Attempts to isolate the putative endogenous ligand for the benzodiazepine receptor from bovine urine resulted in the identification of three isoflavans: equol (1), 3',7-dihydroxyisoflavan (2), and 4'-hydroxy-7-methoxyisoflavan (9), as "diazepam-like" compounds. 3-Chloro-9H-carbazole (17) was found to enhance the binding of diazepam in the benzodiazepine receptor binding assay. Pinosylvine monomethyl ether (18), indigo (20), and indirubin (21) were isolated as inactive compounds.

Human blood platelets incubated for one hour at 37° C. with dopamine-l-HC (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 f3-hydroxylase.

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Effects of debrisoquin on the human platelet have been characterized in vivo and in vitro.The drug inhibits the uptake of serotonin by competing for a common transport process, interferes with the storage of serotonin within this cell, and inhibits platelet monoamine oxidase (MAO) activity. Similarities between the platelet and adrenergic neuron suggest that the platelet may serve as a convenient model for the neuron.

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