Thrombin-induced inositol trisphosphate production by rabbit platelets is inhibited by ethanol

Abstract

Ethanol has an inhibitory effect on some platelet functions, but the mechanisms by which it exerts this effect are not known. Using suspensions of washed platelets, we observed that ethanol (1-9 mg/ml) did not affect the aggregation of rabbit platelets stimulated with ADP (0.5-10 microM). When platelets were prelabelled with 5-hydroxy[14C]tryptamine, aggregation and secretion of granule contents in response to thrombin (0.01-0.10 unit/ml) were not inhibited by ethanol, but these responses to thrombin at lower concentrations (less than 0.01 unit/ml) were inhibited by ethanol (2-4 mg/ml). Platelets were prelabelled with [3H]inositol so that increases in inositol phosphates upon stimulation could be assessed by measuring the amount of label in these compounds. ADP-induced increases in IP (inositol phosphate) and IP2 (inositol bisphosphate) were not affected by ethanol. IP3 (inositol trisphosphate) was not changed by ADP or ethanol. Although ethanol did not affect the increases in IP, IP2 and IP3 caused by stimulation of platelets with thrombin at concentrations greater than 0.01 unit/ml, ethanol did inhibit the increases observed at 2 and 3 min in these inositol phosphates caused by lower concentrations of thrombin (less than 0.01 unit/ml). Since ADP did not cause formation of IP3 in rabbit platelets, and since no thromboxane B2 was detected in platelets stimulated with the lower concentrations of thrombin, it is unlikely that the inhibitory effect of ethanol in IP3 formation was due to effects on further stimulation of platelets by released ADP or by thromboxane A2. Ethanol may inhibit platelet responses to thrombin by inhibiting the production of the second messenger, IP3.

Acute in vitro effects of ethanol on responses of platelets from cholesterol-fed and Watanabe heritable hyperlipidemic rabbits.

“…The analysis that we have performed of our data at equal extents of aggregation shows that ethanol was actually less inhibitory of thrombin-induced responses with platelets from the cholesterol-fed rabbits than with platelets from the control rabbits. Thus, although ethanol inhibits the activation or activity of phospholipase C in thrombin-stimulated platelets, 47 it may do so to a lesser extent in platelets from cholesterol-fed rabbits.…”

Effects of alcohols on responses evoked by inositol trisphosphate in Xenopus oocytes.

“…It is also consistent with findings that ethanol can evoke oscillatory Clcurrents in the oocyte (Wafford et al 1989), which almost certainly arise as a result of InsP3 formation, and that ethanol mobilizes Ca21 in hepatocytes by activation of phospholipase C (Hoek, Thomas, Rubin & Rubin, 1987). However, the contrary effect has been reported in platelets, where ethanol inhibits thrombinstimulated InsP3 formation (Rand, Vickers, Kinlough-Rathbone, Packham & Mustard, 1988). The depressant effects of ethanol and higher alcohols on InsP3-mediated Ca21 release presumably arise within the cell at, or close to, the sites of Ca2' release.…”

Alcohol and polyphenolic grape extract inhibit platelet adhesion in flowing blood

“…Addition of alcohol to platelets in vitro inhibits platelet aggregation by ADP, collagen, thrombin and platelet activating factor (PAF) [11][12][13][14]. Alcohol fails to change platelet shape but reduces the release of arachidonic acid, suggesting interference with phospholipase A 2 activity [11,12,[15][16][17].…”