Intrinsic sympathomimetic activity is used particularly with beta blockers that can show both agonism and antagonism at a given beta receptor, depending on the concentration of the agent (beta blocker) and the concentration of the antagonized agent (usually an endogenous compound, such as norepinephrine).
This is a very interesting question Prof. Aldallal.
One of the side effects of beta blockers is bradycardia. Drugs with this particular property (ISA) perhaps cause less bradycardia since they are partial agonist (as well as antagonist) .They cause low level agonist activity at the beta adrenergic receptors while at the same time exerting receptor site antagonism (against endogenous catecholamines). These are used if a submaximal response is desired; i.e., less bradycardia, less reduction of cardiac output.
As far as intrinsic sympathomimetic activity of some beta blockers are concerned, they are of little benefit in the management of angina and tachyarrhythmias, compared to selective beta blockers (B1) which are full antagonists that block the endogenous effects of catecholamines.
Since they also act as beta stimulant, caution should be advised to use them rationally. The risk / benefit ratio is still unsettled and perhaps more clinical trials would shed more light on this topic.
These may be helpful.
http://www.sciencedirect.com/science/article/pii/S091450871200130X
http://www.ncbi.nlm.nih.gov/pubmed/1977302
http://www.ncbi.nlm.nih.gov/pubmed/6137381
Best Regards,
Sidharta
Also check these papers:
http://www.ncbi.nlm.nih.gov/pubmed/6139009
http://www.ncbi.nlm.nih.gov/pubmed/2883872
Another side effect of a beta blocker is that it counteracts the effects of your long-acting bronchodilator, a beta-agonist, which is a major asthma drug. It can render your inhalers less useful or useless. I hear that they are developing other kinds of blood pressure lowerers that will not have that serious side effect. I hope it's true.
Dear Ali, I found in RG a very informative paper (in attachment).
Beta blockers with ISA cause less RESTING Bradycardia but are capable of reducing exercise tachycardia in similar extent to those without ISA. In addition, there may be less peripheral vasospasm-cold feet. Because of ISA, such drugs are best avoided in angina and IHD
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