INTRODUCTION: Laser-Doppler flowmetry (LDF) coupled with acetylcholine chloride (ACh) iontophoresis is increasingly recognized as a reliable non-invasive method to study the endothelial function. However, ACh-vasodilation measurement appears highly variable possibly due to the ACh pharmacological properties itself. These problems may be partially overcome by using methacholine chloride (MCh), a more stable synthetic agonist of muscarinic receptors, instead of ACh. Therefore, we first studied the correlation between the two drugs and then the effects of (1) spatial variability (inter-site measurements), (2) temporal variability (inter-day measurements), (3) intra-day variability (morning versus evening), and (4) age on the variability of both ACh-vasodilation and MCh-vasodilation. METHODS: The endothelium-dependent vasodilation response to simultaneous iontophoretic applications (4 doses of 10s at 0.1mA with 2min of current-free interval) of ACh (11mM) or MCh (10mM) was studied on the forearm of 40 healthy subjects (36 males, median 28yr, range 21-59yr). The percent change in perfusion (CVCpeak) from baseline and the area under the curve (CVC(AUC)) during iontophoresis were assessed. Inter-site, inter-day and intra-day coefficients of variation (CV) were studied for each drug as well as correlations between drugs and age. RESULTS: A linear relationship was found between ACh- and MCh-CVCpeak (r²=0.75, p=0.01) and between ACh- and MCh-CVC(AUC) (r²=0.55, p=0.02). MCh inter-site CV for both CVCpeak (12.2%) and CVC(AUC) (13.8%) was significantly lower than ACh inter-site CV for CVCpeak (15.5%) and CVC(AUC) (15.3%), respectively. MCh inter-day CV for CVCpeak (17.2%) and CVC(AUC) (14.6%) was significantly lower than ACh inter-day CV for CVCpeak (19.7%) and ACh CVC(AUC) (21.2%). For ACh and MCh, the CVCpeak and CVC(AUC) were higher at 16:00pm than at 11:00am (p<0.05 for all). Finally, both ACh- and MCh-CVCpeak exhibited a logarithmic decrease with age (r²=0.61, p<0.01 and r²=0.58, p<0.01). CONCLUSION: Although both drugs exhibited circadian and age variability, MCh exhibited less inter-site and interday variabilities than did ACh for the evaluation of cutaneous endothelium-dependent vasodilation. These findings should be taken into account in studies of cutaneous vascular function by iontophoresis coupled with laser Doppler flowmetry.
INTRODUCTION: Laser-Doppler flowmetry (LDF) coupled with acetylcholine chloride (ACh) iontophoresis is increasingly recognized as a reliable non-invasive method to study the endothelial function. However, ACh-vasodilation measurement appears highly variable possibly due to the ACh pharmacological properties itself. These problems may be partially overcome by using methacholine chloride (MCh), a more stable synthetic agonist of muscarinic receptors, instead of ACh. Therefore, we first studied the correlation between the two drugs and then the effects of (1) spatial variability (inter-site measurements), (2) temporal variability (inter-day measurements), (3) intra-day variability (morning versus evening), and (4) age on the variability of both ACh-vasodilation and MCh-vasodilation. METHODS: The endothelium-dependent vasodilation response to simultaneous iontophoretic applications (4 doses of 10s at 0.1mA with 2min of current-free interval) of ACh (11mM) or MCh (10mM) was studied on the forearm of 40 healthy subjects (36 males, median 28yr, range 21-59yr). The percent change in perfusion (CVCpeak) from baseline and the area under the curve (CVC(AUC)) during iontophoresis were assessed. Inter-site, inter-day and intra-day coefficients of variation (CV) were studied for each drug as well as correlations between drugs and age. RESULTS: A linear relationship was found between ACh- and MCh-CVCpeak (r²=0.75, p=0.01) and between ACh- and MCh-CVC(AUC) (r²=0.55, p=0.02). MCh inter-site CV for both CVCpeak (12.2%) and CVC(AUC) (13.8%) was significantly lower than ACh inter-site CV for CVCpeak (15.5%) and CVC(AUC) (15.3%), respectively. MCh inter-day CV for CVCpeak (17.2%) and CVC(AUC) (14.6%) was significantly lower than ACh inter-day CV for CVCpeak (19.7%) and ACh CVC(AUC) (21.2%). For ACh and MCh, the CVCpeak and CVC(AUC) were higher at 16:00pm than at 11:00am (p<0.05 for all). Finally, both ACh- and MCh-CVCpeak exhibited a logarithmic decrease with age (r²=0.61, p<0.01 and r²=0.58, p<0.01). CONCLUSION: Although both drugs exhibited circadian and age variability, MCh exhibited less inter-site and interday variabilities than did ACh for the evaluation of cutaneous endothelium-dependent vasodilation. These findings should be taken into account in studies of cutaneous vascular function by iontophoresis coupled with laser Doppler flowmetry.