BASAL AND STRESS-INDUCED RELEASE OF NORADRENALINE IN HYPOTHALAMUS OF SPONTANEOUSLY HYPERTENSIVE RATS AT DIFFERENT AGES

Basal and stress-induced noradrenaline (NA) release was studied by int racerebral microdialysis in the hypothalamic paraventricular nucleus o f spontaneously hypertensive rats (SHR) at different ages (9 weeks, 6, 18 and 24 months). NA was measured in 20-min dialysate samples by hig h performance liquid chromatography with electrochemical detection. Mi crodialysis sampling was done at baseline, during a 20-min immobilizat ion stress and for the next 100 min. Basal NA levels decreased with ag e, showing a highly significant correlation. Immobilization stress rai sed NA similarly in the four age groups (respectively 281%, 235%, 243% , 251% of baseline at 9 weeks, 6, 18, 24 months), indicating that the response to stress is maintained at all these ages and is not affected by the development of hypertension or by aging.