NORADRENALINE: PHARMACOLOGICAL HIGHLIGHTS & COMPARISON WITH ADRENALINE 

Noradrenaline (Norepinephrine) is a directly and indirectly acting sympathomimetic amine which stimulates alpha 1 and β1 adrenoceptors, but, in contrast to Adrenaline (epinephrine), has little effect on β2 adrenoceptors.

🖍These actions produce positive inotropic effects, intense vasoconstriction, increases in arterial pressure, and relative maintenance of cardiac output.

🖍Noradrenaline increases arterial pressure while simultaneously enhancing contractile state and venous return by reductions in venous capacitance, thereby augmenting stroke volume and ejection fraction. In contrast, pure alpha 1 adrenoceptor agonists such as phenylephrine and methoxamine further compromise cardiac output in failing myocardium and contribute to peripheral hypoperfusion despite an increase in arterial pressure.

🖍In contrast to adrenaline, noradrenaline does not substantially affect heart rate because activation of baroreceptor reflexes resulting from arterial vasoconstriction usually counteracts β1 mediated, direct, positive, chronotropic effects.

🖍Its arrhythmogenic potential is considerably less than that of adrenaline. Thus, substitution of noradrenaline for adrenaline may be appropriate in the therapeutic management of cardiogenic shock when atrial or ventricular arrhythmias are present.

🖍Intravenous infusions of noradrenaline (0.03–0.90 mg kg –1 per minute) have been shown to increase arterial pressure, LV stroke work index, cardiac index, and urine output in septic patients with hypotension that was unresponsive to volume administration, dopamine, or dobutamine

🖍Causes relatively greater increases in systemic vascular resistance and diastolic arterial pressure than adrenaline.

🖍The drug has a duration of action of 30–40 minutes; tachyphylaxis occurs with prolonged administration.

🖍The drug produces coronary vasodilatation, leading to a marked increase in coronary blood flow. However, as myocardial work may increase, the balance of myocardial oxygen consumption and delivery may lead to ischaemia on noradrenaline.

🖍Reflex vagal stimulation leads to a compensatory bradycardia

 🖍The cerebral blood flow and oxygen consumption are decreased by the administration of noradrenaline; mydriasis also occurs

🖍The glomerular filtration rate is usually well maintained with noradrenaline; but it decreases the renal blood flow and this represents a major limitation on the prolonged use of high doses of norepinephrine.

🖍Noradrenaline increases the contractility of the pregnant uterus; this may lead to fetal bradycardia and asphyxia

🖍Noradrenaline may decrease insulin secretion, leading to hyperglycaemia

🖍The drug is pharmaceutically incompatible with barbiturates and sodium bicarbonate

(Reference: Paul S. Pagel and David C. Warltier, Essential drugs in anesthesia practice Positive inotropic drugs, Anesthetic Pharmacology, 2nd edition)

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