Effect Of Various Drugs On Dog Blood Pressure And Heart Rate l MBBS Experimental Pharmacology

Summary

This video tutorial covers the demonstration of drug effects on blood pressure, focusing on various drugs used in MBBS practical exams. It explains the biophysical responses, mechanisms of action, and how to identify unknown drugs through their unique graph patterns. Key drugs such as epinephrine, acetylcholine, histamine, and propranolol are discussed in detail, alongside concepts like vasomotor reversal and receptor activity. The tutorial aims to provide students with a clear understanding of how to interpret drug-induced changes in blood pressure and heart rate, with tips on identifying drugs in exam conditions.

Takeaways

• 😀 Understanding the autonomic nervous system is essential for performing the blood pressure experiment in the Kya software.
• 😀 The Kya software includes 11 drugs, starting with epinephrine (adrenalin), which causes a bi-physical response that affects both BP and heart rate.
• 😀 Epinephrine initially causes BP to rise through alpha receptor stimulation, but later decreases BP as beta receptors are stimulated at lower concentrations.
• 😀 Non-selective alpha blockers like fentolamine prevent the vasodilation effect of adrenaline, leading to only an increase in BP when adrenaline is re-administered.
• 😀 The decrease in BP observed with beta blockers like propranolol results from a reduction in cardiac output, despite beta receptor inhibition.
• 😀 Acetylcholine has dual effects on the heart, stimulating M2 receptors to decrease heart rate and M3 receptors to cause vasodilation and lower BP.
• 😀 Reflex actions play a role in the changes to heart rate, especially when BP increases, as observed with drugs like acetylcholine and histamine.
• 😀 Histamine stimulates H1 and H2 receptors, leading to vasodilation and a decrease in BP, along with a reflex increase in heart rate.
• 😀 Indirectly acting drugs like ifterin increase both BP and heart rate, but with repeated doses, the graph shows a decrease in effect, known as colaxis.
• 😀 In experiments with unknown samples, the antagonist drug can be used to help identify the agonist, helping differentiate between drugs with similar effects on BP and heart rate.

Q & A

What is the purpose of the 'Kya Experiment' in the MBBS curriculum?

The 'Kya Experiment' demonstrates the effect of various drugs on blood pressure using a computer-assisted learning software. It is an important part of the MBBS practical exam, with a focus on understanding how different drugs impact blood pressure and heart rate.

Why is it important to understand the autonomic nervous system before conducting the experiment?

Understanding the autonomic nervous system (ANS) is essential because the drugs studied in the experiment affect both the heart and blood vessels through their actions on the ANS. Knowing the distribution and functions of alpha and beta receptors in the body helps interpret the experimental results.

What is the significance of the graph observed after administering epinephrine (adrenaline)?

The graph shows a biphasic response. Initially, blood pressure rises due to the stimulation of alpha receptors, causing vasoconstriction. As the concentration of adrenaline decreases, beta receptors are stimulated, causing vasodilation and a subsequent drop in blood pressure.

How does the non-selective alpha blocker (fentolamine) affect the response to adrenaline?

When fentolamine, a non-selective alpha blocker, is administered before adrenaline, it blocks the alpha receptors, preventing vasoconstriction. As a result, adrenaline primarily affects beta receptors, causing a rise in blood pressure instead of a decrease, leading to a phenomenon known as vasomotor reversal.

What causes the decrease in heart rate when adrenaline is administered?

The decrease in heart rate is caused by the reflex action triggered by the increase in blood pressure. Stretch receptors in the aortic sinus detect the rise in pressure and send signals to reduce the heart rate as part of a feedback mechanism.

Why does acetylcholine reduce heart rate despite increasing blood pressure?

Acetylcholine stimulates M2 receptors in the heart, reducing the heart rate. Simultaneously, it stimulates M3 receptors in blood vessels, causing vasodilation and a fall in blood pressure. The heart rate is decreased due to the M2 receptor's action, despite the blood pressure increase caused by vasodilation.

What is the role of histamine in the experiment, and how does it affect blood pressure and heart rate?

Histamine is an inflammatory mediator that causes vasodilation by stimulating H1 and H2 receptors. This leads to a decrease in blood pressure. Additionally, histamine increases the heart rate through direct action on the heart, as well as via reflex mechanisms due to the fall in blood pressure.

What is the purpose of using propranolol in the experiment with isoprenaline?

Propranolol is used as a beta blocker to differentiate isoprenaline from other drugs. If isoprenaline is the drug in question, the graph will show a decrease in heart rate and blood pressure when propranolol is administered. This helps identify isoprenaline by blocking the beta receptors.

Why do meperidine (permin) and cimetidine (cement) have similar graphs in the experiment?

Both meperidine and cimetidine block histamine receptors, but they differ in which receptor they block (H1 vs H2). Their graphs are similar because both drugs have little to no effect on blood pressure and heart rate in the absence of histamine release, making them difficult to distinguish without further testing.

How can the antagonist of a drug help identify an unknown sample in the experiment?

By using the antagonist of a suspected drug, we can confirm the identity of the unknown sample. For example, if the unknown sample affects blood pressure and heart rate in a manner consistent with a specific drug, administering the corresponding antagonist will block its action, allowing us to identify the drug based on the change (or lack thereof) in the graph.