Secondary Metabolites and Aspartic Acid in the Brain of the Frog Rana temporaria as Low-Temperature Adaptogens

Abstract

Previously, we have demonstrated that such secondary metabolites as phosphoethanolamine (PE) and phosphoserine (PS) are low-temperature adaptogens specific to the brain of freshwater fish, in contrast to taurine which serves as an adaptogen in fish muscles and blood plasma. Here, we carry on investigating the role of PE, PS, taurine and proteinogenic amino acids in adaptation of poikilothermic animals to low temperatures. PE and PS were discovered in the brain of the frog Rana temporaria, and their pools were shown to increase by the onset of hibernation compared to the summer period almost in a similar manner (PE—from 0.22 to 1.65, PS—from 0.29 to 1.98 µmol/g wet weight). Unlike the fish brain, in the R. temporaria brain, the PE/PS ratio was almost indistinguishable in the winter compared to the summer. In contrast to fish, in the R. temporaria brain, the taurine level increased from 0.77 µmol/g in the summer to 1.37 µmol/g in the winter. The level of aspartic acid, which was missing in the fish brain during the winter, in the R. temporaria brain sharply increased by the onset of hibernation from 0.86 to 4.60 µmol/g. Thus, there is ground to believe that such secondary metabolites as PE, PS, taurine and proteinogenic aspartic acid play the role of low-temperature adaptogens in the brain of anuran amphibians.