THROM8OSISRESEARCH22; 525-533,1981 0049-3848,!81/110525-09$02.00/O Printed in the USA. Copyright (c) 1981 PergamonPress Ltd. All rights reserved. EVIDENCE FOR THE INVOLVEMENT OF MICROTUBULES IN THE ADP-INDUCED SECRETION OF PLATELET 14C-5-HYDROXYTRYPTAMINE J.F. Martin*, T.K. Holland and R.G.G. Russell Department of Human Metabolism and Clinical Biochemistry. University of Sheffield Medical School, Sheffield, SlO 2RX, England and *Department of Medicine, St. Vincent's Hospital University of Melbourne, Australia. (Received 30.1.1981; in revisedform 1.4.1981. Acceptedby Editor P.A. Castaldi) ABSTRACT Platelet rich plasma was incubated with either saline or vincristine. Transmission electromicroscopy showed microtubules to be present in saline preincubated platelets, but absent from the platI$lets preincubated with vincristine. The release of C labelled 5-Hydra. xytryptamine (5HT) by adenosine diphosphate (ADP) was inhibited in the vincristine treated platelets, although ADP induced aggregation was similar in the vincristine and saline treated platelets. It is con- cluded that microtubules have a role in ADP induced secertion of 5HT, but not in ADP induced aggregation. INTRODUCTION Stimulation of platelets by ADP, adrenaline, collagen or thrombin causes selective secretion of the contents of storage organelles (l-4). Several types of storage organelles are found in the platelet (4) although the secretion of their contents may be divided into two categories. The rapid secretion of dense granule contents, namely ADP, ATP, pyrophos phate, calcium and 5-hydroxytryptamine has been designated release I, whilst the slower secretion of a heterogenous popul- KEYWORDS: Microtubules. ation, adenosine vincristine. platelet secretion, platelet aggreg- diphosphate, 5_hydroxytryptamine, 525