Oral single high-dose aspirin results in a long-lived inhibition of anodal current-induced vasodilatation

Abstract

1 Acetyl salicyclic acid (aspirin) irreversibly blocks cyclo-oxygenase (COX). This effect is short-lived in endothelial or smooth muscle cells due to resynthesis but long-lived in platelets devoid of synthesis ability. Aspirin blocks the anodal current-induced vasodilatation, suggesting participation by prostaglandin (PG). We analysed the time course of the effect of aspirin as an indirect indicator of the origin of the PG possibly involved in anodal current-induced vasodilatation. 2 In healthy volunteers, vasodilatation, estimated from the peak cutaneous vascular conductance (CVC(peak)), was recorded in the forearm during and in the 20 min following 5 min, 0.10 mA transcutaneous anodal current application, using deionized water as a vehicle. CVC(peak) was normalized to 44 degrees C heat-induced maximal vasodilatation and expressed in per cent values. Experiments were performed before and at 2 and 10 h, 3, 7, 10 and 14 days after blinded 1-g aspirin or placebo treatment. 3 CVC(peak) (mean+/-s.d.mean) after aspirin vs placebo was 13.6+/-14.5 vs 65.0+/-32.1 (P<0.05) 14.7+/-4.2 vs 87.5+/-31.9 (P<0.05), 18.1+/-10.2 vs 71.6+/-26.8 (P<0.05), 42.5+/-23.4 vs 73.3+/-26.8 (non significant, NS), 60.2+/-24.3 vs 75.2+/-26.9 (NS), 52.1+/-18.5 vs 67.9+/-32.1 (NS) at 2 and 10 h and at days 3, 7, 10 and 14 respectively. 4 Aspirin inhibition of anodal current-induced vasodilatation persists long after endothelial and smooth muscle cyclo-oxygenases are assumed to be restored. This suggests that the PG involved in this response are not endothelial- or smooth muscle-derived. The underlying mechanism of this unexpected long-lived inhibition of vasodilatation by single high dose aspirin remains to be studied.

Figure 1

Example of the time course of the cutaneous vascular conductance, expressed as per cent of maximal heat-induced vasodilatation in one typical subject in the pretreatment experiment, at 2 h and at days 3, 7 and 14 following aspirin or placebo treatment. Grey bar schematizes the 5 min application of anodal 100 μA continuous application. Hashed bar is the period of local 44°C heating.

Figure 2

Mean cutaneous blood flow response±s.e.mean (estimated from cutaneous vascular conductance (CVC)) observed in the 2 min preceding, during and in the 20 min following a 5-min anodal current application, at different intervals from aspirin (right graphs) or placebo (left graphs) treatment: 2 and 10 h and at day 3, 7, 10 and 14. Results are expressed as per cent of maximal heat-induced CVC (% CVC_max). The heating period is not presented to simplify the graph.

Figure 3

Time course evolution of the ratios of mean CVC_peak and mean CVC₂₀ to mean CVC_rest in response to 5 min monopolar anodal current application before, at 2 and 10 h and at days 3, 7, 10 and 14 following 1-g single oral dose aspirin treatment. The dashed line represents the ratio of 1 for which no change is found from CVC_rest.