One of two chemical compounds that cells use to make the building blocks of DNA and RNA. Examples of purines are adenine and guanine. Purines are also found in meat and meat products. They are broken down by the body to form uric acid, which is passed in the urine. High levels of uric acid in the body may cause gout.

1. m.v.vijayendra
MS pharm

2. introduction
 Nucleosides especially adenosine and nucleotides such as ATP and
ADP these molecule are play vital role in DNA/RNA synthesis and
energy metabolism.

3. Purinergic receptors
 Depending upon conversion of ADP,AMP and adenosine.
 Adenosine receptors (A1, A2A, A2B and A3), formerly known as P1
receptors before the agonist was discovered to be adenosine. These
are G protein– coupled receptors that act through adenylyl cyclase/
cAMP, or by direct effects on Ca2+ and K+ channels.
 P2Y metabotropic receptors (P2Y1–14), which are G protein–coupled
receptors that utilize either phospholipase C activation or cAMP as
their signaling system
 P2X ionotropic receptors (P2X1–7) which are trimeric (in many cases
heterotrimeric) ATP-gated cation channels. e presence of ATP, the
channels become permeable to Ca2+ and Na+ ions, activating Ca2
sensitivity cause membrane depolarization

5. ADENOSINE AND THE CARDIOVASCULAR SYSTEM
Adenosine inhibits cardiac pacemaker activity and atrioventricular node
conduction and it is likely that all four of the adenosine receptors are
involved in these effect.
β-adrenoceptor antagonists or verapamil. Regadenoson, a powerful
vasodilator used for diagnostic tests of cardiac function.

6. adenosine in asthma
 activation of the A2A subtype exerts a largely protective and anti-inflammatory effect,
but acting through its A1 receptor, adenosine promotes mediator release from mast
cells, and causes enhanced mucus secretion, bronchoconstriction and leukocyte
activation.
 Methylxanthines, especially analogues of theophylline are adenosine receptor
antagonists.
 Theophylline has been used for the treatment of asthma and part of its beneficial
activity may be ascribed to its antagonism of the A1 receptor. however,
methylxanthines also increase cAMP by inhibiting phosphodiesterase, which
underwrites some of their pharmacological actions independently of adenosine
receptor antagonism.
 Certain derivatives of theophylline are claimed to show greater selectivity for
adenosine receptors over phosphodiesterase.

7. adenosine in inflammation
Adenosine also regulates the inflammatory response elsewhere and A
receptors at various locations in the eye (particularly A2A receptors)
have been identified as potential targets in ocular diseases.
Ant inflammatory is hydrolysis of ATP and AMP by producing
ectonucleotides .

8. Adenosine in CNS
A1 and A2A receptors, adenosine has an inhibitory effect on many CNS
neurons, and the stimulation experienced after consumption of
methylxanthines such as caffeine and theophylline.
Antagonism of adenosine receptors by the methylxanthines