Platelet MAO Research Articles

The accumulation and metabolism of dopamine by the human platelet

Human blood platelets incubated for one hour at 37° C. with dopamine‐l‐14C (DA) accumulated the amine against a gradient. Such accumulation was markedly reduced by cold and by various metabolic inhibitors including iodoacetate, dinitrophenol, and sodium cyanide. Increasing the concentration of DA caused a decrease in the steady‐state distribution ratio which suggests that the uptake process is saturable. Various compounds which inhibit or compete for the amine pump in the platelet membrane, including desmethylimpromine (DMI), diphenhydramine, serotonin, debrisoquin, and guanethidine, depress the accumulation of DA. Uptake of DA was also reduced by benztropine, trihexyphenidyl, and haloperidol. Less than 10 per cent of the DA which accumulates in the platelet during one hour is metabolized. DA is a relatively poor substrate for platelet MAO and in addition the cell does not appear to contain dopamine β‐hydroxylase.