Spontaneously hypertensive rats: Adrenergic hyperresponsivity to anticipation of electric shock

Spontaneously hypertensive (SHR) and normotensive (WKY) male rats were transferred daily for 4 consecutive days from their home cages to a shock chamber and, after 5 min, received 60 footshocks (2.5 mA, 0.4 sec in duration, every 5 sec). Control animals of each strain were handled in the same manner but were never shocked. Blood samples were obtained from each rat on the fifth day via a chronic, indwelling tail arterial catheter. Previous exposure to footshock had no effect on plasma levels of norepinephrine (NE) and epinephrine (EPI) while animals were undisturbed in their home cages. After transfer to the shock chamber, the increases in plasma levels of NE and EPI were greater in previously shocked SHR than in unshocked SHR or shocked WKY rats. In addition, the increase in heart rate associated with transfer to the shock chamber was greater in previously shocked SHR rats than in unshocked SHR or in WKY controls. Previously shocked animals of both strains were also less active and defecated more frequently than controls when placed into the shock chamber. These results indicate that SHR and WKY rats have similar behavior responses to anticipation of footshock, but only in SHR rats is this attended by enhanced adrenergic responsivity.