon observed in diabetics1 is thus a consequence of the failure to metabolize the glucose traniently released into the systemic circulation in response to the glucagon rather than a result of persistent stimulation of hepatic glucose production. These observations thus further underscore the essentiality of insulin deficiency in the diabetogenic action of glucagon.