The Up and Down regulations of receptors
In a situation where there is a chronic or continuous and increased exposure of a receptor to a ligand or drugs that acts as an antagonist (has inhibitory function), this results to an upregulation (increase) in the number of the receptors but when the receptor is exposed to an Agonist (promoter), it results to a downregulation or decrease in the receptor numbers on the cell membranes.
Take the insulin receptors for example, when they are exposed to Insulin for a very long time and continuously, it leads to a gradual decrease in their number by the process of receptor internalization and degradation which is caused by increased hormonal binding.
This means that over-reactivity of the islet of Langerhans that produces insulin can cause gradual damage to the Insulin receptor and this consequently results to type 2 insulin resistant diabetes mellitus.
The above does not actually apply in all cases because the nicotinic receptor acts otherwise. In cases of chronic exposure to agonists (nicotine), rather than donwregulation, there is an upregulation of the nicotinic receptors.
This explains why the intake of nicotine is addictive in nature. The more you are exposed to them, the more you wish to take them.
Why aged people are predisposed to type two diabetes
As we age, there is gradual decline and alterations in the receptor binding and post receptor response sensitivity.
The way your body receptor respond to drugs at young and adult stage diminishes as you grow older and it reaches a point where the receptors are no longer sensitive.
A typical example of this is seen in insulin resistant type 2 diabetes mellitus, where the insulin receptors are no longer sensitive to insulin because there has been a physiologic alterations in the receptor binding ability as well as their response sensitivity.
Though other factors like overweight or obesity, sedentary life style, high intake of calories etc can also make the insulin receptors insensitive to insulin.
The chemical interactions of drugs
The chemical interaction of a drug could either produces a very serious unwanted side effects. This usually occurs when some drugs are taken concurrently with other drugs.
Some could alter the effective absorption or metabolism of the primary drug while some may end up enhancing the therapeutic potency and efficacy of the primary drug. Some may not need to compete for receptors with the primary drug.
It is needful at this point to say that, not all drugs necessarily require receptor binding before they exert their therapeutic effects.
Some drugs are able to produce some effects without even altering or changing any cellular function of the biological system. Some are also able to exert effects without binding to receptors.
A typical example is the mechanism of action of most antacids (drugs used for the treatment of ulcers). These drugs are bases and they reduce the acidity of the stomach by simple reaction with the acid to produce a neutral salts.
In a nutshell, what we are trying to establish here is that, the action of drugs could be direct or indirect (binding to receptors or enzymes) and immediate or delayed (neuromuscular blocking agents or those that interfere with DNA synthesis).
In conclusion, pharmacodynamics helps us determine the dose response about drugs.
How they interact with the biological system of the body, their potency, max concentration and their interaction with others drugs and molecules.
Always remember, the Pharmacodynamics of a drug is dependent on its binding to biological targets or its interaction and concentration at the binding site.
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