Download Haron kirikiru Effects of inotropics on contractility of the heart

Haron kirikiru
Effects of inotropics on contractility of the heart
Inotropic agents are substances that change the force of muscular contraction, either positively or negatively. Factors that increase
contractility are termed as positive inotropic agents. They typically stimulate Calcium ions entry into cardiac muscle cells increasing the force
and duration of ventricular contractions. Negative inotropics may block Calcium ions movement or depress cardiac muscle metabolism thereby
reducing heart contractility.
Epinephrine has a positive inotropic effect; it is released by suprarenal medullae. Norepinephrine is released by postganglionic fibers
of the cardiac nerves and by the suprarenal medullae. SNS stimulate cardiac muscles cells metabolism and increase the force and degree of
contraction by stimulating alpha and beta receptors in cardiac muscle plasma membrane, thereby increasing ventricular contraction.
Isoproterenol, dopamine, and dobutamine mimic the action of Epinephrine and Norepinephrine by stimulating beta 1 receptors on cardiac
muscles. Dopamine stimulates calcium ions entry through alpha one receptors stimulation. Digitalis interferes with the removal of calcium ions
from sarcoplasm of cardiac muscles leading to an elevated calcium ions concentration and eventually a stronger heart muscle contraction.
PNS has negative inotropic effect on cardiac muscle contractility, ACh produces hyperpolarization and inhibition at the membrane
surface of cardiac muscle cells, which results to a reduced ventricular contractions. Beta and alpha blockers such as labetalol mimic the actions of
ACh. They are mainly used to treat hypertension by preventing or reducing sympathetic stimulation of the heart. Calcium channel blockers such
as nifedipine reduce the level of calcium ions in the cells, thereby reducing contractility.
Sources:
Fundamentals of human anatomy & physiology, 8 th edition
Pharmacology and the nursing process, 6th edition