Sympathetic-adrenal medullary response to stress in hyperactive and hypertensive rats

Sympathetic-adrenal medullary hyperreactivity to acute stress, measured as an exaggerated elevation of plasma epinephrine and norepinephrine levels in response to footshock, was examined in four genetically related, inbred rat strains, all derived from the Wistar-Kyoto rat (WKY). These four strains are endowed with the traits of hypertension and behavioral hyperactivity, expressed either together (in SHR), or separately in two new strains (Wistar-Kyoto hyperactive rats, WK-HA, and Wistar-Kyoto hypertensive rats, WK-HT), or not at all (in WKY). Male rats of the SHR, WKY, WK-HA and WK-HT strains were subjected to acute footshock stress in order to determine whether the previously reported hyperreactivity of the SHR is attributable to the hypertensive trait, or to the behavioral hyperactivity trait, both of which are characteristic of the SHR. Plasma catecholamine levels were determined prior to, immediately following, and 5 min following acute footshock stress. We report here that the WK-HA strain (hyperactive but not hypertensive) exhibited the hyperreactivity characteristic of SHRs, and not the WK-HT strain (hypertensive but not hyperactive). We conclude that the exaggerated sympathetic-adrenal medullary response to acute stress is associated with the hyperactivity trait and not with hypertension among these congenic rat strains.