Investigation into the mechanisms by which nedocromil sodium, frusemide and bumetanide inhibit the histamine-induced itch and flare response in human skin in vivo.
BACKGROUND
In a previous study, iontophoresis of nedocromil sodium into human skin in vivo was shown to reduce histamine-induced itch and flare. In asthma, the Na+/K+/2Cl- cotransporter inhibitors, frusemide and bumetanide, have been reported to have many similar actions to nedocromil sodium.


OBJECTIVE
To compare the effects of these drugs in the histamine-induced itch, flare and weal response in human skin in vivo and elucidate their site of action.


METHODS
Nedocromil sodium, frusemide bumetanide and reversed osmosis water (control), were introduced by iontophoresis into the forearm skin of 10 volunteers in each of two single-blind studies. In study 1, histamine (20 microL of 100 microM) or vehicle was injected into the area of iontophoresis 10 min later. In study 2, histamine or vehicle was injected 5 mm outside the area of iontophoresis so the flare developed over the area of iontophoresis. Itch was scored on a visual analogue scale every 20 s for 5 min, flare areas were assessed using scanning laser Doppler imaging up to 10 min and weal was assessed by planimetry at 10 min.


RESULTS
In study 1, nedocromil sodium, frusemide and bumetanide reduced itch scores by 36%, 48% and 34%, respectively, and flare areas by 17%, 26% and 15% respectively (all P<0.05). Weal areas and blood flux in the flare were unaffected. In study 2, itch scores, flare areas and weal areas were not inhibited. Also, blood flux values in areas of drug and water iontophoresis were not different.


CONCLUSIONS
This study has provided evidence to support the hypothesis that nedocromil sodium, frusemide and bumetanide inhibit sensory nerve activation to reduce the itch and flare responses induced by histamine in human skin in vivo. It is likely that inhibition of a Na+/K+/2Cl- cotransporter in the sensory nerve membrane is a possible mechanism of action.
Division of Infection, Inflammation and Repair, School of Medicine, University of Southampton, Southampton, UK.
E F
EF
Willis
G F
GF
Clough
M K
MK
Church
D000328:Adult; D002034:Bumetanide / Q000627:therapeutic use; D005665:Furosemide / Q000627:therapeutic use; D017950:Ganglia, Sensory / Q000187:drug effects; D006632:Histamine / Q000494:pharmacology; D006634:Histamine H1 Antagonists / Q000627:therapeutic use*; D006801:Humans; D007478:Iontophoresis; D017078:Laser-Doppler Flowmetry; D017835:Nedocromil / Q000627:therapeutic use*; D016037:Single-Blind Method; D012867:Skin / Q000098:blood supply / Q000294:innervation; D014581:Urticaria / Q000188:drug therapy* / Q000503:physiopathology; D014664:Vasodilation / Q000187:drug effects
D006634:Histamine H1 Antagonists; D017835:Nedocromil; D002034:Bumetanide; D005665:Furosemide; D006632:Histamine