Hyperammonemia urea excretion

Mitochondrial carbamoylphosphate synthase (ammonia) (EC 2.7.2.S). Extreme hyperammonemia. Elevated glutamine in plasma and cerebrospinal fluid. Urea excretion low. Coma and death usually in postnatal period... 

A number of amino acid transport disorders may be associated with one or several of the systems described in Table 20.4. These are characterized by the excretion of amino acids in the urine but no increase in amino acid levels in the bloodstream. They are usually of hereditary origin. The most common disorder is cystinuria, characterized by the excretion of cystine. Because cystine is only slightly water soluble, cystinuria is often accompanied by the deposition of cystine-containing stones in the genitourinary tract. Cystinuria is apparently caused by a defect in the cationic amino acid transport system. Another disease that affects this system is lysinuric protein intolerance, which is associated with a failure to transport lysine, ornithine, arginine, and citrulline across membranes. Citrulline and ornithine are urea cycle intermediates (see later), and a disruption of their interorgan traffic results in hyperammonemia. 

Other substances to which people have been exposed have been shown to alter the toxic effects of ammonia. Methionine sulfoximine, administered by intraperitoneal injection, suppressed the tonic convulsions produced by intravenous injection of ammonium chloride in mice (Hindfelt and Plum 1975 Warren and Schenker 1964). Intraperitoneal injection of alpha-methylglutamic acid also exerts a protective effect against hyperammonemia in rats (Lamar 1970). Nicotinohydroxamic acid and neomycin administered orally reduce blood ammonia levels and increase excretion of urea in treated rats (Haiada et al. 1985). Ethanol exerted a protective effect on acute ammonia intoxication in mice (O Connor et al. 

The carbonic anhydrase inhibitors cause metabolic acidosis and urinary alkalosis. Patients with severe impairment of liver function are unahle to synthesize urea efficiently and become dependent on renal excretion of ammonium ion to rid the body of nitrogenous wastes. However, in alkaline urine the ammonium ion is rapidly converted to ammonia gas. which is veiy rapidly reabsorbed. Hyperammonemia results, with severe neurologic consequences. The answer is (A). 

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