Pancreatic alpha- and beta-cell function and metabolic changes during oral L-alanine and glucose administration:...

The present study investigated whether or not, in addition to the oral glucose tolerance test, oral alanine loading was a useful diagnostic tool for hormonal and metabolic diseases. Fifty g of L-alanine was administered orally in 14 normal, 12 diabetic, and 8 liver cirrhotic subjects. The influence of oral alanine loading on hormones and metabolites was compared with the results of 100 g oral glucose loading. The results obtained were as follows: 1) In the normal subjects and cirrhotics, lactate and pyruvate concentrations gradually increased with time and reached their peak levels at 60 min, whereas they remained unchanged throughout the course in the diabetic group at glucose loading. 2) Alanine administration accelerated ureogenesis but did not affect blood glucose levels. 3) In both glucose and L-alanine administration, free fatty acid, glycerol and ketone body levels declined nonspecifically in all groups. 4) Serum glucagon levels during L-alanine loading increased in all groups, especially in liver cirrhotics. 5) L-alanine was a potent stimulus for insulin secretion in diabetics, while no insulin release during glucose loading was observed. 6) The molar ratio of insulin levels (during glucose loading)/glucagon levels (during L-alanine loading) was a good indicator of systemic glucose homeostasis from the hormonal aspect. It is suggested that, in addition to the oral glucose tolerance test, the oral administration of L-alanine can be a useful tool for the diagnosis of the status in diabetes mellitus and cirrhosis.