Ammonium Uptake by the Extremities and Brain in Hepatic Coma, 12

Ammonium salts have been shown to have significantly different toxicities (LD,0's) when administered intravenously under controlled conditions (1). This differential toxicity appeared to be related to the change in blood pH induced by each salt.The normal blood pH (7.4) is close enough to the pKbh of ammonia,2 approximately 8.90 at 370 C. (2), so that any change in blood pH would significantly affect the ratio of unionized (NH8) to ionized (NH4+) ammonia. Based on two factors, the greater tissue permeability to unionized particles (3-6) and the marked limitation of passage of ionized particles by the blood-brain-barrier (7-9), it was postulated that a greater percentage of a given dose of ammonia might enter the brain as the blood pH rose because of an increase in the amount present as NH3.In order to test this hypothesis, blood pH and simultaneous blood and brain ammonia concentrations were determined following the intravenous administration of LD50 doses of several ammonium salts. This was done on the assumption that since the primary toxic effect of ammonia appeared to be located in the central nervous system the brain levels would be relatively similar despite different LD50 dosages of each salt. MATERIALS AND METHODSLD.4 doses (1) of five ammonium salts dissolved in 1 ml. of isotonic saline were rapidly injected into the tail veins of 18 to 22 Gm. Swiss albino mice. Heart blood was drawn at various intervals after injection. Immediately thereafter the mice were frozen in liquid nitrogen.The blood ammonia concentration in a protein free preparation of 0.5 to 1.0 ml. of heart blood was determined by. a microdiffusion technique (10). The control blood 1 Present address: Peter Bent Brigham Hospital, Boston, Mass.2The term "ammonia" refers to ammonium ion plus free ammonia.ammonia concentration was 0.6 Iug. per ml. Brain ammonia levels were determined by a modification (11) of this technique utilizing the entire frozen mouse brain. The brain was shelled out, ground to a fine powder with cold instruments, and added to 3 ml. of 3 per cent cold trichloracetic acid. The tubes were weighed before and after the brain was added, and were centrifuged at 3°C. The ammonia concentration of a 1 ml. aliquot of the supernatant was then measured by the previously mentioned method (10) and the brain ammonia calculated from these data. Glutamine amide error was a constant 22 per cent of the control ammonia concentration of 4.0 ug. per Gm. of wet brain. The pH of heparinized heart blood obtained from live unanaesthetized animals was immediately determined at room temperature with a Beckman Model GS meter equipped with a 290-80 blood electrode.Electrocardiograms were obtained from pentobarbital anaesthetized mice during the intravenous injection of LD, doses of the five ammonium compounds. Electrodes were implanted subcutaneously as limb leads, and the recording was made on a Sanborn polyviso recorder. RESULTSMice injected with ammonium chloride immediately demonstrated agitated movements followed rapidly by the onset of coma. ...

Section: Discussionmentioning

confidence: 99%

The Passage of Ammonia Across the Blood-Brain-Barrier and its Relation to Blood pH

Warren¹,

Nathan²

1958

“…In humans, direct measturemiients of' the arterial andcl cerebral venous concentration differences for ammonia have failed to show a consistent pattern for brain ammonia metabolism. Although most data indicate that the brain extracts a small fraction of the ammonia present in arterial blood (25,26), other data show no extraction or ammonia production (27). The failure to demonstrate that ammonia enters the brain has been cited as a weakness in the hypothesis that hyperammonemia produces hepatic encephalopathy (2).…”

Section: * Includes Isotope In Tumormentioning

confidence: 99%

The dynamics of ammonia metabolism in man. Effects of liver disease and hyperammonemia.

Lockwood¹,

McDonald²,

Reiman³

et al. 1979

375

201

A B S T R A C T The cyclotron-produced radionuclide, 13N, was used to label ammonia and to study its metabolism in a group of 5 normal subjects and 17 patients with liver disease, including 5 with portacaval shunts and 11 with encephalopathy. Arterial ammonia levels were 52-264 ,AM. The rate of ammonia clearance from the vascular compartment (metabolism) was a linear function of its arterial concentration: Amol/min = 4.71 [NH3Ia + 3.76, r = +0.85, P < 0.005. Quantitative body scans showed that 7.4+±0.3% of the isotope was metabolized by the brain. The brain ammonia utilization rate, calculated from brain and blood activities, was a function of the arterial ammonia concentration: ,umol/ min per whole brain = 0.375 [NH3]a -3.6, r = +0.93, P < 0.005. Assuming that cerebral blood flow and brain weights were normal, 47 + 3% of the ammonia was extracted from arterial blood during a single pass through the normal brains. Ammonia uptake was greatest in gray matter. The ammonia utilization reaction(s) appears to take place in a compartment, perhaps in astrocytes, that includes <20% of all brain ammonia. In the 11 nonencephalopathic subjects the [NH3Ia was 100±8 ,uM and the brain ammonia utilization rate was 32±3 ,umol/min per whole brain; in the 11 encephalopathic subjects these were respectively elevated to 149±18 AM (P < 0.01), and 53 ± 7 ,umol/min per whole brain (P <0.01). In normal subjects, -50% of the arterial ammonia was metabolized by skeletal muscle. In patients with portal-systemic shunting, muscle may become the most important organ for ammonia detoxification.

“…Exercising muscle releases NH3 into the venous return (34,35). Brain and other peripheral tissues may release ammonia under certain conditions (36). The possible role of the widely distributed amine oxidases acting on circulating amines has been mentioned (37).…”

Section: Filtrate Stabilitymentioning

confidence: 99%

The Existence of Ammonia in Blood in Vivo With Observations on the Significance of the Nh4+–nh3 System *

Bromberg

Robin²,

Forkner³

1960

The development of refined methods for determination of blood ammonia in the past 50 years has resulted in a gradual lowering of the reported concentrations in the peripheral venous blood of normal man (1). After extensive work with a microdiffusion technique, Conway and Cooke concluded that the normal in vivo peripheral venous level of the blood ammonia nitrogen in man was operationally zero, but that rapid liberation of ammonia from certain precursors occurred after shedding to produce in vitro values of about 35 Amoles ammonia-nitrogen (NH3-N) per L blood (2). Identical conclusions were reached by Koprowski and Uninski in their work on dog blood (3), using Conway's method. The results of more recent investigations using different techniques (4-7) have indicated that peripheral venous blood does contain significant amounts of ammonia in vivo. This conflict has not been resolved despite frequent use of the Conway method in many investigations of human ammonia metabolism in the past decade.The present experiments were stimulated by the observation that dogs receiving intravenous infusions of ammonium salts excreted measurable amounts of NH8 gas in expired air (8). This ammonia was presumably derived from the dissolved NH. gas which must exist in equilibrium