Fasting glucose production in the smaller of twins with epinephrine-deficient hypoglycemia

The possibility that insufficient glucose production or availability of gluconeogenic substrates could account for fasting hypoglycemia was investigated in three children with epinephrine deficiency. Each had been born the smaller of discordant identical twins, and the unaffected twins served as controls. Fasting plasma glucose production was measured by constant infusion of U-[13]C-glucose under steady-state conditions and was compared with availability of potential glucose sources estimated from respiratory calorimetry and excretory nitrogen. The average rate of glucose production was 2.6 mg/kg/min in the affected twins after they became symptomatic and 2.9 mg/kg/min in the control twins after comparable fasting. Plasma alanine was lower in the affected twins during this interval (average: 0.11 mM versus 0.16 mM), but not earlier prior to decreased plasma glucose; alanine correlated with plasma glucose in a similar way in both groups (r = 0.77). Plasma urea production was 0.30 versus 0.15 mg urea N/kg/min. The calculated availability of potential gluconeogenic amino acids was 1.2 versus 0.6 mg/kg/min. Availability of glycerol, estimated from respiratory calorimetry was 0.4 mg/kg/min in both groups. In two of the twin pairs, net oxidation of carbohydrate (glycogen) was, by design, relatively small under these conditions (0.1 and 0.4 mg/kg/min in the affected and control twins, respectively). Gluconeogenesis therefore accounted for the majority of glucose production. The unaccounted remaining major gluconeogenic source is assumed to be recycled substrates from unoxidized pyruvate. Infusion of excess alanine in these two pairs increased plasma glucose and glucose production similarly in both the affected and control twins. This change was associated with an abnormally large increase in plasma alanine. In the third twin pair, net oxidation of carbohydrate was greater in the affected twin (1.8 versus 1.3 mg/kg/min) and possible glucose sources exceeded total glucose production during hypoglycemia. Earlier during fasting, net oxidation of carbohydrate in this twin was 5.8 mg/kg/min versus 3.1 mg/kg/min in the control. Plasma glucose production measured simultaneously was 4.3 versus 3.8 mg/kg/min, being less than the rate of carbohydrtae oxidation in the affected twin. It is concluded that the abnormal fasting metabolism observed in these children with decreased epinephrine was not primarily a consequence of deficient glucose production or lack of potential gluconeogenic substrates. Initial persistent oxidation of glycogen and subsequent increased utilization of protein during hypoglycemia indicate failure to conserve these limited net sources of pyruvate(AU)

The effect of acidosis on the renal metabolism of glutamine in the rat

Glutamine is the major source of urinary ammonia and this study examines the metabolism of that amino acid in rats under varying acid-base conditions. Other workers have shown that in acidosis there is enhanced renal oxidation of glutamine, which requires increased amounts of acetyl CoA. The present study has shown that during acidosis there was no change in the activity of oxaloacetate decarboxylase and malic enzyme, two enzymes capable of increasing the formation of acetyl CoA. This study also showed that 3-mercaptopicolinic acid inhibited PEPCK - the rate limiting enzyme of gluconeogenesis - and thereby inhibited ammoniagenesis from glutamine mainly by inhibiting deamination. Metabolic acidosis was induced with NH4C1 or HC1. In rats given NH4C1 there was an immediate increase in blood ammonia levels and urinary excretion of ammonia, but this did not occur with rats fed HC1 which showed no change in urinary ammonia but a decrease in urea excretion. Rats fed either NH4C1 or HC1 had similar increases in the plasma concentrations of glutamine, renal PEPCK activity, ammonia and glucose production by renal cortical slices. The time course of changes in metabolic intermediates was measured in rats given NH4C1 or HC1. NH4C1 caused a striking decrease in renal levels of malate, 2-oxoglutarate and phosphoenol pyruvate. Similar changes were observed with HC1, but in addition the levels of glucose and glucose-6-phosphate were elevated. The results of the studies with 3-mercaptopicolinic acid and the metabolite profile in response to acidosis are both constant with the theory that displacement of the glutamic dehydrogenase equilibrium is an important mechanism in the control of glutamine utilisation and the ammoniagenic response to acidosis (AU)

Jamaican vomiting sickness: biochemical investigation of two cases

We identified methylenecyclopropylacetic acid, a known metabolite of hypoglycin A, in the urine of two patients with Jamaican vomiting sickness. Excretion of unusual dicarboxylic acids such as 2-ethylmalonic, 2-methylsuccinic, glutaric, adipic and dicarboxylic acids with eight and 10 carbon chains were also detected in both patients. The amounts of these dicarboxylic acids were 70 to 1000 times higher than normal. These metabolities have also been identified in urine of hypoglycin-treated rats. This evidence links hypoglycin A to Jamaican vomiting sickness as its causative agent. Urinary excretion of short-chain fatty acids was also increased up to 300 times higher than normal. These results indicate that, despite their clinical and histological similarities, the cause and biochemical mechanisms of Jamaican vomiting sickness differ distinctly from those of Reye's syndrome in which these abnormal urinary metabolities are not appreciably increased.(AU)

Counteraction of glucocorticoid - induced hyperglycaemia by hypoglycin

Hypoglycin, B-(methylenecyclopropyl) alanine), administered to starved rats pretreated with corticosterone, caused within 6 hr. a marked decline in blood sugar levels. The findings are evidence that the hypoglycaemic agent imposed a restriction on the rate of gluconeogenesis, against which the multiple actions of the hormone were effective. This conclusion emphasizes the crucial nature of the inhibition which hypoglycin produces in the metabolic sequence of gluconeogenesis (AU)

Effect of starvation on renal metabolism in the rat

The effects of starvation an the acid base status of the rat and on the gluconeogenic and ammoniagenic capacity of rat renal-cortical slices were examined. Starvation for 48 or 72 hrs did not affect acid-base status, and urinary ammonia production did not change. Kidney cortical slices from starved as compared to fed rats showed increased gluconeogenic capicity when incubated with the substrated pyruvate, succinate, fumarate, malate, 2-oxoglutarate, glutamine and glutamate. Renal cortical tissues from starved rats also had increased activity of the gluconeogenic enzyme phosphoenolpyruvate carboxykinase. Renal cortical slices from starved rats did not differ from those of fed rats in the ability to produce ammonia from glutamine or glutamate, nor was there any difference in the activity of glutaminase between these groups. These results show that renal gluconeogenic capacity is increased in starved rats in the absence of systemic acidosis, and starvation does not lead to an increase in urinary ammonia excretion or renal ammoniagenic capacity. (AU)

The effect of malnutrition on the pattern of growth in the rat kidney and the renal response to acidosis

The kidneys of normal rats were analysed for water, fat, protein, RNA and DNA, at 10, 21 and 36 d after birth. The effects on growth caused by two types of malnutrition were investigated. An increase in the RNA:DNA ratio was demonstrated between 10 and 36 d, contrary to previous evidence that this ratio is fixed at birth. Energy deficiency during the first 21 d of life resulted mainly in fewer kidney cells, whereas protein-energy deficiency between 21 and 36 d reulted mainly in a smaller cellular content of RNA and protein. In response to metabolic acidosi, both groups of malnourished rats increased urinary excretion of ammonia and there was enhanced gluconeogenesis in vitro; the basal rate of gluconeogenesis was lower in the protein-energy-deficient rats than in the controls. Protein-energy-deficient rats did not exhibit the renal hypertrophy shown by the control rats in response to acidosis (AU)

Regulation of renal cortex ammoniagenesis. I. Stimulation of renal cortex ammoniagenesis in vitro by plasma isolated from acutely acidotic rats

We studied the acute renal metabolic response in rats made acidotic by a single oral dose of ammonium chloride. Cortical slices from acutely (2-h) acidotic rats utilized more glutamine and produced more ammonia and glucose from glutamine than slices from normal animals. When cortical slices from normal rats were pretreated in vitro with plasma isolated from acutely acidotic rats, they achieved similar increases in glutamine utilization, ammonia formation, and gluconeogensis from glutamine. We did not observe such stimulation in normal cortical slices pretreated in a low pH-low bicarbonate medium. Our data show that a non-dialysable factor is present plasma from acutely acidotic rats that may be responsible for the early increase in the urinary ammonia observed in such animals (AU)

Control of renal cortex ammoniagenesis and its relationship to renal cortex gluconeogenesis

The metabolism of glutamate by kidney cortical slices from normal and acutely acidotic rats and the effect of acidosis in vitro on the metabolism of these two substrates has been investigated. The effects of calcium on all these processes was also studied. Kidney cortical slices from acutely acidotic rats utilized more glutamine and formed more ammonia, glucose and glutamate than slices from rats. Increased glutamine utilization and ammoniagenesis by cortical slices from acidotic rats was not detected when Ca2+ was omitted from the medium, although glucose formation was still enhanced and glutamate formation decreased. With in vitro acidosis there was no change in glutamine uptake in the presence or absence of calcium but with calcium, ammonia production fell. Although there was no change in glutamate uptake by cortical slices from acidotic rats, there was an increase in ammoniagenesis and gluconeogenesis with or without calcium. With in vitro acidosis the only significant changes were an increase in ammoniagenesis and gluconeogenesis in the absence of calcium. The results show that ammoniagenesis from glutamine is controled by a rate-limiting step distinct from that which controls deamination of glutamate and gluconeogenesis from glutamine and glutamate. Possible control points and the interrelationship between ammoniagenesis and gluconeogenesis are discussed (AU)

A study of stabilization of gluconeogenic activity in rat liver slices by calcium and manganese ions

The effect of some bivalent cations on gluconeogenesis by the rat liver-slice preparation has been investigated. Ca2+ and Mn2+ stimulated glucose production from a range of substrates but not from glycerol. Mg2+ had no effect on the rate of glucose production. Ca2+ were required to maintain phosphoenolpyruvate carboxylase activity in the slice preparation. Ca2+ and Mn2+, but not Mg2+, retarded the release of lysosomal enzymes from the slice into the incubation medium. It is proposed that Ca+ and mn2+ stimulate glucose production by stabilizing the lysosome system in the liver-slice preparation. The value of the liver-slice preparation as a means of measuring hepatic gluconeogenesis is discussed (AU)