Abstract
Estimation of dopamine (DA) synthesis in the rat striatum was performed by measuring, as a function of time, both the 3H-H2O which was formed as a result of L-3,5-3H-tyrosine . hydroxylation to 3H-dopa, and 3H-DA accumulation. Striatal slices were incubated for various time periods up to 30 minutes with L-3,5-3H-tyrosine and the "total" 3H-H2O and 3H-DA accumulated in slices and incubating medium were measured. The rate of 3H-H2O formation paralleled the rate of 3H-DA accumulation in normal rats indicating that 3H-DA newly synthesized is protected from enzymatic inactivation. α-Methyl-p-tyrosine inhibited similarly 3H-H2O and 3H-DA accumulation. Reserpine pretreatment inhibited storage as well as synthesis of DA; 3H-DA and 3H-H2O accumulation were diminished by 70% and 35%, respectively. In striatal slices of rats pretreated with a neuroleptic, thioproperazin, 3H-H2O and 3H-DA accumulation were both increased by 70%. On the other hand, amphetamine administered in vivo or in vitro decreased both 3H-H2O and 3H-DA (40%). Initial rates of DA synthesis were estimated for increasing concentrations of l-3,5-3H tyrosine in the incubating medium. Km and Vmax for DA synthesis in striatal slices of normal and amphetamine-pretreated rats were determined by graphic analysis with the method of Lineweaver and Burk. This kinetic analysis revealed that amphetamine inhibited DA synthesis by noncompetitive inhibition for tyrosine. This study demonstrated that changes in biosynthetic regulation of DA in the striatum induced by psychotropic drugs can be estimated accurately and distinguished from effects on other DA metabolic processes.
Footnotes
- Received July 6, 1970.
- Accepted November 28, 1970.
- © 1971, by The Williams & Wilkins Company
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