Question

A person is admitted to hospital as he had a myocardial infarction. A cardiologist injected him ‘streptokinase’. Why?
A. It reduces hypertension.
B. It reduces the level of blood cholesterol.
C. It stimulates heartbeat.
D. It acts as a clot buster.

Answer 1

Myocardial infarction commonly known as a heart attack occurs as a result of decreased or no blood flow to the heart and causes damage to the heart muscle, due to which the normal pumping is affected and may be fatal. The main cause of myocardial infarction is the formation of thrombus.

Step by step answer: Option A) Hypertension can be one of the reasons which on prolongation can lead to coronary heart diseases. However, the streptokinase enzyme is not used to reduce hypertension. Mainly ACE inhibitors (Angiotensin Converting Enzyme inhibitors) are used to reduce hypertension.
Option B) Blood cholesterol is also another cause that can further, in the long run, lead to heart diseases. However, streptokinase does not function to reduce cholesterol. Statins are mainly used to reduce cholesterol as they inhibit HMG-CoA reductase, the regulatory enzyme needed to form cholesterol.
Option C) Cardiostimulatory drugs and not streptokinase are used to stimulate heartbeat. They act as beta-agonists to the receptors present in heart muscle and increase chronotropy i.e., heartbeat and dromotropy i.e. electrical conduction, and thus increases cardiac output.
Option D) Streptokinase is fibrinolytic which lyse the blood clots in the vessels. The three main domains of the enzyme streptokinase α, β, and γ bind to plasminogen and by hydrolysis and bond cleavage form plasmin from plasminogen. Plasmin is the activated factor that breaks down fibrin which is a major constituent of thrombin and thus dissolves clots.
Hence, the correct answer is option (D).

Note: Risk factors of myocardial infarction include diabetes, obesity, hypertension, low HDL cholesterol, and high LDL cholesterol, excessive alcohol consumption, smoking. These factors lead to the formation of atherosclerosis and thrombus in the blood vessels.