Spontaneous efflux of platelet alpha-granule components in relation to 14C-norepinephrine in buffers

In an investigation of the spontaneous efflux of beta-thromboglobulin (beta-TG), 14C-norepinephrine (14C-NE) and growth stimulating activity (GSA), measured as incorporation of 3H-thymidine in rabbit aortic smooth cells, from platelets resuspended in Ca++- and Mg++-free buffer a continuous increase in 3H-thymidine incorporation was seen during 120 min. There was good stoichiometric parallelism between beta-TG and 14C-NE during the 80 minutes the experiment lasted, indicating that norepinephrine is incorporated in alpha-granules and release by exocytosis.