Cardiac glycosides are similar in their chemicalstructure with bile acids, cortisone, vitamins, hormones, cholesterol. These substances are natural metabolites that support the normal functioning of the heart.
Cardiac glycosides consist of glycine (sugar) andaglycone. It is the aglucone that acts as the determining factor in the pharmacological activity of the drug. Entering into the reaction with other active substances provides an unsaturated five-membered ring in their structure.
Cardiac glycosides for tissues and organsdistributed unevenly. The target of their action is the myocardium, which accumulates only 10% of the drug, another 50% is fixed in the striated muscle, where they do not cause any effect.
By duration of action, cardiac glycosides are divided into:
- long - digitoxin,
- medium - digoxin,
- short - strophantine, korglikon.
Cardiac glycosides: mechanism of action
In a normal state, the cardiomyocyte contains30 times more potassium and 20 times less sodium. At rest, the outer surface of the cell membrane is positively charged, while the inner surface is negatively positively charged. When excitation is caused by the depolarization of membranes: sodium and calcium enter the cell. During this process, potassium can not pass through the cell membrane. As soon as they leave the cell, the process of repolarization begins. This moment occurs immediately before the contraction of the muscle. Thus, the amount of calcium that enters enters the cell reduction. The potassium ions remaining in the cell are antagonists of this process.
Cardiac glycosides accelerate the onsetrepolarization and provide the maximum yield of potassium from cardiomyocytes. After reduction, it is necessary to restore the balance of ions inside and outside the cell (potassium return and sodium yield). This process depends on the energy reserve of the cell, is provided by the enzyme ATPase. Its active center is the sulfhydryl group. Cardiac glycosides block the active site, reducing activity. All this leads to the fact that sodium ions remain in the cell, and this accelerates the onset of the next depolarization. If the content of potassium ions decreases significantly, the synthesis of creatinine phosphate is violated, which causes a reduction in the strength of the contraction of the heart muscle.
Cardiac glycosides: contraindications
Absolute contraindicationsto their application are: atrioventricular blockade of the II degree, sinus bradycardia, allergic reactions to these drugs, intoxication by them.
To relative contraindicationsinclude the following: fibrillation bradyarrhythmia, AV-blockade of the 1st degree, sinus node weakness syndrome, IHD, sinus bradycardia, hypertensive heart, hypercalcemia, hypokalemia, renal or pulmonary insufficiency in the anamnesis.
It is inappropriate to usecardiac glycosides under the following conditions: amyloidosis of the heart, diastolic heart overload in volume with aortic insufficiency, thyrotoxicosis, acute myocardial infarction, cardiomyopathy, constrictive pericarditis, heart failure with high cardiac output, anemia and so on.
Immediately the contraindications themselves are due toabsence of systolic dysfunction, which explains the inefficiency of using cardiac glycosides. And, for example, with the development of acute myocardial infarction, their use can provoke the development of arrhythmias, which gives an unfavorable prognosis for the further life of the patient.
Before using cardiac glycosides, always consult with a specialist. This will help prevent the development of serious complications.