Glucose and free amino acids in the blood of lampreys (Lampetra fluviatilis L.) and frogs (Rana temporaria L.) under prolonged starvation

The content variation dynamics of glucose and free amino acids in blood plasma was followed for lampreys and frogs from autumn till spring, when the exogenous feeding is switched off. In October, the glucose level is rather high (8-10 mM) in blood plasma of both lampreys and frogs. It falls by 50% during winter and falls to a critically low level (1-2 mM) during spring. The lamprey plasma amino acid levels increase by 74% from November to April and thus reach the lower limit known for mammals. The amount of free amino acids in frog plasma decreases by 40% by spring in comparison with the values in autumn. More intensive proteolysis in lamprey tissues compared with that in frog tissues has been confirmed by quantitatively determining leucine, isoleucine, and valine in the blood of these animals. Besides these three amino acids, alanine, glycine, lysine, threonine and, in certain periods, tyrosine have been found to be quantitatively significant in the plasma of both animals.