Sympatho-adrenal responses of spontaneously hypertensive rats to immobilization stress.

Blood pressure, heart rate, and circulating levels of norepinephrine, epinephrine, and corticosterone were measured before and during the first or seventh period of immobilization stress (150 min per day) in spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) normotensive male rats. A catheter was inserted into the tail artery of each rat to permit direct measurement of blood pressure and heart rate and serial sampling of blood in conscious, unhandled animals. During the first immobilization, SHR rats had significantly higher circulating levels of norepinephrine, epinephrine, and corticosterone than did WKY rats. One day after the sixth immobilization, basal levels of norepinephrine and epinephrine were significantly higher and mean blood pressure was significantly lower in repeatedly stressed SHRs compared to unstressed SHRs. In addition, adaptation to the repeated stress in SHRs was attended by reduced adrenomedullary secretion and an increased blood pressure response. These results demonstrate that adaptive changes in the cardiovascular and sympatho-adrenal medullary systems of repeatedly immobilized rats are greater in SHR than in WKY rats.