THE EFFECTS OF DRUGS ON THE UPTAKE OF AMINES BY MAST CELLS

Neoplastic mast cells, taken from an ascitic tumour in mice and incubated in vitro, took up (14)C-labelled 5-hydroxytryptamine and histamine from the medium. Uptake during the first hour gave an approximate measure of the initial rate. The amount of each amine taken up in this time was determined by bioassay and by radioactivity, the two methods giving similar results. The curves obtained by plotting initial rate of uptake against concentration in the medium suggested that the uptake of 5-hydroxytryptamine was by an active process and also by diffusion, whereas uptake of histamine was by diffusion only. The cells also took up (14)C-labelled (+/-)-noradrenaline and tryptamine, apparently by diffusion. The active uptake of 5-hydroxytryptamine was inhibited by lowering the temperature to 25 degrees C or by increasing the pH to 8.9, procedures which had little effect on histamine uptake. The effects of cocaine, imipramine, chlorpromazine, mepyramine, promethazine, phenoxybenzamine, lysergic acid diethylamide, bromolysergic acid diethylamide, methysergide, guanethidine, dichloroisoprenaline and pronethalol on the uptake of amines were examined. In general, any antagonist which inhibited uptake of 5-hydroxytryptamine had little effect on uptake of histamine, and vice versa. Possible ways in which these antagonists produce their effects on amine uptake are discussed. A high concentration of 5-hydroxytryptamine, of tryptamine or of noradrenaline inhibited uptake of histamine, but only tryptamine decreased uptake of 5-hydroxytryptamine. These results, together with those from experiments with antagonists, suggest that there are specific binding sites for 5-hydroxtryptamine in these cells.

A COMPARISON OF PLATELET AGGREGATION PRODUCED BY SEVEN COMPOUNDS AND A COMPARISON OF THEIR INHIBITORS

The aggregating effects of adenosine diphosphate, thrombin, 5-hydroxytryptamine, tryptamine, adrenaline and noradrenaline, and tri-ethyl tin have been carefully compared. The first three compounds in some circumstances produce remarkably similar effects although there are important differences. The kinetics of aggregation induced by adrenaline (and noradrenaline) are quite different and the tri-ethyl tin effects are different again. Anti-serotonins specifically inhibit 5-hydroxytryptamine and the anti-adrenaline drug phentolamine specifically inhibits the effects of the catecholamines. Experiments presented suggest but do not prove that aggregation produced by all these compounds is accompanied by the liberation of diphosphate from the platelets and that platelet triphosphate may be converted to diphosphate. How these different compounds all produce this effect is discussed. Either the presence of diphosphate or the action of a triphosphatase might be the immediate cause of aggregation if there is a single final common cause. The anti-adrenaline phentolamine prolongs the bleeding time, so adrenaline or noradrenaline may be involved in platelet phenomena in haemostasis.