CARDIOPULMONARY CONTROL IN SLEEPING SPRAGUE-DAWLEY RATS TREATED WITH HYDRALAZINE

To test the hypothesis that hydralazine can suppress spontaneous sleep -related central apnea, respiratory pattern, blood pressure, and heart period were monitored in Sprague-Dawley rats. In random order and on separate days, rats were recorded after intraperitoneal injection of 1 ) saline or 2) 2 mg/kg hydralazine. Normalized minute ventilation (NVI ) declined significantly with transitions from wake to non-rapid-eye-m ovement (NREM) sleep (-5.1%; P = 0.01) and rapid-eye-movement (REM) sl eep (-4.2%; P = 0.022). Hydralazine stimulated respiration (NVI increa sed by 21%; P < 0.03) and eliminated the effect of state on N(V) over dot I. Blood pressure decreased by 17% after hydralazine, and the corr elation between fluctuations in mean blood pressure and N(V) over dot I changed from strongly positive during control recordings to weakly n egative after hydralazine (P < 0.0001 for each). Postsigh and spontane ous apneas were reduced during NREM and REM sleep after hydralazine (P < 0.05 for each). This suppression was strongly correlated with the r eduction in blood pressure and with the degree of respiratory stimulat ion. We conclude that mild hydralazine-induced hypotension leads to re spiratory stimulation and apnea suppression.