THE MODULATION OF THE INCREASE IN RAT FACIAL SKIN BLOOD-FLOW OBSERVEDAFTER TRIGEMINAL GANGLION STIMULATION

Electrical stimulation of the trigeminal ganglion causes an increase i n facial skin blood flow in the anaesthetised rat, as measured by lase r Doppler flowmetry. We investigated the modulation of this neurogenic vasodilator response using selective receptor agonists for putative p rejunctional inhibitory receptors, as well as other pharmacological ag ents to further characterise this response. [D-Ala(2),Me-Phe(4),Gly(5) -ol]enkephalin (DAGO, a mu-opioid receptor agonist) inhibited the vaso dilator response in a dose-related (0.058-5.8 mu mol/kg i.v.) and nalo xone-sensitive manner. A similar inhibitory response was observed with the local anaesthetic lignocaine (2% w/v, s.c. 20 mu l) In contrast, the histamine H-3-receptor agonist mu-methylhistamine (15 or 35 mu mol /kg, i.v.) and the 5-HT1D receptor agonists sumatriptan (0.24 or 2.4 m u mol/kg, i.v.) and CP 122,288 (0.0003-3 mu mol/kg, i.v.) had no effec t on these responses. Similarly, atropine (1.5 mu mol/kg, i.v.) and in domethacin (28 mu mol/kg, i.v.) did not alter the vasodilatation obser ved in this model. In conclusion, only mu-opioid receptor activation a nd local anaesthetic had any inhibitory action on the neurogenic vasod ilatation observed in this model.