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The anti-fatigue effect of phosphoserine, L-serine and a mixture of sodium phosphate and L-serine has been studied in rats. Phosphoserine orally administered induced a statistically significant anti-fatigue effect in rats of both sexes submitted to a training test by rotarod, with 14 sessions in 3 days. Furthermore, phosphoserine was utilized better than the mixture of sodium phosphate and L-serine, whereas L-serine alone induced no effect. Therefore, the effect of phosphoserine seems to be due to the phosphoryl bond.

RNA and protein synthesis is noticeably depressed in the brain of swimming rats. Repeated oral administration of phosphothreonine, phosphoserine or arginine is susceptible of improving brain macromolecular synthesis. A parallel induction is observed on spermine and spermidine accumulation, particularly evident when arginine is used. The anti-fatigue effect of phosphorylated amino acids or arginine may be associated with the observed restoration of brain macromolecular synthesis via polyamine accumulation.

A cardiac stress was performed in the isolated perfused rabbit heart by means of four injections of 0.5 µg epinephrine in the coronary vessels. The endogenous (–)carnitine/acetyl(–)carnitine ratio was also determined. The two exogenous optical isomers of carnitine possess a different pharmacological behavior on the epinephrine-induced stress. Exogenous (–)carnitine reduces the epinephrine stimulating effect whereas exogenous (+)carnitine increases it, including coronary flow. Furthermore, the endogenous (–)carnitine/acetyl(–)carnitine ratio decreases significantly by ssthe stress. Exogenous (–)carnitine restores this ratio to the normal value, whereas exogenous (+)carnitine does not. It is concluded that carnitine might represent an important natural way for organism safeguard in the epinephrine stress as occurs in various emotional states. In this respect the importance of exogenous (–)carnitine as a therapeutic means remains to be investigated