The intravenous L-alanine tolerance test as a means for investigating gluconeogenesis
1974; Elsevier BV; Volume: 23; Issue: 12 Linguagem: Inglês
10.1016/0026-0495(74)90031-6
ISSN1532-8600
Autores Tópico(s)Metabolism and Genetic Disorders
ResumoGluconeogenesis was tested in eight children with abnormalities of carbohydrate metabolism by means of the intravenous injection of 0.5 g L-alanine per kilogram body weight. The test was performed on two girls with debranching enzyme-deficient glycogenosis, two brothers with phosphorylase-deficient glycogenosis, three boys with ketotic hypoglycemia, and one boy with fructose-1,6-diphosphatase deficiency. The former seven patients showed a marked increase of the initially low fasting blood glucose levels after alanine injection, whereas the last patient merely responded with a further increase of the initially high blood lactate concentration, glucose levels remaining as low as before the test. An intravenous glycerol tolerance test was characterized by the same response. The blood alanine concentrations, determined in three patients of the former group, decreased rapidly after alanine injection, whereas the patient with a fructose-1,6-diphosphatase deficiency showed a delayed alanine elimination. The results pointed to unimpaired gluconeogenesis of the first seven patients and a defective glucose formation in the eighth patient. It is discussed that the intravenous alanine tolerance test permits gluconeogenesis to be regarded as normal or impaired only, if the previous fast of the patient has been sufficiently long. In the case of impaired gluconeogenesis, an additional tolerance test, with a glucogenic substrate that enters the gluconeogenic pathway at a level different from alanine, facilitates the localization of the enzyme defect underlying the impaired gluconeogenesis.
Referência(s)