Abstract
Previous data have shown both in the rat and in the human that a single mandibular extension lasting 10 min induces a significant important and prolonged reduction in blood pressure and heart rate, affecting also rat pial microcirculation by the release of endothelial factors. In the present work, we assessed whether repeated mandibular extension could further prolong these effects. We performed two mandibular extensions, the second mandibular extension being applied 10 min after the first one. The second mandibular extension produced a reduction in blood pressure and heart rate for at least 240 min. As in the case of a single mandibular extension, pial arterioles dilated persisting up to 140 min after the second extension. Spectral analysis on 30 min recordings under baseline conditions and after repetitive mandibular extensions showed that the pial arterioles dilation was associated with rhythmic diameter changes sustained by an increase in the frequency components related to endothelial, neurogenic, and myogenic activity while a single mandibular extension caused, conversely, an increase only in the endothelial activity. In conclusion, repetitive mandibular extension prolonged the effects of a single mandibular extension on blood pressure, heart rate and vasodilation and induced a modulation of different frequency components responsible of the pial arteriolar tone, in particular increasing the endothelial activity.
Highlights
A single mandibular extension (ME), consisting in a submaximal mouth opening for 10 min induced with an ad hoc dilator, has been shown to cause an unusually prolonged reduction of heart rate (HR) and mean arterial blood pressure (MABP) (Lapi et al, 2013, 2014) in normotensive anesthetized rats
The aim of the present study was twofold: on one hand to clarify if the cardiovascular effects could be prolonged when two mandibular extensions were applied; on the other hand to analyze the rhythmic oscillations of the rat pial arterioles diameter after ME because the changes of the smaller arterioles tone are the basis of the blood flow regulation to the tissue
In the rats treated with L-NIO, the spectral analysis carried out on recordings acquired between 120 and 150 min after ME (Figure 5A2) showed some significant changes of the frequency components: ULF was significantly increased [F(2, 14) = 72.06, p < 0.01 vs. baseline] while VLF was abolished compared with the baseline conditions (Figure 5A1); ILF and HF frequency components significantly increased compared with the baseline conditions [F(2, 14) = 37.09, p < 0.01; F(2, 14) = 371, p < 0.01 vs. baseline, respectively] and VHF frequency component significantly decreased [F(2, 14) = 108, p < 0.01 vs. baseline] while LF frequency component did not change (Figure 5A2)
Summary
A single mandibular extension (ME), consisting in a submaximal mouth opening for 10 min induced with an ad hoc dilator, has been shown to cause an unusually prolonged reduction (of almost 3 h) of heart rate (HR) and mean arterial blood pressure (MABP) (Lapi et al, 2013, 2014) in normotensive anesthetized rats. The hypotensive and bradycardic effects have been found to be associated to a characteristic biphasic response of the pial arteriolar diameters, consisting in an initial brief vasoconstriction concomitant with ME followed by a prolonged vasodilation lasting for the whole experimental observation period of 3 h. The effects are depend on the ME duration, 10 min ME resulting the optimal stimulus (Lapi et al, 2013). The initial brief vasoconstrictory response involves an opioid receptor-mediated mechanism, and the subsequent prolonged vasodilation is related to NO intracellular signaling (Lapi et al, 2014)
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