α-Methylnoradrenaline induced hypotension and bradycardia after administration into the area of the nucleus tractus solitarii
TL;DR: Bilateral injections of α-methylnoradrenaline into the area of the nucleus tractus solitarii of the brain stem caused a dose-dependent decrease of systemic arterial blood pressure and heart rate of anesthetized rats.
Abstract: Bilateral injections of α-methylnoradrenaline into the area of the nucleus tractus solitarii of the brain stem caused a dose-dependent decrease of systemic arterial blood pressure and heart rate of anesthetized rats. The effects were prevented and even reversed by a preceding injection of the α-adrenoceptor blocking agent phentolamine. Pressor doses of angiotensin II and of arginine-vasopressin at the same site failed to decrease blood pressure and heart rate.
Summary (1 min read)
- The central blood pressure lowering effect of a-methyldopa may be mediated by its metabolite a-methylnoradrenaline (Henning and Rubenson, 1971 ).
- Experiments in cats in which amethyldopa was infused into the vertebral artery indicate that the main site may be located in the medulla oblongata (Henning and Van Zwieten, 1968 ).
- Administration of noradrenaline into the medulla oblongata in the area of the nucleus tractus solitarii in the rat decreased blood pressure and heart rate (De Jong, 1974} .
- The present report describes the effect of local administration of a-methylnoradrenaline at the same medullary site on blood pressure and heart rate of anesthetized rats.
3. Results and discussion
- A-Methylnoradrenaline presumably is the metabolite which mediates the blood pressure lowering effect of a-methyldopa (Henning and Rubenson, 1971) .
- Central a-adrenoceptor blockade by intraventricularly administered phentolamine prevented the fall in blood pressure caused by a-methyldopa (Finch and Hauesler, 1973) .
- In the present study injection of phentolamine into the area of the nucleus tractus solitarii inhibited both the hypotension and bradycardia induced by ~-methylnoradrenaline.
- The present findings thus support the hypothesis that a-methyldopa acts through a-adrenoceptor stimulation in this particular region of the medulla oblongata (Van Zwieten, 1973) .
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Cites result from "α-Methylnoradrenaline induced hypot..."
...This contention is supported by the findings of others obtained in anesthetized animals that reflex bradycardia produced by elevation of arterial pressure is facilitated by the intracisternal administration of clonidine, an a-adrenergic agonist,(34)'(35) that norepinephrine injected directly into NTS acutely and transiently lowers blood pressure and HR (an effect, blocked by a-adrenergic antagonists),(7) and that the depressor effects of a-methylnorepinephrine is mediated, in part, through a-adrenergic receptors within the NTS itself.(36)...
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