Wirkung von Angiotensin auf Funktion und Noradrenalinabgabe isolierter Kaninchenherzen in Ruhe und bei Sympathicusreizung
SchlüsselwörterAngiotensin Noradrenalinabgabe Isoliertes Kaninchenherz Sympathische Nerven
The influence of angiotensin on the isolated rabbit heart perfused at constant pressure or constant flow was investigated at rest and during electrical stimulation of the postganglionic sympathetic nerves.
In low concentrations (32–100 ng/min or 1.4–5.3 ng/ml) angiotensin had considerable positive inotropic effects, while its chronotropic effects were weak and variable. High concentrations decreased the rate of beat, and an increase in the height of contraction was preceded by a transient phase of inhibition. In hearts perfused at constant pressure, angiotensin diminished coronary flow. The positive inotropic effect of angiotensin was not accompanied by the appearance of increased amounts of noradrenaline in the venous effluent.
Angiotensin caused a dose-dependent increase in the output of noradrenaline induced by sympathetic nerve stimulation. The peptide was most potent in hearts perfused at constant flow; the threshhold dose of angiotensin for this procedure was 3.2 ng/min (128 pg/ml), and maximal effects (i.e., an increase by 81%) were observed with 32 ng/min (1.28 ng/ml). Doses about three times higher were required to obtain similar effects in hearts perfused at constant pressure. The reduction of coronary flow as seen under these conditions may be responsible for the weaker effect of angiotensin. Continuous infusion increased the output of noradrenaline during several successive stimulation periods.
In most cases, the increase in output of noradrenaline induced by angiotensin did not lead to an increase in the response of the pacemaker or of the myocardium to sympathetic stimulation. Only in hearts perfused at constant flow during infusion of 32 ng/min of angiotensin the positive inotropic effect of sympathetic stimulation was significantly augmented.
The results indicate that angiotensin may modulate the activity of the autonomic nervous system by influencing peripheral sympathetic nerves.
Key-WordsAngiotensin Noradrenaline Release Isolated Rabbit Heart Sympathetic Nerves
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