Mechanism of Action

Labetalol produces equilibrium-competitive antagonism at p-receptors but does not exhibit selectivity for p1- or p2-receptors. Like certain other p-blockers (e.g., pindolol and timolol), labetalol possesses some degree of intrinsic activity. This intrinsic activity, or partial ago-nism, especially at p2-receptors in the vasculature, has been suggested to contribute to the vasodilator effect of the drug. The membrane-stabilizing effect, or local anesthetic action, of propranolol and several other p-blockers, is also possessed by labetalol, and in fact the drug is a reasonably potent local anesthetic.

The a-blockade produced by labetalol is also of the equilibrium-competitive type. In a manner similar to prazosin, labetalol exhibits selectivity for a1-receptors. Presynaptic a-receptors, which are of the a2 subclass, are not antagonized by labetalol. The drug also has some intrinsic activity at a-receptors, although this action is less than its intrinsic p-receptor-stimulating effects.

Labetalol appears to produce relaxation of vascular smooth muscle not only by a-blockade but also by a partial agonist effect at p2-receptors. In addition, la-betalol may produce vascular relaxation by a direct non-receptor-mediated effect.

Labetalol can block the neuronal uptake of norepi-nephrine and other catecholamines. This action, plus its slight intrinsic activity at a-receptors, may account for the seemingly paradoxical, although infrequent, increase in blood pressure seen on its initial administration.

10 Ways To Fight Off Cancer

10 Ways To Fight Off Cancer

Learning About 10 Ways Fight Off Cancer Can Have Amazing Benefits For Your Life The Best Tips On How To Keep This Killer At Bay Discovering that you or a loved one has cancer can be utterly terrifying. All the same, once you comprehend the causes of cancer and learn how to reverse those causes, you or your loved one may have more than a fighting chance of beating out cancer.

Get My Free Ebook

Post a comment