EFFECT OF DRUGS AND CATIONS ON ULTRASTRUCTURE AND 5-HYDROXYTRYPTAMINE CONTENT OF BLOOD PLATELETS

¹ Research Departmenl, F. Hoffmann-La Roche & Co. Ltd., Basle, Switzerland

The action of reserpine, the benzoquinohzine derivative Ro 4-1284 and ^DL- amphetamine, as well as of Na and K, on the 5-hydroxytryptamine (5-HT) content and the ultrastructure of isolated blood platelets of rabbits has been investigated. The drugs electyvely decrease the number of dense intracellular osmiopilic bodies previously described as storing 5-HT (5-HT organecehles). The diminution of these organdies parallels that of the 5-HT content as estimated by a spectrophotofluorimetrie procedure. Only with high drug concentrations does damage occur to the general ultrastructure (mitochondria, glycogen- and -granules). In buffers deficient in Na or K, the endogenous content of 5-HT decreases approximately parallel to the intensity of general ultrastructural alterations. It is concluded that reserpine, Ro 4-1284 and DL-amphetamine liberate 5-HT from platelets by a specific interference with special 5-HT-containing subcellular organdies. In buffers deficient in Na or K, however, 5-HT liberation occurs concomitantly with nonspecific damage to the ultrastructure of the platelets.