The therapeutic effects of cardiac glycosides

Cardiotonic drugs from the cardiac glycoside group (digitaloids) largely increase the strength of congestive cardiac muscle contractions as well as the sensitivity of their tissue and their muscular tension. At the same time they inhibit the frequency of contractions as well as the conductivity of impulses in the stimulatory conductive cardiac system. The positive inotropic effect of glycosides has been demonstrated to be based on the inhibition of the action of a specific receptor associated with the inhibitory role of the potassic-sodium pump. The inhibition of the Na+-K+-ATP-ase function (adenosine triphosphatase) increases the concentration of Na+ ions inside the cells, which in turn stimulate an increase of Ca2+ ion transfer into cells belonging to the cardiac muscle from the extracellular environment, basjng on the exchange of Na+ ions for Ca2+ ions. An increased concentration of Ca2+ ions intensifies the transfer of free Ca2+ ions from the sarcoplasmatic reticulum storage vesicles. Moreover, it increases the contractability of cardiac muscle fibres. As a result of this activity the contraction intensity and its amplitude are increased. The cardiac output and the blood flow volume of the heart per minute are also increased, as well as the influx of noncirculating blood, renal blood flow and renal diuresis. The circulatory edema has been reduced.