Abstract
The characteristics of voltage-dependent45Calcium uptake and norepinephrine release as factors controlling neural activities in the hypothalamus which is an important regulatory site for cardiovascular function were studied. Two groups of animals: male spontaneously hypertensive rat (SHR) and age-matched normotensive wistar rat (NW) were used in this study. Animals at 4, 6 and 16 weeks of age were sacrificed by decapitation and the hypothalamus was dissected out. Voltage-dependent calcium uptake and norepinephrine release were determined from hypothalamic synaptosomes either in low potassium (5 mM) or high potassium (41 mM) stimulatory conditions by using45Ca isotope and HPLC-ECD techniques. Degrees of voltage-dependent45calcium uptake and norepinephrine release evoked by calcium uptake in the hypothalamus of prehypertensive phase (4 weeks old) of SHR were significantly smaller than those in NW of the same age. However, in the developmental phase (6 weeks old) and the established phase (16 weeks old) of hypertension in SHR, degrees of voltage-dependent45calcium uptake and norepinephrine release were similar to those of age-matched normotensive wistar rats. These data imply that the deficit in hypothalamic norepinephrine release might be an important underlying factor for the development of hypertension in SHR.
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