The effects of hyperthermia on polyribosomes and amino acid levels in infant rat brain

Brain polyribosomes prepared from infant rats exposed to elevated ambient temperatures (39.5°C for 45 min) are highly disaggregated. Disaggregation is evident 15 min after the animals have entered the hot environment and is nearly maximal after 25 min. Substantial recovery of polyribosomes is seen 20 min after the hyperthermic rats are transferred from 39.5 to 33°C ambient temperature, indicating that heat-induced disaggregation is quickly reversible. During hyperthermia the levels of certain amino acids in the brain, particularly essential amino acids, rise markedly. The increases in amino acid levels are reversed within 1 h after the rats are transferred from the hot environment to 33°C ambient temperature. The levels of amino acids in blood plasma also rise during hyperthermia; however, the increases are relatively smaller and less selective than in the brain but are also reversed by returning the animals to 33°C ambient temperature.Injection of phenylalanine into infant rats causes hyperphenylalaninemia, elevated brain phenylalanine levels, and brain polyribosome disaggregation (Aoki & Siegel, 1970). The present observations show that elevated brain amino acid levels and polyribosome disaggregation are also linked in hyperthermic infant rats, but it is not yet clear if the two phenomena are causally related. Although the mechanisms of the increases of blood and brain amino acid levels remain to be elucidated, they may have a significant bearing on the functional status of the protein synthetic machinery of the brain, on the levels of neurotransmitter substances in the brain which are derived from amino acid precursors, and on the intermediary metabolism of the brain.