Suppression of amphetamine-induced hypothermia by the neutral amino acid valine.

Pretreatment with valine (0.5-2.0 mmoles/kg) can suppress the hypothermic response of rats placed in a 4degreesC environment and given d-amphetamine sulfate (5 or 10 mg/kg). The amino acid was most effective when given 30 minutes before amphetamine administration, at which time it also significantly lowered brain tyrosine concentration (and, presumably, suppressed catecholamine synthesis). Because dopaminergic neurons mediate the hypothermic response to amphetamine and because amphetamine's ability to produce hypothermia requires, in part, the release of newly synthesized dopamine, these observed effects of valine pretreatment support the hypothesis that treatments which alter precursor (tyrosine) availability also affect brain catecholamine synthesis.