DECREASED NOREPINEPHRINE CONTENT IN THE MEDULLA-OBLONGATA IN SEVERELYHYPERTENSIVE RATS

1. To clarify possible abnormalities in catecholamines in the medulla oblongata in relation to severe hypertension, the authors measured cha nges in catecholamine levels in the medulla oblongata of malignant str oke-prone spontaneously hypertensive rats (M-SHRSP). Effects of the ad renal medullae and peripheral nerves were ruled out by adrenal demedul lation and chemical sympathectomy. 2. The level of norepinephrine in t he medulla oblongata was significantly lower in untreated M-SHRSP than in untreated WKY (control) rats at 10 weeks of age. Further, it was s ignificantly lower in treated M-SHRSP than in the treated WKY group at both 6 and 10 weeks of age. The level of epinephrine in 6 week old tr eated M-SHRSP was significantly higher than that in age-matched treate d WKY, but no other differences were observed in terms of epinephrine content. There were no age- or treatment-related differences in dopami ne levels in the medulla oblongata. 3. Since norepinephrine has an inh ibitory effect on blood pressure elevation in the nucleus tractus soli tarii (NTS) in the medulla oblongata, the suppression of negative feed back due to a decrease in the activity of inhibitory neurons in the me dulla oblongata appears to be involved in the development and progress ion of severe hypertension in M-SHRSP.