Baroreceptor reflex gain is not diminished in spontaneous hypertension

The magnitudes of both spontaneous and hypothalamically evoked sympathetic nerve activity are greater in spontaneously hypertensive rats (SHR) than in normotensive Wistar-Kyoto rats (WKY). Because the baroreceptor reflex influences the magnitude and time course of the sympathetic response to hypothalamic stimulation, we evaluated the role of the baroreceptor reflex in this sympathetic hyperresponsiveness. Changes in spontaneous nerve activity following comparable shifts in mean blood pressure (static reflex gain) were not different between the two strains. The effect of alterations in prestimulation blood pressure on the size of the evoked sympathetic response (response gain) was greater in SHR. Baroreceptor reflex inhibition resulting from the evoked blood pressure rise during hypothalamic stimulation (dynamic gain) was also greater in SHR. Expressing response magnitudes and gains as a percent of the spontaneous activity eliminated these strain differences. Interruption of the baroreceptor reflex resulted in equivalent percent increases in spontaneous and evoked activity in the two strains. Postdenervation levels of spontaneous and evoked nerve activity were greater in SHR. The results show that sympathetic hyperreactivity in SHR is not due to deficient baroreceptor reflex function.