EVIDENCE OF A LOCAL MECHANISM FOR DESMOPRESSIN-INDUCED TISSUE-TYPE PLASMINOGEN-ACTIVATOR RELEASE IN HUMAN FOREARM

Systemic administration of desmopressin (DDAVP) induces increased plas ma levels of tissue-type plasminogen activator (t-PA), coagulation fac tor VIII, and von Willebrand factor (VWF). However, the mechanisms beh ind these responses are not known. We tested the hypothesis that DDAVP acts as a local stimulator of acute endothelial release of t-PA and v WF independently of central pathways. Healthy, young, nonsmoking male volunteers were studied. In a first study (n = 7), DDAVP and placebo w ere administered as randomized single-blind stepwise intrabrachial art ery infusions (0.7, 7.0, and 70 ng/min). In a another subset of subjec ts (n = 4), a constant-rate DDAVP infusion of 70 ng/min was administer ed for 20 minutes in the brachial artery of the nondominant arm with t he dominant arm as control. To rule out that the observed t-PA release was flow-dependent, 4 additional subjects received stepwise intra-art erial infusions of both DDAVP (7.0, 21, and 70 ng/min) and sodium nitr oprusside (SNP; 0.5, 2.5, and 10 mu g/min). Brachial venoarterial plas ma concentration gradients and forearm plasma flow were used to determ ine net release/uptake rates of t-PA and vWF. At baseline, the average net release rate of t-PA was 6.7 ng/min across the whole forearm vasc ular bed, whereas there was no detectable basal release of vWF. Stepwi se infusion of DDAVP induced a massive regulated release of t-PA with a peak after 15 minutes on the highest dose-step (ANOVA; P < .0001). T he average maximum net release rate was 178 ng/min, and the total amou nt of t-PA released was, on the average, 3,000 ng. The majority was re leased in its active form. Constant-rate DDAVP infusion again markedly increased t-PA release in the infusion arm but had no effect whatsoev er in the control arm. In contrast, DDAVP did not stimulate a local re lease of vWF in either study. Central hemodynamics were unchanged duri ng infusions despite a local vasodilatory response with DDAVP. Endothe lium-independent flow stimulation by SNP did not elicit any local t-PA release. We conclude that DDAVP induces a massive acute flow-independ ent release of t-PA, without the simultaneous release of vWF, in the h uman forearm vascular bed. The lack of a t-PA response in the control arm, as well as the unaltered central hemodynamics with DDAVP, confirm s that the observed regulated t-PA release is local and independent of central mechanisms. (C) 1998 by The American Society of Hematology.