Changes in hemodynamic characteristics in response to shaking stress with advancing age in spontaneously hypertensive rats.

Changes in hemodynamic parameters following "shaking" in 4, 12, 24 and 48 week old spontaneously hypertensive rats (SHR) and Wistar rats of the Kyoto strain (WKY) were analyzed. Mean arterial pressure (MAP) and cardiac output (CO) were measured in the following two conditions: (A) at rest, and (B) after shaking (these parameters were measured following a 3-sec rest after 5-sec of shaking). Both sets of data were compared in each age group between SHR and WKY. Heart rates (HR) in all age groups of SHR and WKY were significantly increased after shaking compared with those at rest. MAP in 4 week old SHR, but not in 4 week old WKY, was increased compared with that at rest. In 48 week old SHR and WKY, MAP after shaking was not increased compared with that at rest. This increased MAP induced by stress (shaking) in young SHR may be related to a causative factor in hypertension. CO in SHR did not indicate changes in shaking reaction as a result of increasing aging. Heart work index (HWI) after shaking in all age groups of SHR, including the prehypertensive stage, was significantly increased compared with that at rest; this was not the case in WKY. The intermittently increased heart work seen in response to stress may contribute to the early development of left ventricular hypertrophy in young SHR.