Norepinephrine reuptake, baroreflex dynamics, and arterial pressure variability in rats

This study examined the effect of norepinephrine reuptake blockade with des ipramine (DMI) on the spontaneous variability of the simultaneously recorde d arterial pressure (AP) and renal sympathetic nerve activity (SNA) in cons cious rats. Acute DMI administration (2 mg/kg iv) depressed AP Mayer waves (similar to 0.4 Hz) and increased low-frequency (<0.2 Hz) components of AP variability. DMI decreased renal SNA variability, especially due to the abo lition of oscillations related to Mayer waves. To examine whether DMI-induc ed changes in AP and renal SNA variabilities could be explained by alterati ons in the dynamic characteristics of the baroreceptor reflex loop, the fre quency responses of mean AP to aortic depressor nerve stimulation were stud ied in urethan-anesthetized rats. DMI accentuated the low-pass filter prope rties of the transfer function without significantly altering the fixed tim e delay. The frequency responses of iliac vascular conductance to stimulati on of the lumbar sympathetic chain were studied in an additional group of a nesthetized rats. DMI did not markedly alter the low-pass filter properties of the transfer function and slightly increased the fixed time delay. Thes e results suggest that the DMI-induced decrease in the dynamic gain of the baroreceptor reflex is responsible for the decreased spontaneous renal SNA variability and the accompanying increased AP variability. The "slowing dow n" of baroreflex responses cannot be attributed to an effect of DMI at the vascular neuroeffector junction.