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Effect of drugs on frog’s heart

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This presentation deals with the in-depth analysis of various cardiac stimulants & depressants both directly & indirectly acting on frog's heart. Also, includes a nice quiz, a good exercise for the grey cells of the brain at the end of the presentation.

This presentation deals with the in-depth analysis of various cardiac stimulants & depressants both directly & indirectly acting on frog's heart. Also, includes a nice quiz, a good exercise for the grey cells of the brain at the end of the presentation.

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Effect of drugs on frog’s heart

  1. 1. CAL  Effect of drugs on frog’s heart
  2. 2. Following parameters noted 1. Force of contraction  amplitude (N, ↑, ↓) 2. Tone (N, ↑, ↓) 3. Heart rate (bpm)
  3. 3. Addition of unknown drug (UD) to frog’s heart ↓ ↓ ↑ HR, tone, amplitude ↓ HR, tone, amplitude ↓ ↓ UD  Cardiac stimulant UD  Cardiac depressant ↓ ↓ Ppnl (0.2 ml) inj. foll. By UD Atr (0.2 ml) inj. foll. by UD ↓ ↓ ↓ ↓ No effect ↑ tone No effect ↓ tone ↓ ↓ ↓ ↓ UD - Indir. UD - Directly UD – Indir. UD -Directly Acting cs acting cs acting cd acting cd (E,NE, Iso) (CaCl2) (Ach) (KCl)
  4. 4. Regulation of the heart Dominant tone = parasympathetic Sympathetic Increases heart rate and contractility via beta-1 and 2 (primarily beta-1) Parasympathetic Decreases heart rate and atrial contractility via M2
  5. 5. PREDOM
  6. 6. 1. Ach Cardiac effects  ↓ impulse formation in SAN by ↓ the rate of diastolic depolarization (↓ HR) & ↑ PR interval (Time from SAN to AVN) 2. Atr Cardiac eff.  ↑ HR & AV conduction velocity by blocking the effects of the vagus nerve on sa,av • Low i.v. atropine  paradoxical slowing of HR (stimulation of the vagal motor nucleus in the brain stem). After full dose  heart rate ↑
  7. 7. CVS eff. Of NE, E, Isoprenaline • NE  Activation of α1 receptors (V.c. & ↑ TPR) Reflex bradycardia if blood pressure increases sufficiently to activate the baroreceptor reflex • E  ↑ SBP but can ↑ or ↓ DBP • Isoproterenol  Activates β1 and β2 receptors • Propranolol  Blockade of β1 receptors
  8. 8. Baroreceptor reflex
  9. 9. Dopamine • Low doses (< 2 μg/kg per min)  D1 dopaminergic receptors in renal, mesenteric, and coronary vascular beds. (vasodilation) • Moderate dose (2–10 μg/kg per min)  β1 recept. • Higher dose (10 μg/kg per min)  α1 receptors
  10. 10. Adrenaline Uses (ABCD) 1. Anaphylactic shock (DOC)  0.5 mg (0.5 ml of 1 in 1000 solution for adult) i.m. 2. Bronchial asthma 3. Cardiac arrest  10 ml of 1:10000 i.v. 4. Control of local bleeding  Adr 1 in 10,000 5. During LA combined with Lignocaine (1:50,000 or 1:2,00,000)
  11. 11. Acetylcholine • Choline ester of acetic acid • Uses 1. During cataract surgery (Miosis) NO topical 2. Diagnostic coronary angiography  intracoronary injection to cause coronary artery spasm 3. Vasospastic angina pectoris, however, intracoronary injection of acetylcholine can provoke a localized vasoconstrictive response, and this helps establish the diagnosis of vasospastic angina
  12. 12. Atropine & Scopolamine (t.a.) • t1/2  2 hrs (oral route) • After topical ocular administration, they have longer-lasting effects because they bind to pigments in the iris that slowly release the drugs. • People with darker irises bind more atropine and experience a more prolonged effect than do people with lighter irises. The ocular effects gradually subside over several days. • “dry as a bone, blind as a bat, red as a beet, and mad as a hatter.” Atr. toxicity
  13. 13. Effects • Ocular eff.  Myd. + cycloplegia • Cardiac eff.  ↑ HR & AV conduction velocity by blocking the effects of the vagus nerve on SAN,AVN Low i.v. atropine  paradoxical slowing of HR (stimulation of the vagal motor nucleus in the brain stem). After full dose  heart rate ↑ • Resp. tract eff.  bronchial smooth muscle relaxation and bronchodilation, inhibitors of secretions in the upper and lower respiratory tract.
  14. 14. Indications • Ocular Indications  mydriasis (facilitate peripheral retina), cycloplegia (refractive errors), iritis and cyclitis (↓ muscle spasm and pain) • Cardiac Indications  Sinus bradycardia after MI. AV block to ↑ AV conduction velocity • Respiratory Tract Indications  ↓ salivary and respiratory secretions & prevent airway obstruction in patients who are receiving general anaesthetics. Glycopyrrolate is often used for this purpose today
  15. 15. • GIT Indications  Relieve intestinal spasms & pain • UT indications  Relieve urinary bladder spasms in persons with overactive bladder. • CNS Indications  A transdermal formulation of scopolamine can be used to prevent motion sickness (blocking Ach neurotransmission from the vestibular apparatus to the vomiting center in the brain stem). Also, PD. • Other Indications 1. Prevent muscarinic side effects when chE inhibitors are given to patients with myasthenia gravis. 2. Reverse the muscarinic effects of cholinesterase inhibitor overdose.
  16. 16. Atropine Uses (ATROPA) 1. As mydriatic-cycloplegic in refraction error testing, fundoscopy, iridocyclitis 2. Traveller’s diarrhea 3. Rapid onset mushroom poisoning 4. Organophospohorous poisoning 5. Preanaesthetic medication 6. Arrhythmias (brady-arrhythmias)
  17. 17. Propranolol (Uses  THAPPAD) 1. Thyrotoxicosis & Tremors 2. HTN & Hypertrophic cardiomyopathy 3. Angina & Acute MI 4. Prophylaxis of migraine 5. Phaeochromocytoma (along with alpha blockers) 6. Anxiety & Arrhythmias 7. Dissecting aortic aneurysm 8. Digitalis toxicity
  18. 18. MUSCARINIC effects (OP poisoning) M  Miosis U  Urination S  Secretions ↑ (salivation, lacrimation, sweating) C  Cardiac contraction & conduction slows A  Abdominal cramps R  Redn. In i.o.t. esp. in glaucoma I  ↑ GI motility N  NO dependent vasodilatation I  Inc. secretion from GIT & tracheobronchial tract C  Constriction of tracheobronchial tract
  19. 19. Adverse effects of Atropine (DHATURA) 1. Dry mouth, difficulty in swallowing & speaking 2. Hot dry skin & hypotension 3. Accommodation paralysis (blurring of near vision) 4. Tachycardia 5. Urinary retention & fecal retention (constipation) 6. Respiratory depression 7. Ataxia & acute congestive glaucoma may precipitate
  20. 20. Adverse effects of beta blockers (BBC Loses Viewers in Rochedale) • Bradycardia • Bronchoconstriction • Claudication • Lipids (profile altered) • Vivid dreams & nightmares • Negative ionotropic action • Reduced sensitivity to hypoglycemia
  21. 21. Contraindications of Propranolol • Don’t Prescribe Him Propranolol 1. Diabetes mellitus 2. Pulmonary diseases (Asthma, COPD) 3. Heart block, bradycardia 4. Prinzmetal’s angina 5. Peripheral vascular disease
  22. 22. Review Questions
  23. 23. Q.1. 1. A 3-year-old child has swallowed the contents of 2 bottles of a nasal decongestant whose primary ingredient is a potent, selective α-adrenoceptor agonist drug. Which of the following is a sign of α- receptor activation that may occur in this patient? (A) Bronchodilation (B) Cardiac acceleration (tachycardia) (C) Pupillary dilation (mydriasis) (D) Renin release from the kidneys (E) Vasodilation of the splanchnic vessels
  24. 24. Q.2. Ms Green is a 60-year-old woman with poorly controlled hypertension of 170/110 mm Hg. She is to receive minoxidil. The active metabolite of minoxidil is a powerful arteriolar vasodilator that does not act on autonomic receptors. Which of the following effects will be observed if no other drugs are used? (A) Tachycardia and increased cardiac contractility (B) Tachycardia and decreased cardiac output (C) Decreased mean arterial pressure and decreased cardiac contractility (D) Decreased mean arterial pressure and increased salt and water excretion by the kidney (E) No change in mean arterial pressure and decreased cardiac contractility
  25. 25. Q.3. Full activation of the sympathetic nervous system, as in the fight-or-flight reaction, may occur during maximal exercise. Which of the following effects is likely to occur? (A) Bronchoconstriction (B) Increased intestinal motility (C) Decreased renal blood flow (D) Miosis (E) Decreased heart rate (bradycardia)
  26. 26. Q.4. Nicotinic receptor sites do not include which one of the following sites? (A) Bronchial smooth muscle (B) Adrenal medullary cells (C) Parasympathetic ganglia (D) Skeletal muscle end plates (E) Sympathetic ganglia
  27. 27. Q.5. Which one of the following is the neurotransmitter agent normally released in the sinoatrial node of the heart in response to a blood pressure increase? (A) Acetylcholine (B) Dopamine (C) Epinephrine (D) Glutamate (E) Norepinephrine
  28. 28. Q.6. A 30-year-old woman undergoes abdominal surgery. In spite of minimal tissue damage, complete ileus (absence of bowel motility) follows, and she complains of severe bloating. She also finds it difficult to urinate. Mild cholinomimetic stimulation with bethanechol or neostigmine is often effective in relieving these complications of surgery. Neostigmine and bethanechol in moderate doses have significantly different effects on which one of the following? (A) Gastric secretion (B) Neuromuscular end plate (C) Salivary glands (D) Sweat glands (E) Ureteral tone
  29. 29. Q.7. Ms Brown has been treated for myasthenia gravis for several years. She reports to the emergency department complaining of recent onset of weakness of her hands, diplopia, and difficulty swallowing. She may be suffering from a change in response to her myasthenia therapy, that is, a cholinergic or a myasthenic crisis. Which of the following is the best drug for distinguishing between myasthenic crisis (insufficient therapy) and cholinergic crisis (excessive therapy)? (A) Atropine (B) Edrophonium (C) Physostigmine (D) Pralidoxime (E) Pyridostigmine
  30. 30. Q.8. A crop duster pilot has been accidentally exposed to a high concentration of a highly toxic agricultural organophosphate insecticide. If untreated, the cause of death from such exposure would probably be (A) Cardiac arrhythmia (B) Gastrointestinal bleeding (C) Heart failure (D) Hypotension (E) Respiratory failure
  31. 31. Q.9. Actions and clinical uses of muscarinic cholinoceptor agonists include which one of the following? (A) Bronchodilation (asthma) (B) Improved aqueous humor drainage (glaucoma) (C) Decreased gastrointestinal motility (diarrhea) (D) Decreased neuromuscular transmission and relaxation of skeletal muscle (during surgical anesthesia) (E) Increased sweating (fever)
  32. 32. Q.10. Which of the following is the primary second- messenger process in the contraction of the ciliary muscle when focusing on near objects? (A) cAMP (cyclic adenosine monophosphate) (B) DAG (diacylglycerol) (C) Depolarizing influx of sodium ions via a channel (D) IP3 (inositol 1,4,5-trisphosphate) (E) NO (nitric oxide)
  33. 33. Q.11. Probable signs of atropine overdose include which one of the following? (A) Gastrointestinal smooth muscle cramping (B) Increased heart rate (C) Increased gastric secretion (D) Pupillary constriction (E) Urinary frequency
  34. 34. Q.12. Accepted therapeutic indications for the use of antimuscarinic drugs include all of the following except (A) Atrial fibrillation (B) Motion sickness (C) Parkinson’s disease (D) Postoperative bladder spasm (E) To antidote parathion poisoning
  35. 35. Q.13. A 7-year-old boy with a previous history of bee sting allergy is brought to the emergency department after being stung by 3 bees. If this child has signs of anaphylaxis, what is the treatment of choice? (A) Diphenhydramine (an antihistamine) (B) Ephedrine (C) Epinephrine (D) Methylprednisolone (a corticosteroid) (E) Phenylephrine
  36. 36. Q.14. A 65-year-old woman with long-standing diabetes mellitus is admitted to the ward from the emergency department, and you wish to examine her retinas for possible changes. Which of the following drugs is a good choice when pupillary dilation—but not cycloplegia—is desired? (A) Isoproterenol (B) Norepinephrine (C) Phenylephrine (D) Pilocarpine (E) Tropicamide
  37. 37. Q.15.An anesthetized dog is prepared for recording blood pressure and heart rate in a study of a new blocking drug. Results show that the new drug prevents the tachycardia evoked by isoproterenol? Which of the following standard agents does the new drug most resemble? (A) Atropine (B) Hexamethonium (C) Phentolamine (an α blocker) (D) Physostigmine (E) Propranolol (a β blocker)
  38. 38. Q.16. Your new 10-year-old patient has asthma, and you decide to treat her with a β2 agonist. In considering the possible drug effects in this patient, you would note that β2 stimulants frequently cause (A) Direct stimulation of renin release (B) Hypoglycemia (C) Increased cGMP (cyclic guanine monophosphate) in mast cells (D) Skeletal muscle tremor (E) Vasodilation in the skin
  39. 39. Q.17. A patient is to receive epinephrine. She has previously received an adrenoceptor-blocking agent. Which of the following effects of epinephrine would be blocked by phentolamine but not by metoprolol? (A) Cardiac stimulation (B) Increase of cAMP in fat (C) Mydriasis (D) Relaxation of bronchial smooth muscle (E) Relaxation of the uterus
  40. 40. Q.18. When given to a patient, phentolamine blocks which one of the following? (A) Bradycardia induced by phenylephrine (B) Bronchodilation induced by epinephrine (C) Increased cardiac contractile force induced by norepinephrine (D) Miosis induced by acetylcholine (E) Vasodilation induced by isoproterenol
  41. 41. Q.19. A 56-year-old man has hypertension and an enlarged prostate, which biopsy shows to be benign prostatic hyperplasia. He complains of urinary retention. Which of the following drugs would be the most appropriate initial therapy? (A) Albuterol (B) Atenolol (C) Metoprolol (D) Prazosin (E) Timolol
  42. 42. Q.20. Which of the following agents does the new drug most closely resemble? (A) Atenolol (B) Atropine (C) Labetalol (D) Phenoxybenzamine (E) Propranolol
  43. 43. Thank you

Notas del editor

  • 3 chambered  2 atria + 1 ventricle SVC & IVC open into sinus venosus
    Venous blood : Sinus venosus  RA  Ventricle
    Arterial blood : LA  Ventricle
    Ventricle pumps mixed blood  Aorta
    Aorta has spiral valve that directs arterial blood to body & venous blood to lungs through pulm. Art.
    NO valves & NO conducting tissue !!

  • Start with 0.1 ml. If sufficient response is not there, increase dose to 0.2 ml
  • The increased systolic pressure results partly from an increased heart rate and cardiac output. The effect on diastolic pressure depends on the relative stimulation of α1- and β2-adrenoceptors. which mediate vasoconstriction and vasodilation, respectively. Lower doses of epinephrine produce greater stimulation of β2-receptors than α1-receptors, especially in the vascular beds of skeletal muscle, thereby causing vasodilation and decreasing diastolic blood pressure. Higher doses produce
    more vasoconstriction throughout the body and can increase both diastolic and systolic pressure. And produces vasodilation and cardiac stimulation. It usually
    lowers the diastolic and mean arterial pressure, but it can increase the systolic pressure by increasing the heart rate and contractility. Its potent chronotropic effect can cause tachycardia and cardiac arrhythmias. For this reason, an alternative drug (e.g., dobutamine) is usually administered to increase cardiac output in cases of heart failure. Dobutamine selectively increases myocardial contractility and stroke volume while producing a smaller increase in heart rate.
    reduces sympathetic stimulation of the heart, causing a negative chronotropic, inotropic, and dromotropic effect. Because the β-blockers reduce cardiac output and blood pressure (see Fig. 9-2), they can be used to treat arterial hypertension
  • The baroreceptor reflx. A, Increased arterial pressure activates stretch receptors in the aortic arch and carotid sinus. B, Receptor activation initiates afferent impulses to the brain stem vasomotor center (VMC). C, Via solitary tract fiers, the VMC activates the vagal motor nucleus, which increases vagal (parasympathetic) outflw and slows the heart. At the same time, the VMC reduces stimulation of spinal intermediolateral neurons that activate sympathetic preganglionic fiers, and this decreases sympathetic stimulation of the heart and blood vessels. By this mechanism, drugs that increase blood pressure produce reflex bradycardia. Drugs that reduce blood pressure attenuate this response and cause reflex tachycardia.
  • Vasomotor reversal of Dale. Comparison of the cardiovascular effects of four catecholamines when a low dose of each drug is given by intravenous infusion. Arrows
    indicate when the infusion was started and stopped. The blood pressure recordings show systolic, diastolic, and mean arterial pressure. Peripheral resistance
    is expressed on an arbitrary scale, ranging from 0 to 4 units. The reflex mechanism, adrenoceptors (α1, β1, and β2), or dopamine (D1) receptors responsible
    for changes in the heart rate and peripheral resistance are illustrated. Norepinephrine increases peripheral resistance and blood pressure, and this leads to
    reflex bradycardia. Epinephrine increases heart rate while reducing peripheral resistance, and the mean arterial blood pressure increases slightly. Isoproterenol
    increases heart rate but significantly lowers peripheral resistance, and the mean arterial pressure declines. Dopamine increases heart rate (and increases
    cardiac output) while lowering vascular resistance, and the mean arterial pressure increases.
    Vasomotor reversal of Dale
  • The heart is innervated by vagal and sympathetic fibers. The right vagus nerve primarily innervates the SA node, whereas the left vagus innervates the AV node; however, there can be significant overlap in the anatomical distribution. Atrial muscle is also innervated by vagal efferents, whereas the ventricular myocardium is only sparsely innervated by vagal efferents. Sympathetic efferent nerves are present throughout the atria (especially in the SA node) and ventricles, including the conduction system of the heart.
    Sympathetic stimulation of the heart increases heart rate (positive chronotropy), inotropy and conduction velocity (positive dromotropy), whereas parasympathetic stimulation of the heart has opposite effects. Sympathetic and parasympathetic effects on heart function are mediated by beta-adrenoceptors and muscarinic receptors, respectively.
  • The solution also can be used in other types of ophthalmic surgery that require rapid and complete miosis. Topical ocular administration of acetylcholine is not effective, because acetylcholine is hydrolyzed by corneal cholinesterase before it can penetrate to the iris and ciliary muscle.
  • E. Respiratory failure, from neuromuscular paralysis or CNS depression, is the most important cause of acute deaths in cholinesterase inhibitor toxicity. The answer is E.
  • Tremor is a common β2 effect. Blood vessels in the skin have almost exclusively α (vasoconstrictor) receptors. Stimulation of renin release is a β1 effect. Beta2 agonists cause hyperglycemia. The answer is D.
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