Impaired heart function and noradrenaline release after ischaemia in stroke-prone spontaneously hypertensive rats

1. Stroke-prone spontaneously hypertensive rats (SHRSP) are a strain of rat that exhibit severely high blood pressure and stroke attacks at an early age, but their heart function in vitro has seldom been studied in detail. Although the activity of the sympathetic nervous system is known to increase after myocardial ischaemia, there is little information about the cardiac release of noradrenaline (NA) associated with heart function after ischaemia in SHRSP. The aim of the present study was to examine heart function and cardiac NA release after ischaemia in SHRSP. 2. Isolated hearts of 4- and 8-month-old SHRSP and age-matched Wistar-Kyoto (WKY) rats were perfused in a working heart preparation and were subjected to 30 min ischaemia followed by 30 min reperfusion. Heart function and coronary flow were monitored throughout the experiment. Coronary effluent was collected for determination of NA using high-performance liquid chromatography coupled with electrochemical detection. 3. Under baseline conditions, cardiac output of 4-month-old SHRSP was slightly but significantly decreased compared with that of WKY rats (P < 0.05), although coronary flow was maintained normally at this age. Eight-month-old SHRSP showed a further impairment of systolic heart function, with lower coronary flow and higher coronary vascular resistance under baseline conditions. Elevated left ventricular end-diastolic pressure was evident in SHRSP at both ages before ischaemia. Heart function was severely damaged after 30 min global ischaemia in SHRSP from both age groups. Stroke-prone spontaneously hypertensive rats also showed lower coronary flow and higher coronary vascular resistance during reperfusion. 4. Coronary NA was not detectable in WKY rats or SHRSP at 4 months of age under baseline conditions. In 8-month-old SHRSP, pre-ischaemic NA release was significantly higher than that in age-matched WKY rat controls. The concentration of NA in the coronary effluent of SHRSP during reperfusion was also significantly higher than that of WKY rats at both ages. 5. These data demonstrate that SHRSP have early impairment of both systolic and diastolic heart function compared with WKY rats. Severe damage of heart function and coronary flow after ischaemia in SHRSP was accompanied with an increased release of NA, which may play a harmful role in heart function impairment in SHRSP after ischaemia.