| Abstract: | Circulating levels of norepinephrine (NE), epinephrine (EPI), dopamine-β-hydroxylase (DBH), and corticosterone were compared in spontaneously hypertensive (SHR) and Wistar-Kyoto normotensive (WKY) rats during recovery from a 2-hr period of immobilization stress. On the day before the experiments, a catheter was inserted into the ventral caudal artery of each rat to measure directly blood pressure and heart rate and to obtain samples of blood from conscious, unhandled rats. Immediately prior to the period of forced immobilization, while animals were at rest in their home cages, plasma levels of NE and EPI did not differ between rats of the 2 strains. After 2 hr of immobilization, circulating levels of NE, EPI, and DBH were significantly higher in SHR rats than in WKY rats. In contrast, increments in mean blood pressure after 2 hr of stress were greater in WKY rats. When compared to WKY rats, SHR rats had significantly higher circulating levels of NE, EPI, and DBH for up to 4 hr after the period of immobilization. These results are consistent with the view that the sympatho-adrenal medullary system of SHR rats is more responsive than WKY rats to immobilization stress. In addition, in SHR rats, the sympatho-adrenal system remains in a heightened state of activity for a longer period of time following stressful stimulation. The excessive and prolonged discharge of catecholamines into the circulation during stress may be an important factor in the etiology of this form of experimental hypertension. |
