Trigeminal nerve-mediated reflex arterial blood pressure decrease and vasodilatation in lower lip of the rabbit

We measured the effects of electrical stimulation of the central cut end of the lingual nerve on lower lip blood flow (LBF) and on arterial blood pressure in urethane-anesthetized, artificially ventilated, cervically vagosympathectomized rabbits. Different effects were observed depending on the stimulus frequency. Increasing the stimulus frequency above 5 Hz produced progressively larger ipsilateral LBF increases until the optimal frequency was reached at 20 Hz. In contrast, stimulation at above 0.5 Hz evoked progressively larger decreases in both contralateral LBF and arterial blood pressure until the optimal frequency was reached at around 10 and 2 Hz, respectively. Thus, the optimal stimulus frequencies for the ipsilateral LBF increase and the arterial blood pressure decrease were widely different. The lingual nerve-evoked change (i.e., fall) in arterial blood pressure showed a significant correlation with the contralateral LBF decrease, but not with the ipsilateral LBF increase. Prior administration of hexamethonium at 10 mg/kg markedly reduced both the ipsilateral LBF increase and arterial blood pressure decrease, although it was more effective against the former than against the latter. Pretreatment with scopolamine (muscarinic-receptor antagonist, 0.1 mg/kg), phentolamine (α-adrenoceptor antagonist, 0.1 mg/kg), or propranolol (β-adrenoceptor antagonist, 0.1 mg/kg) failed to affect either response. However, 1.0 mg/kg phentolamine significantly reduced both responses (P<0.05). These results indicate that, in the rabbit, the LN-evoked reflex increase in ipsilateral LBF is (a) largely independent of any concomitant arterial blood pressure change and (b) probably due to active vasodilatation mediated via parasympathetic mechanisms. In contrast, the evoked decrease in contralateral LBF was proportional to the decrease in arterial blood pressure, suggesting that the former was secondary to the latter.