α2b‐Adrenergic receptors modulate baroreflex sensitivity

Deoxycorticosterone acetate (DOCA)‐salt hypertension is associated with enhanced sympathetic activity and impaired baroreflex sensitivity (BRS). Blockade of central α2‐adrenoceptors (α2‐AR) attenuates DOCA‐salt hypertension onset and severity and inhibits BRS. Renal α2B‐AR are increased in DOCA‐salt hypertension and regulate sodium retention. We hypothesized mice with decreased α2B‐AR expression would have impaired BRS, attenuated DOCA‐salt hypertension and be more sensitive to uninephrectomy (nx). Blood pressure (BP) and heart rate (HR) were measured using radio‐telemetry in intact and nx heterozygous α2B‐AR null mice (HET) and wild‐type (WT) littermates for 3 control and 14 DOCA‐salt (50 mg DOCA pellet, 1% NaCl, 1% KCl water) treated days. DOCA‐salt increased BP similarly in both intact groups (p<0.05). BP was higher in HET‐nx than HET‐intact mice on all days (p<0.05) but nx did not affect BP in WT groups. HR decreased in a BP‐dependent manner in WT mice but did not change in HET mice. BRS in response to acute changes in BP were evaluated in isoflurane anesthetized HET and WT mice given phenylephrine (IP) to increase BP. HR decreased with increases in BP in WT mice but increased in HET mice. Therefore BRS is impaired in HET mice and α2b‐AR appear to be required for sympathetic withdrawal in response to both acute and chronic increases in BP.