Exercise 6: Cardiovascular Physiology: Activity 4: Examining the Effects of Chemical Modifiers on Heart Rate Lab Report Pre-lab Quiz Results You scored 100% by answering 4 out of 4 questions correctly. 1. The parasympathetic nervous system releases __________ to affect heart rate. You correctly answered: d. acetylcholine 2. A cholinergic drug that worked the same as acetylcholine would You correctly answered: c. be an agonist and decrease heart rate. 3. Norepinephrine affects the heart rate by You correctly answered: a. increasing the rate of depolarization and increasing the frequency of action potentials. 4. The __________ receptor binds norepinephrine and epinephrine. You correctly answered: b. ß-1 adrenergic

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Experiment Results Predict Question: Predict Question 1: Pilocarpine is a cholinergic drug, an acetylcholine agonist. Predict the effect that pilocarpine will have on heart rate. Your answer : b. Pilocarpine will decrease heart rate. Predict Question 2: Atropine is another cholinergic drug, an acetylcholine antagonist. Predict the effect that atropine will have on heart rate. Your answer : a. Atropine will increase heart rate. Stop & Think Questions: Which of the following is true of epinephrine? You correctly answered: c. It increases the heart rate and mimics the sympathetic nervous system. The final chemical modifier we will look at is digitalis (also known as digoxin and digitoxin and derived from the foxglove plant). Individuals with weakened hearts need to allow maximum time for venous return and increased stroke volume and would therefore most likely benefit from You correctly answered: c. increased force of contraction and decreased heart rate Experiment Data: Solution ---Epinephrine Pilocarpine Atropine Digitalis Heart Rate 61 81 46 71 42

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Post-lab Quiz Results You scored 100% by answering 4 out of 4 questions correctly. 1. Pilocarpine decreased the heart rate. Typical of cholinergic agonists, it You correctly answered: b. decreased the frequency of action potentials. 2. The effect of atropine was to You correctly answered: c. mimic the sympathetic nervous system. 3. The modifiers tested that decrease the heart rate were You correctly answered: c. digitalis and pilocarpine. 4. To increase the heart rate, the best choices would be You correctly answered: b. epinephrine and atropine.

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Review Sheet Results 1. Describe the effect that pilocarpine had on the heart and why it had this effect. How well did the results compare with your prediction? Your answer: Pilocarpine is a cholinergic drug, an acetylcholine agonist released by the parasympathetic nerve fibers. The acetylcholine decreases the action potential by binding up the muscarinic cholinergic receptors. This would decrease the heart rate. It went from a normal rate of 61 to 46. The results agreed with my prediction. 2. Atropine is an acetylcholine antagonist. Does atropine inhibit or enhance the effects of acetylcholine? Describe your results and how they correlate with how the drug works. How well did the results compare with your prediction? Your answer: Since atropine is an acetlycholine (ACh) antagonist, it will inhibit the effects of ACh, therefore raising the heart rate. Atropine caused the base heart rate to go from 61 to 71 showing that it worked by antagonizing ACh. These results compared well with my prediction. 3. Describe the benefits of administering digitalis. Your answer: Digitalis drugs are used to enhance a weak heart in congestive heart failure. People with a bad heart need to have maximum time for the venous return and increased stroke volume would benefit from increased force of contraction and decreased heart rate caused by the administration of digitalis drugs. 4. Distinguish between cholinergic and adrenergic chemical modifiers. Include examples of each in your discussion. Your answer: Cholingeric and adrenergic modifiers inhibit, mimic, or enhance the action of acetylcholine in the body. Pilocarpine is a direct acting cholinergic agonist that decreases the heart rate by directly acting on the receptor the same as acetylcholine. Atropine is a cholingeric antagonist that blocks the acetylcholine receptor increasing the heart rate. Epinephrine is an adrenergic agonist and binds to adrenergic receptor like B1, B2, and Alpha1 and increases heart rate. This mimics effect of the sympathetic nervous system.

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