Renal sympathetic nerve activity after dexmedetomidine in nerve-intact and baroreceptor-denervated rabbits

To determine the effects of intravenous dexmedetomidine (DMED) on the sympathetic nervous system and to elucidate the mechanism of hypotension, we administered 3 micrograms/kg of DMED to nerve-intact and baroreceptor-denervated rabbits and compared the changes in renal sympathetic nerve activity (RSNA) and hemodynamic variables. In nerve-intact animals, mean arterial pressure (MAP) was increased briefly and then decreased significantly. Changes in RSNA were reciprocal to those of MAP. Heart rate decreased throughout the period of observation. In baroreceptor-denervated rabbits, both MAP and RSNA decreased significantly (-39.4% +/- 3.8% and -21.3% +/- 4.7%, respectively) after the initial increase of MAP. Twenty minutes after administration, hypotension had still continued (-21.1% +/- 3.2%) although RSNA returned to the baseline value. These results indicate that suppression of sympathetic nerve discharge is indeed one of the mechanisms of DMED-induced hypotension, although it may not be the principal one.