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Biomedical subjects

M Watford

Publications and source records attributed to M Watford.

50 records · Page 3Linked to original sources
PubMed1987

The synthesis of glucose and ammonia by kidney tubules isolated from suckling and early-weaned lambs.

Glucose and ammonia production were examined in kidney tubules isolated from suckling and early-weaned lambs, on days 10-30 after birth, with abrupt weaning occurring at day 14. There were no differences in the rates of glucose or ammonia production for a given substrate by tubules isolated from any of the lambs, regardless of age or stage of weaning. The preferred substrates for gluconeogenesis were glycerol = lactate greater than propionate = pyruvate = fructose = proline greater than alanine greater than glutamate greater than glutamine greater than aspartate greater than glycine greater than serine, and for ammoniagenesis were glutamine much greater than alanine greater than aspartate much greater than serine greater than glycine = glutamate = proline.

Aging↗
PubMed1985

Gluconeogenesis in the chicken: regulation of phosphoenolpyruvate carboxykinase gene expression.

In chickens, the liver functions in gluconeogenesis to recycle lactate carbon (Cori cycle) and the kidney is the major organ for net gluconeogenesis from substrates such as pyruvate and amino acids. This is markedly different from mammalian systems where the liver is the primary gluconeogenic organ. The limited ability of chicken hepatocytes to synthesize glucose is explained, at least in part, by the observation that phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) in these cells is located exclusively in the mitochondria. The kidney possesses a cytosolic form of this enzyme that adapts to dietary and acid-base stimuli. The relative abundance of mRNA coding for the cytosolic enzyme has been detected by using a specific cDNA probe. Starvation increases the level of this mRNA in chicken kidney and also results in the appearance of the message in chicken liver. Isolated hepatocytes have been used to determine which hormones regulate expression of the hepatic gene. Incubations with glucagon, epinephrine, norepinephrine, dexamethasone, or dibutyryl cyclic AMP increase the relative abundance of the message in liver cells isolated from fed chickens. Despite considerable levels of this mRNA in the liver of starved chickens, functional cytosolic enzyme activity is not detected. This indicates some form of posttranscriptional regulation. The studies summarized illustrate the usefulness of isolated hepatocytes and recombinant DNA probes in the study of hormonal regulation of hepatic gene expression.

Animals↗
PubMed1984

The regulation of phosphate-activated glutaminase activity and glutamine metabolism in the streptozotocin-diabetic rat.

The activity of phosphate-activated glutaminase was increased in the kidney, liver and small intestine of rats made diabetic for 6 days with injection of streptozotocin (75 mg/kg body wt.). Insulin prevented this increase in all three tissues. Treatment with NaHCO3, to correct the acidosis that accompanies diabetes, prevented the increase in renal glutaminase activity, but not that in liver or small intestine. Chemically induced acidosis (NH4Cl solution as drinking water) or alkalosis (NaHCO3 solution as drinking water) increased and decreased, respectively, glutaminase activity in the kidney, but were without significant effect on the activity in liver and small intestine. The increase in glutaminase activity in the small intestine during diabetes was due to an overall increase in the size of this organ, and was only detectable when activity was expressed in terms of whole organ, not mucosal scrapings or isolated enterocytes. Prolonged diabetes (40 days) resulted in an even greater increase in the size and glutaminase activity of the small intestine. Despite this marked increase in capacity for glutamine catabolism, arteriovenous-difference measurements showed a complete suppression of plasma glutamine utilization by the small intestine during diabetes, confirming the report by Brosnan, Man, Hall, Colbourne & Brosnan [(1983) Am. J. Physiol. 235, E261-E265].

Animals↗
PubMed1980

The regulation of glucose and pyruvate formation from glutamine and citric-acid-cycle intermediates in the kidney cortex of rats, dogs, rabbits and guinea pigs.

The suppression by 3-mercaptopicolinate of gluconeogenesis from glutamine or 2-oxoglutarate in rat or dog kidney tubules did not affect the amount of these substrates undergoing complete oxidation. Furthermore, 3-mercaptopicolinate caused an accumulation of lactate in dog tubules. 3-Mercaptopicolinate abolished both gluconeogenesis and substrate oxidation in tubules from rabbit and guinea-pig kidney. These results imply the presence of an alternative pathway to phosphoenolpyruvate carboxykinase/pyruvate kinase for the production of pyruvate from citric-acid-cycle intermediates in the kidney cortex of rats and dogs but not in that of rabbits or guinea pigs. Oxaloacetate decarboxylase (present in the kidney cortex of all four species) or 'malic' enzyme (present in rat and dog but absent in rabbit and guinea-pig kidney cortex) could function in this role. Our observations indicate that 'malic' enzyme is probably implicated in this phenomenon. The lactate production observed in dog tubules in the presence of 3-mercaptopicolinate can be suppressed when aspartate formation is inhibited by 2-amino-4-methoxy-trans-but-3-enoic acid. This suggests that the provision of cytosolic NADH from citric-acid-cycle intermediates is facilitated by accumulation of aspartate acting as a 'sink' for cytosolic oxaloacetate.

Animals↗
PubMed1980

Changes in renal metabolite profile and ammoniagenesis during acute and chronic metabolic acidosis in dog and rat.

Acute metabolic acidosis was induced by an i.v. administration of hydrochloric acid to dogs and rats to decrease the plasma bicarbonate concentration from 22 to 12 mM in dogs and from 26 to 10 mM in rats. Chronic metabolic acidosis was also induced in dogs by ammonium chloride feeding for 5 days. Rats also were given ammonium chloride for 24 hours. The renal metabolite profile was determined on the freeze-clamped renal tissue before and after 100 min (dogs) or 30 to 240 min (rats) of acsute acidosis. Measurements on chronically acidotic dogs and rats with 24-hour acidosis were obtained also for comparison with acute acidosis. In both species, kidney glutamine, glutamate, and alpha-ketokglutarate concentrations decreased drastically following induction of acute or chronic acidosis, In the dog, or in the rat during the first 2 hours of acidosis, malate concentration was unchanged. Malate concentration fell significantly in the rat kidney only after 2 hours of acidosis without change in phosphoenolpyruvate (PEP) concentration. In chronically acidotic dogs, malate and oxaloacetate rose fivefold with no change in PEP concentration. Phosphoenolpyruvate carboxykinase (PEPCK) activity was not stimulated by chronic metabolic acidosis in the dog in contrast to the rat. Acute acidosis by hydrochloric acid increased net renal glutamine extraction in the rat but not in the dog. These data suggest that an increased metabolic flux occurs between alpha-ketoglutarate and malate in both rat and dog kidney during acute metabolic acidosis. In the rat, however, after 2 hours, PEPCK activation modifies the kidney metabolite profile. Intrarenal glutamine transport seems to be a rate-limiting factor for adaptation to acute acidosis in the dog but not in the rat kidney.

Acidosis↗
PubMed1980

Inhibition of renal gluconeogenesis and phosphoenolpyruvate carboxykinase activity by 3-mercaptopicolinic acid: studies in rat, guinea pig, dog, rabbit, and man.

The inhibition of gluconeogenesis in isolated kidney tubules by 3-mercaptopicolinate, a specific inhibitor of the phosphoenolpyruvate carboxykinase reaction, is species specific. At any given concentration of the inhibitor, the degree of inhibition is in the order rat > guinea pig greater than or equal to man > rabbit greater than or equal to dog. The intracellular distribution of PEPCK activity (as measured in both the forward and backward directions) supports the conclusion that in the intact cell the cytosolic enzyme is preferentially inhibited. Analysis of the inhibition failed to demonstrate any significant differences between the enzymes, regardless of intracellular or animal source. All enzymes exhibited a similar Ki (2--10 microM) for 3-mercaptopicolinate when assayed in the forward direction. The observed preferential cytosolic inhibition could be due to either in situ differences in metallic ions concentration or a restriction in mitochondrial permeability for mercaptopicolinate.

Animals↗
PubMed1979

Isolation and metabolic characteristics of rat and chicken enterocytes.

1. The recent recognition of the metabolic, as opposed to absorptive, functions of the small intestine prompted efforts the improve the preparation of metabolically competent columnar absorptive cells ('enterocytes') and to study their metabolic properties. 2. With this preparation, linear rates of O2 consumption are obtained for 40 min at 37 degrees C that are more than 50% higher than rates reported by other authors. 3. Among added substrates, glucose, glutamine and glutamate are the preferred fuels of respiration. The main nitrogenous products of glutamine metabolism are NH3, alanine and glutamate. Glutamine carbon was not detectable in citrulline or proline, in contrast with the findings of Windmueller & Spaeth [(1974) J. Biol. Chem. 249, 5070-5079] in the vascularly perfused small intestine. 4. The rates of O2 uptake in the presence of glutamine or glutamate are sufficient to account for the formation of the carbon skeleton of alanine from the amino acid substrate, i.e. the ratio of O2 used/alanine formed is greater than 1.5. 5. Added ADP and ATP are rapidly degraded to AMP and IMP to a large extent by release of hydrolytic enzymes from the enterocytes into the medium. 6. Chicken enterocytes isolated by the same method are more stable; linear rates of O2 uptake are maintained for 60-70 min.

Adenine Nucleotides↗