Abstract
Previous studies in anesthetized normotensive rats demonstrated that a single mouth opening for 10 min obtained by an ad hoc dilator (mandibular extension [ME]) produced a blood pressure reduction by about 20 mmHg lasting for about 2 h and that once‐repeated ME prolonged this effect. We here describe these effects in hypertensive rats. Mean (intra) arterial blood pressure (MABP) and heart rate (HR) was followed for up to a maximum of 470 min after single or repeated 10 min‐lasting ME in two groups of anesthetized, male, 6–9 months old hypertensive rats. In one group, hypertension was induced by dexamethasone (20 μg/kg/day, subcutaneously for 7 days; Dex‐HT); the other group was spontaneously hypertensive rats (SHR). Studies were done, in Dex‐HT rats, after only surgical procedures (no ME, sham‐operated rats), single ME, early repeated (after 10 min) ME (ER‐ME) and late repeated (after 160 min) ME (LR‐ME) and, in SHR, after only surgical procedures and ER‐ME. One‐way ANOVA for repeated measures revealed no significant effect on MABP and HR in sham‐operated groups. In Dex‐HT rats, single ME was followed by a significant MABP decline by 25 mmHg, lasting for 100 min; ER‐ME and LR‐ME were followed by an even greater significant MABP decline by 40 mmHg, which outlasted the experimental observation period. In SHR, ER‐ME gave similar results as in Dex‐HT rats. HR significantly declined in all, except sham‐operated groups. In conclusions, ME is followed by a prolonged MABP decline also in hypertensive rats. This effect is even more pronounced, in length and magnitude, after repeated ME.
Highlights
Several evidence indicate that manipulations in the facial region can induce autonomic reflexes that result in blood pressure (BP) and heart rate (HR) reduction in both animals (Kumada et al 1977) and humans (Cornelius et al 2010; Schaller et al 2009)
Previous studies in anesthetized normotensive rats demonstrated that a single mouth opening for 10 min obtained by an ad hoc dilator produced a blood pressure reduction by about 20 mmHg lasting for about 2 h and that once-repeated mandibular extension (ME) prolonged this effect
The time course of Mean (intra) arterial blood pressure (MABP) and HR in the four study groups is reported in Figures 2 and 3
Summary
Several evidence indicate that manipulations in the facial region can induce autonomic reflexes that result in blood pressure (BP) and heart rate (HR) reduction in both animals (Kumada et al 1977) and humans (Cornelius et al 2010; Schaller et al 2009). We have described a hypotensive and bradycardic effect after a mouth opening, obtained by an ad hoc device, in both normotensive anesthetized rats and in normotensive humans (Lapi et al 2013, 2014, 2017; Del Seppia et al 2016, 2017). A lasting (up to 140 min) decrease of about 20 mmHg of mean blood pressure (MBP) was detected in the rat (Lapi et al 2013, 2014), while normotensive volunteers showed a prolonged systolic and diastolic pressure reduction of lesser extent (about 3–4 mmHg) when subjected to two different dilator devices, one allowing partial masticatory movements, defined dynamic extension (Brunelli et al 2012; Del Seppia et al 2016), and another with a fixed mouth opener, defined static extension (Del Seppia et al 2017), a similar study by other authors using dynamic extension failed to confirm these results (De Innocentiis et al 2015).
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