Evidence in hypertensive rats of hypotensive effect after mandibular extension

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.