Antidromic vasodilatation in the rat hindpaw measured by laser Doppler flowmetry: pharmacological modulation.

Antidromic vasodilatation in the hindpaw skin of rats was studied by laser Doppler flowmetry (LDF). Antidromic stimulation of the saphenous nerve (10 V, 1 ms, 2 Hz, 15 s) increased LDF readings more than two-fold. This increase was abolished by acute nerve section, local lidocain or local 1% capsaicin, augmented by guanethidine (20 mg/kg) and unaffected by atropine (1 mg/kg). While mepyramine plus cimetidine (10 mg/kg each) reduced basal LDF readings, they did not change the percent increase after stimulation. [D-Met2, Pro5] enkephalinamide (3 mg/kg) caused a naloxone-reversible inhibition of the stimulation-induced increase. Lofentanil (10 micrograms/kg i.v.) also caused an inhibition but this was associated with a marked fall in blood pressure. These results indicate that LDF is a suitable non-invasive method for the indirect measurement of antidromic vasodilatation in rat skin. While opiates appear to inhibit the release of the neurogenic vasoactive mediator(s), histamine is unlikely to be involved in the rapid vasodilator response following antidromic sensory nerve stimulation.