Page 160 - phytochemistry I - PharmD Clinical

3. The presence of β-OH group at position C-3, which is involved in
the glycosidic linkage.

4. The presence of β-OH group at position C-14.
5. A/B ring junction cis, B/C ring junction trans and C/D ring junction

cis.
6. Additional OH group at C-5, C-11 and C-16 may be present.

Effect of cardiac glycosides on the heart muscle:

• Cardiac failure occurs when the heart is unable to pump blood
effectively at a rate that meets the needs of the body. The heart
muscle can perform only weakly, particularly on ventricular
contraction. This reduced pumping capacity results in a reduced
heart output. However, as new blood continues to enter the heart,
the volume of blood in the heart increases. As the heart is unable
to pump this blood out, it becomes congested, hence ‘congestive
heart failure’.

• Cardiac glycosides exert a positive inotropic effect on the heart in
cardiac failure.

• Cardiotonic agents are used for treatment of congestive heart
failure and cardiac arrhythmias. They are characterized by highly
specific action on the cardiac muscle, increase the force of systolic
contraction and shorten the length of the systole. Thus allowing the
weakened heart to function more efficiently.

Mechanism of action on the heart muscle:

• Cardiac glycosides inhibits the cellular sodium-potassium ATPase
pump that pumps sodium out of and transports potassium into
contracting and conducting cells.

• By reducing the exchange of extracellular sodium with intracellular
calcium, digoxinraises the store of intracellular calcium, which
facilitates muscular contraction.

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