Skin blood flow responses to the iontophoresis of acetylcholine and sodium nitroprusside in man: possible mechanisms

• Published in: The Journal of physiology Vol. 496; no. Pt 2; pp. 531 - 542
• Main Authors: Morris, S J, Shore, A C
• Format: Journal Article
• Language: English
• Published: England The Physiological Society 15-10-1996
• Subjects: Acetylcholine - administration & dosage; Acetylcholine - pharmacology; Adult; Citrus; Cyclooxygenase Inhibitors - pharmacology; Double-Blind Method; Electric Stimulation; Erythrocytes - physiology; Female; Humans; Iontophoresis; Laser-Doppler Flowmetry; Male; Neurons, Afferent - drug effects; Neurons, Afferent - physiology; Nitroprusside - administration & dosage; Nitroprusside - pharmacology; Prostaglandins - biosynthesis; Prostaglandins - physiology; Regional Blood Flow - drug effects; Regional Blood Flow - physiology; Reproducibility of Results; Skin - blood supply; Skin - drug effects; Skin - innervation; Vasodilation - drug effects; Vasodilation - physiology; Vasodilator Agents - administration & dosage; Vasodilator Agents - pharmacology
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.1996.sp021704

1. The mechanisms involved in the human skin blood flow responses to iontophoretic application of acetylcholine (ACH; delivered
using an anodal charge) or sodium nitroprusside (SNP; administered with a cathodal charge) are unclear. The aims of this study
were to investigate possible contributions of prostaglandin production to the increase in skin blood flow induced following
the iontophoresis of ACh and to investigate possible contributions from local sensory nerves to the perfusion responses induced
by ACh, SNP and their vehicles. 2. The contribution of prostaglandins to the ACh response was determined in a randomized double-blind
study of eight healthy subjects, who were studied on two occasions. Basal responses to ACh were measured before the oral administration
of 600 mg soluble aspirin in diluted orange juice (1 occasion or orange juice (1 occasion) and again 30 min after the drink.
The contribution of local sensory nerve activation to the responses to ACh and ACh vehicle (8 subjects) and to SNP and SNP
vehicle (7 subjects) was assessed. EMLA (5%) (a eutectic mixture of lignocaine and prilocaine) and placebo cream were applied
to two separate areas on the forearm in a double-blind randomized manner 2 h before drug responses were measured. In all studies
the skin microcirculation responses to iontophoretically applied drug vehicle (1 site) and drug (2 sites) were recorded by
laser Doppler perfusion imaging. 3. The increase in forearm skin perfusion (P < 0.001) in response to the iontophoresis of
ACh minus the response to ACh vehicle was not significantly different following placebo or aspirin administration. The increase
in forearm skin red blood cell flux (P < 0.001) in response to the iontophoresis of ACh minus the response to ACh vehicle
was not significantly different at the placebo-compared with the EMLA-treated site. THe small increase in perfusion (P < 0.001)
in response to the iontophoresis of ACh vehicle was significantly inhibited at the EMLA-compared with the placebo-treated
site (P < 0.05). The marked increase in perfusion (P < 0.001) in response to the iontophoresis of SNP vehicle was significantly
inhibited at the EMLA-compared with the placebo-treated site (P < 0.01). 4. These data suggest that in healthy volunteers:
(1) mechanisms other than prostaglandin production and local sensory nerve activation may be involved in the increase in skin
perfusion observed following the iontophoretic application of ACh; and (2) stimulation of local sensory nerves may be responsible
for the increase in tissue perfusion observed following the iontophoretic application of either ACh vehicle or SNP vehicle.