Mackenzie Walser

ION ASSOCIATION. VI. INTERACTIONS BETWEEN CALCIUM, MAGNESIUM, INORGANIC PHOSPHATE, CITRATE AND PROTEIN IN NORMAL HUMAN PLASMA

The total measured concentration of an ionizable constituent of body fluids often fails to reveal either the varied chemical forms in which it may be present, or the portion which is present as the free ionized substance. This truism applies to most organic acids and bases and to inorganic ions which are multivalent. Univalent ions whose cor

AN EVALUATION OF RADIOSULFATE FOR THE DETERMINATION OF THE VOLUME OF EXTRACELLULAR FLUID IN MAN AND DOGS

Reasonably satisfactory methods have been developed for estimation of plasma volume (1) and total body water (2, 3) in normal subjects. On the other hand, no entirely satisfactory substance for estimating the volume of the extracellular fluid has as yet been found. It is not surprising that the material for this purpose should be more difficult to select, since, in order to have a volume of distribution equal to the extracellular fluid, it must be capable of passing through one membrane, the capillary wall, and yet be effectively excluded by the other, the cell wall. The use of large molecules such as inulin (4, 5) and sucrose (6, 7), which are excluded for the most part from body cells, is restricted by their slow rate of capillary diffusion, particularly in the case of inulin, which generally necessitates a constant infusion and limits the applicability of these methods in edematous states (8). Mannitol, which diffuses more rapidly (9, 10), suffers from the disadvantage of changing extracellular fluid in two ways in the process of measuring it, because the plasma concentration required for accurate analysis exerts an effective osmotic pressure which draws water from cells, thereby expanding extracellular fluid volume, at the same time that a mannitol diuresis is sweeping sodium chloride into the urine. Several ions which diffuse rapidly into the interstitial fluid have been employed for the measurement of extracellular volume, including bromide (11, 12), thiocyanate (7), thiosulfate (13, 14), ferrocyanide (15), and sulfate (7, 16). Bromide (17), thiocyanate (7, 18), and thiosulfate (13) all penetrate cells to a significant extent. Thiosul-

The Effect of Keto-analogues of Essential Amino Acids in Severe Chronic Uremia

Alpha keto-analogues of valine, leucine, isoleucine, methionine, phenylalanine, and (in one instance) tryptophan and histidine, along with the remaining essential amino acids, were administered orally to 10 patients with severe chronic uremia fed a diet low in protein but adequate in calories. Ketoacid dosage varied from 6 to 14 g daily, as sodium or calcium salts. Net nitrogen intake, calculated as intake minus urinary protein nitrogen, averaged 1.8 g/day. The urea space was either estimated or measured with [(14)C]urea and daily changes in the body urea pool were calculated. Urea appearance was measured as the sum of urea excretion and the change in urea pool. If these ketoacids were converted to amino acids and utilized for protein synthesis, a fall in urea nitrogen appearance should occur. In five subjects, ketoacids were given for 15-18 days and then withdrawn. Urea nitrogen appearance increased 1.55 g/day on withdrawing ketoacids, and corrected nitrogen balance decreased by 1.73 g/day. In two other subjects ketoacid administration was followed, on two occasions each, by a period of administration of nine essential amino acids. In three of these four instances, urea appearance rose significantly with amino acids. In four patients studied at high blood urea levels, ketoacid treatment was relatively ineffective; two of these patients responded more favorably when studied again after peritoneal dialysis. One of these improved enough clinically to be managed as an out-patient for short intervals, despite virtual anuria. No accumulation of ketoacids in plasma or urine could be detected, and no toxicity was identified.

Nitrogen sparing induced by leucine compared with that induced by its keto analogue, alpha-ketoisocaproate, in fasting obese man.

We measured the effects of seven consecutive daily infusions of alpha-ketoisocaproate (the alpha-keto analogue of leucine) or leucine itself on urinary urea and total nitrogen excretion during fasting. Two study protocols were undertaken. In protocol I, subjects underwent three separate 14-d fasts: one during which 34 mmol/d of leucine were infused on days 1--7; a second during which 34 mmol/d of alpha-ketoisocaproate were infused on days 1--7; and a third control fast during which no infusions were given. Infusions of alpha-ketoisocaproate significantly reduced daily urine urea nitrogen excretion compared with both the control fasts and the fasts in which leucine was infused (P less than 0.001). This nitrogen-sparing effect of alpha-ketoisocaproate persisted during days 8--14 even though no further infusions were given. Daily urinary urea nitrogen excretion during fasts when leucine was administered did not differ from values observed during control fasts. In protocol II, subjects were starved on two occasions for 14 d. During one fast, infusions of 11 mmol/d of alpha-ketoisocaproate were given on days 1--7; during the control fast, no infusions were given. Daily urine urea nitrogen excretion was lower (P less than 0.001) on days 1--7 and also on days 8--14 of the fast during which alpha-ketoisocaproate was given. The nitrogen-sparing effect of alpha-ketoisocaproate could not be related to changes in circulating levels of amino acids, ketone bodies, or insulin in either protocol. We conclude that alpha-ketoisocaproate infusions decrease the nitrogen wasting of starvation, whereas leucine, studied under identical conditions, does not.

Synthesis of Essential Amino Acids from Their α-Keto Analogues by Perfused Rat Liver and Muscle

Abstract Most essential amino acids can be replaced by their α-keto-analogues in the diet. These ketoacids have therefore been proposed as substitutes for dietary protein. In order to determine their fate in tissues of normal animals, isolated rat liver and hindquarter (muscle) preparations were perfused with keto-analogues of valine, leucine, isoleucine, methionine, or phenylalanine. When perfused at 1.5-2.0 mM, all five compounds were utilized rapidly by the liver of 48-h starved rats, at rates varying from 49 to 155 μmol/h per 200g rat. The corresponding amino acids appeared in the medium in significantly increased concentrations. Perfusion with phenylpyruvate also led to the appearance of tyrosine. Urea release was unaltered. Measurement of metabolite concentrations in freeze-clamped liver revealed two abnormalities, particularly at ketoacid concentrations of 5 mM or above: a large increase in α-ketoglutarate, and a moderate to marked decrease in tissue glutamine. This decrease was quantitatively sufficient to account for nitrogen appearing in newly synthesized amino acids. Isolated hindquarters of fed rats were perfused with the same ketoacids at concentrations of 1.3-8.0 mM. All were utilized at rates varying from 1.4 to 7.0 μmol/h per g muscle perfused. The corresponding amino acids were released at greatly increased rates. Alanine and glutamate levels fell in some perfusions, but the principal nitrogen donor in muscle was not identified; the content of glutamine in tissue, and its rate of release into the perfusate remained constant.

Urea Metabolism in Chronic Renal Failure

Urea degradation was measured during 16 experiments in 13 chronic uremic patients being treated with essential amino acids or their analogues. [(14)C]Urea was injected i.v. and the clearance of labeled urea from its volume of distribution was compared with the simultaneous renal clearance of ordinary urea, which averaged 2.0 liters/day. The difference, extrarenal clearance of urea, averaged 3.1 liters/day as compared with a previously reported mean of 18 liters/day in normal subjects. Thus urea-splitting activity in the gut of uremic subjects expressed in these terms is far less than in normal individuals. Nevertheless, the amount of ammonia N formed from urea in these patients, 3.5 g/day, is not significantly different from normal, owing to their elevated plasma urea. In the same subjects, urea appearance rate was measured as the sum of urea excretion and the daily change in the urea pool. No negative correlation was noted between urea appearance and urea degradation, as might be expected if portal ammonia were being utilized for protein synthesis. However, urea production was positively correlated (r = 0.76) with urea degradation, suggesting that most of the resulting portal ammonia is converted back to urea. The results fail to support the view that degradation of urea in the gut promotes N conservation in uremic subjects maintained on low protein diets.

Gyrate atrophy of the choroid and retina: amino acid metabolism and correction of hyperornithinemia with an arginine-deficient diet.

Four patients with gyrate atrophy of the choroid and retina were studied, all of whom exhibited the hyperornithinemia characteristic of this disorder. Elevated plasma histidine and diminished plasma lysine and branched-chain amino acids were also noted. The renal clearances of these four amino acids were not sufficiently elevated to explain their low plasma levels. In one subject, an arginine-deficient diet led to progressive reduction in plasma ornithine from 13 times normal to the upper limits of normal, along with the disappearance of ornithinuria and lysinuria. Orally administered alpha-aminoisobutyric acid facilitated the fall in plasma ornithine by increasing renal losses of ornithine. It also increased the clearances of most other amino acids. When plasma ornithine approached normal (less than 200 microM), plasma lysine became normal, plasma arginine became subnormal, and renal clearances of basic amino acids decreased. Long-term (1.5 yr) maintenance with a diet containing 10-20 g of protein plus essential amino acids served to keep plasma ornithine at between 55-355 microM; chorioretinal degeneration did not progress and vision apparently improved.

Nitrogen Sparing Induced by a Mixture of Essential Amino Acids Given Chiefly as Their Keto-Analogues during Prolonged Starvation in Obese Subjects

11 normal obese subjects were fasted for 33 days. In five, who served as controls, urine urea nitrogen excretion remained constant for 2 wk thereafter. The other six were given seven daily infusions containing 6-8 mmol each of the alpha-keto-analogues of valine, leucine, isoleucine, phenylalanine, and methionine (as sodium salts) plus 3-4 mmol each of the remaining essential amino acids (lysine, threonine, tryptophan, and histidine). Rapid amination of the infused ketoacids occurred, as indicated by significant increases in plasma concentrations of valine, leucine, isoleucine, alloisoleucine, phenylalanine, and methionine. Glutamine, glycine, serine, glutamate, and taurine fell significantly. Blood glucose, ketone bodies, plasma free fatty acids, and serum immunoreactive insulin concentrations were unaltered. Urine urea nitrogen fell from 1.46 to 0.89 g/day on the last day of infusions; 5 days later it was still lower (0.63 g/day) and in two subjects studied for 9 and 17 days postinfusion it remained below preinfusion control values. Urine ammonia, creatinine, and uric acid were unaltered. Nitrogen balance became less negative during and after infusions. The results indicate that this mixture of essential amino acids and their keto-analogues facilitates nitrogen sparing during prolonged starvation, in part by conversion of the ketoacids to amino acids and in part by altering mechanisms of nitrogen conservation. The latter effect persists after the ketoacids are metabolized.

Reversible stimulation of sodium transport in the toad bladder by stretch

Short-circuit current and transepithelial potential difference were measured in toad hemibladders mounted as sacs on glass cannulae. When sac volume was changed by adding or removing fluid, short circuit current responded by increasing or decreasing during the ensuing half-hour. The time course of the response and its magnitude indicated that it was not artefactual. Furthermore, net sodium flux responded similarly. Sac volume, and thus bladder surface area, could be varied from 0.03 to 0.4 cm(2)/mg wet weight. The mean response to either decreases or increases was 10 muA/cm(2). Everted hemibladders, however, responded less. Neither hydrostatic pressure, nor increased chloride conductance, nor increased access of oxygen or glucose to the mucosa was responsible for the response. Tissue conductance did vary markedly with volume, and may have played a role, but sodium conductance did not vary with volume in a consistent manner. The results indicate the existence of an intrinsic mechanism in this tissue which alters sodium transport in response to stretch.

Plasma α-Ketoglutarate in Urea Cycle Enzymopathies and Its Role as a Harbinger of Hyperammonemic Coma

Summary: Metabolic observations during early stages of hyperammonemia in two infants with ornithine transcarbamylase deficiency suggest that plasma α-ketoglutarate concentration ([α-KG]) becomes subnormal before the development of hyperammonemic coma. In one case, plasma [NH4+] remained normal until 40 days of age when it rose to 57 μM. However, this hyperammonemia was preceded by a fall in plasma [α-KG] to 15 μM at 27 days of age. It was only after severe hyperammonemia was established at 50 days of age that coma supervened. In the second case, plasma [α-KG] became subnormal (14 μM) 8 days before the rise in plasma ammonium concentration [NH4+] (52 μM) and 14 days before the onset of hyperammonemic coma. In eight patients with urea cycle enzymopathies, there was a highly significant (P ≤0.01) negative linear correlation between [NH4+] and [α-KG]. In patients with portal-systemic encephalopathy, there was a similar relationship between [NH4+] and [α-KG], although the absolute [α-KG] levels in these patients were normal (23 ± 4 μM) while the patients were hyperammonemic (88 ± 25 μM).Speculation: The inverse linear correlation between [α-KG] and [NH4] levels in patients with urea cycle enzymopathies suggest that plasma [a-KG] may presage hyperammonemic coma. However, the different [a-KC] levels in patients with cirrhosis and portalsystemic shunting imply different pathophysiologic mechanisms for hyperammonemic coma as compared to hepatic coma.