Thomas T. Aoki

Glucagon levels and metabolic effects in fasting man

The role of glucagon in the metabolic adaptation to prolonged fasting in man has been examined. Plasma immunoreactive glucagon was determined during 6-wk fasts and during infusion of exogenous glucagon using an assay which minimized nonpancreatic immunoreactivity. Plasma glucagon concentrations rose twofold to a peak on the 3rd day of fasting and then declined thereafter to a level maintained at or above postabsorptive. Insulin concentration declined to a plateau by the 3rd day. Thus a persisting altered relationship of glucagon and insulin concentrations characterized the fasted state. A synergism of low insulin and relative or absolute elevation of glucagon levels is viewed as a hormonal mechanism controlling the rate of hepatic substrate extraction for gluconeogenesis. Glucagon was infused systemically into 4-6 wk fasted subjects at three dose levels. A marked sensitivity of individual plasma free amino acids to the induced elevations of plasma glucagon within the physiologic range was demonstrated. At higher concentrations, equivalent to those present in the portal vein, stimulation of hepatic gluconeogenesis occurred, and the effects on glucose, insulin, and growth hormone levels and on ketone metabolism were induced.

Muscle and splanchnic glutamine and glutamate metabolism in postabsorptive and starved man

Arterio-venous differences across forearm muscle in man in both prolonged starvation and in the postabsorptive state, show an uptake of glutamate and a relatively greater production of glutamine. Splanchnic arteriovenous differences in the postabsorptive state show a net uptake of glutamine and lesser rate of glutamate production. These data suggest that muscle is a major site of glutamine synthesis in man, and that the splanchnic bed is a site of its removal. The relative roles of liver and other tissues in the splanchnic circuit were not directly assessed, only the net balance. These data in man are in conflict with most previous studies in other species attributing the major proportion of glutamine production to the liver and, pari passu, to the splanchnic bed.

Effect of insulin on muscle glutamate uptake. Whole blood versus plasma glutamate analysis.

For decades, investigators concerned with protein metabolism in man have performed detailed amino acid analyses of human plasma obtained under a wide range of experimental situations. A large body of information has been used to calculated rates of protein synthesis and proteolysis. During the course of an investigation of the effect of intrabrachial artery infusion of insulin (70 muU/min per kg body weight) on glutamate uptake by human forearm muscle, it was discovered that plasma arterio-deep venous glutamate difference analysis failed to document any increase in the uptake of this amino acid, suggesting that insulin had little influence on glutamate uptake by muscle. However, whole blood glutamate analyses, performed on the same blood samples, revealed that (a) the resting muscle uptake of glutamate is smaller than previously reported and (b) insulin is capable of markedly increasing glutamate uptake by muscle from whole blood. Since the hematocrit was obtained on all samples, detailed analyses of the various compartments in which glutamate could be found were performed. It was determined that circulating blood cells have a dynamic role in glutamate transport. These data underscore the need for both whole blood and plasma amino acid analysis in investigations concerned with protein synthesis and/or amino acid flux, for analysis of plasma samples alone could be misleading as illustrated in the present study.

Metabolic Effects of Sodium Bicarbonate in Management of Diabetic Ketoacidosis

Biochemical analyses of blood and cerebrospinal fluid of nine patients with diabetic ketoacidosis and impaired levels of consciousness were performed before and after four hours of intravenous therapy with insulin, saline, and bicarbonate. A comparison with previously reported data from a similar group of patients treated with insulin and saline alone revealed no significant differences in blood or cerebrospinal fluid with the following exceptions. First, the fall in CSF osmolality was significantly less after insulinsaline-bicarbonate therapy than in patients receiving only insulin and saline. Second, CSF pH values declined in both groups with therapy but were significantly lower in the group receiving insulin-saline-bicarbonate. Definite and progressive clinical improvement was noted in all nine patients from admission to discharge. It was concluded that the use of sodium bicarbonate did not discernibly alter the clinical course of the nine patients studied except for the unexplained slower decline in CSF osmolality. The use of NaHCO3 appears to be indicated primarily in situations in which prompt correction of metabolic acidosis is essential, e.g., to improve cardiovascular function.

Amino acid metabolism in lactic acidosis

Abstract Individual plasma amino acid levels have been determined in six patients with severe lactic acidosis. A consistently distorted pattern was observed whether the disorder was due to shock or was of the idiopathic type. A sixfold elevation in mean alanine concentration was observed, and a significant correlation of alanine with pyruvate concentrations was demonstrated. Since alanine is normally released from muscle and stoichiometrically extracted by liver, normal formation of alanine from pyruvate is suggested by the findings. However, uptake and metabolism of alanine by isolated, perfused rat liver was significantly inhibited by perfusate concentrations of lactate and pyruvate equivalent to those observed in the patients. Thus the high levels of alanine in lactic acidosis are viewed as consistent with normal or increased peripheral release combined with impaired hepatic disposal. The levels of fifteen of the nineteen amino acids measured were elevated. Of the remaining four, three were intermediates of the urea cycle.

Peripheral tissue metabolism in cancer-bearing man.

Whole-body tracer studies have documented abnormal glucose and amino acid kinetics in cancer-bearing man. Whether these abnormalities are related to systemic or local tumor effects is questioned. Forearm metabolism was examined in six patients with localized squamous cell carcinoma of the distal esophagus and six healthy normal male volunteers. Substrate arterio-venous differences and blood flow across forearm tissues were determined and substrate flux calculated. The mean forearm blood flow (ml min-1 100 ml forearm-1) was not significantly different between cancer patients (3.67 ± 0.12) and normal subjects (2.80 ± 0.40). The uptake of glucose (μmol min-1 100 ml forearm-1) was significantly higher in cancer patients (1.99 ± 0.45) compared to control subjects without weight loss (0.47 ± 0.18). Lactic acid release (μmol min-1 100 ml forearm-1) was significantly higher in cancer patients (-1.15 ± 0.35) compared to control subjects (-0.26 ± 0.14). There was no significant difference in the flux of individual amino acids between the groups, although the mean total nitrogen released from forearms of cancer-bearing patients was greater than that from normal controls. The arterial serum insulin level was significantly lower and the arterial plasma glucagon level significantly higher in cancer patients compared to control subjects. These data cannot be explained by weight loss alone and suggest a peripheral defect in metabolism in this group of cancer-bearing patients.

Blood Cell and Plasma Amino Acid Levels Across Forearm Muscle During a Protein Meal

To elucidate the role of blood cells in amino acid metabolism, substrate balance across the forearm was studied in a nitrogen-depleted subject fed 200 gm. of meat. After ingestion of the meal, there was the expected outpouring of amino acids from the splanchnic bed into the general circulation. Both cell and plasma levels of most amino acids in arterial blood increased rapidly. Whole blood arterio-deep venous amino acid differences frequently differed from that of plasma. In conclusion, it appears that both blood cells and plasma transport amino acids from the splanchnic bed to the periphery and that both participate actively in the deposition of amino acids in the forearm of the subject studied.

Glucose and Amino Acid Metabolism in Perfused Skeletal Muscle: Effect of Dichloroacetate

Dichloroacetate lowers blood glucose and diminishes blood levels of lactate, pyruvate, and alanine in both starvation and diabetes. To determine the role of skeletal muscle in these changes, studies were carried out in intact rats, with the isolated perfused rat hindquarter and soleus muscle preparation. In hindquarters from fed, starved, and diabetic rats, dichloroacetate alone or in the presence of insulin did not augment glucose uptake. On the other hand, it dramatically curtailed the release of the gluconeogenic precursors lactate, pyruvate, and alanine. Dichloroacetate increased markedly the generation of 14CO2 from lactate-1-14C in starved and diabetic rats, suggesting activation of pyruvate dehydrogenase. The increment in lactate oxidation was stoichiometri-cally equivalent to the decrease in lactate plus alanine release. Glycolysis, as determined from the sum of lactate and alanine release plus lactate oxidation in the hindquarter and from the formation of 3H2O from 3-3H-glucose by the incubated soleus muscle, was not altered by dichloroacetate. Dichloroacetate curtailed the release of most amino acids in the perfused hindquarter of fed rats. In starved and diabetic rats, it caused an increase in the release of valine, leucine, and isoleucine, suggesting inhibition of their metabolism. As judged from lactate-pyruvate and 3-hydroxybutyrate-acetoacetate ratios and changes in tissue α-glycerol-phosphate, perfusion with dichloroacetate caused the cytosol of the muscle cell to become more reduced and the mitochondria more oxidized. Similar changes occurred when it was administered to intact animals. These findings suggest that the hypoglycemic effect of dichloroacetate is, at least in part, due to a decrease in the release of gluconeogenic precursors from skeletal muscle secondary to activation of pyruvate dehydrogenase.

Studies of Glucagon Secretion in Pancreatectomized Patients

Intravenous arginine infusions were performed in two totally pancreatectomized patients and two age/sex-matched normal subjects. Plasma glucagon concentrations did not increase in the pancreatectomized patients, whereas a four- to sixfold rise of the glucagon levels following arginine administration was seen in the control subjects. Measurements of plasma glucagon-like im-munoreactivity revealed no difference between normal and pancreatectomized subjects. The data suggest the absence of a significant number of normally functioning alpha cells in extrapancreatic sites.

Dimethyltriazenoimidazole Carboxamide Therapy of Malignant Glucagonoma

Excerpt Pancreatic alpha cell tumors that secrete glucagon have stimulated considerable interest recently. They have been associated with a striking and distinctive clinical syndrome characterized ...