Functional antagonism

Definition

Functional antagonism: An antagonist may act at a completely separate receptor, initiating effects that are functionally the opposite of the agonist.

As we know, all of drug that had been taken by our body will produce some effects .Functional antagonism will diminish or even completely abolished this effect.

Example 1(Histamine and Adrenaline)

A classic example is the antagonism by epinephrine to histamine-induced bronchoconstriction. Histamine binds to H1 histamine receptors on bronchial smooth muscle, causing contraction and narrowing of the bronchial tree. Epinephrine is an agonist at Betta 2 adrenoceptors on bronchial smooth muscle, which causes the muscles to actively relax. This functional antagonism is also known as "physiologic antagonism." When this two agonist act independently of each other with opposing action,the effect of drug will be diminished.

HISTAMINE ADRENALINE

Vasodilation Vasoconstriction

Bronchoconstriction Bronchodilation

Example 2(Cortisol and Insulin)

Cortisol is released in response to stress, acting to restore homeostasis. Unfortunately, cortisol counteracts with insulin, contributes to hyperglycemia-causing hepatic gluconeogenesis and inhibits the peripheral utilization of glucose (insulin resistance) by decreasing the translocation of glucose transporters (especially GLUT4) to the cell membrane .So it will inhibit the utilization of glucose and activate the gluconeogenesis.

While insulin is secreted in a response of the beta cells to a stimulus which will convert glycogen to glucose.This will increase utilization of glucose for our body.

These two hormones have an opposite actions. So when this two antagonists act independently of each other with opposing actions, it will diminished the effects.

Cortisone Insulin

Inhibit utilization of glucose Activate utilization of glucose