Heart rate variability and baroreflex function in AT2 receptor-disrupted mice

We adapted telemetry and sequence analysis employed in humans to mice and measured heart rate variability and the spontaneous baroreflex sensitivity in angiotensin II type 2 (AT2) receptor-deleted (AT2 -/-) and wild-type (AT2 +/+) mice with either deoxycorticosterone acetate (DOCA)-salt hypertension or N(omega)-nitro-L-arginine methylester hydrochloride (L-NAME) hypertension. Mean arterial pressure leveled during the day at 101+/-1 mm Hg and during the night at 109+/-1 mm Hg in AT2 receptor-deleted mice, compared with 98+/-2 mm Hg (day) and 104+/-2 mm Hg (night) in wild-type mice. Mean arterial pressure increased in AT2 receptor-deleted mice with L-NAME to 114+/-1 mm Hg (day) and 121+/-1 mm Hg (night), compared with 105+/-2 mm Hg (day) and 111+/-2 mm Hg (night), respectively. DOCA-salt also increased day and night blood pressures in AT2 receptor-deleted mice to a greater degree than in wild-type mice. Heart rate variability in the time and frequency domain was not different between AT2 receptor-deleted mice and AT2 receptor-deleted mice at baseline. Systolic blood pressure variability in the low frequency band was lower in AT2 receptor-deleted mice (0.6+/-0.1 ms2 versus 3.9+/-1.3 ms2) than in wild-type mice. Baroreceptor-heart rate reflex sensitivity was significantly increased in AT2 receptor-deleted mice compared with wild-type mice (3.4+/-0.6 versus 2.1+/-0.5 ms/mm Hg). These differences remained after DOCA-salt and L-NAME treatments. We conclude that activation of the AT2 receptor impairs arterial baroreceptor reflex function, probably by a central action. These data support the existence of an inhibitory central effect of the AT2 receptor on baroreflex function.