Aim: To study the effects of various drugs on dog blood pressure (BP) and heart rate. Reference: Kulkarni SK. Handbook of Experimental Pharmacology. 4th ed. New Delhi: Vallabh Prakashan; 2012. pp. 75–82. Requirements: Animal / Simulation Model • Anesthetized dog preparation (or suitable computer-assisted learning/CAL simulation software model) Apparatus • Experimental table / animal board • Tracheal cannula • Arterial cannula (carotid/femoral artery) • Venous cannula (femoral/jugular vein) • Mercury manometer or pressure transducer with data acquisition system • Kymograph / Smoked drum (or digital recording system) • Surgical instruments (scalpel, forceps, scissors, arterial forceps, hemodynamics clamps) • Syringes and needles • Heparinized normal saline solution Drugs • Adrenaline (Stock solution: 10 μg/mL) • Noradrenaline (Stock solution: 10 μg/mL) • Isoprenaline (Stock solution: 10 μg/mL) • Acetylcholine (Stock solution: 10 μg/mL) • Histamine (Stock solution: 10 μg/mL) • Atropine (Stock solution: 1 mg/mL) • Propranolol (Stock solution: 1 mg/mL) • Phentolamine (Stock solution: 1 mg/mL) Physiological Solution • Heparinized Normal Saline (0.9% NaCl with 10 units/mL heparin) Principle: Blood pressure (BP) is determined by cardiac output (CO) and peripheral vascular resistance (PVR): Autonomic drugs modulate cardiovascular parameters by acting on specific adrenergic and cholinergic receptors located on the myocardium and blood vessels: • Adrenaline (Epinephrine): Acts on , , and receptors. Low doses decrease mean arterial pressure due to -mediated vasodilation. Moderate to high doses produce a biphasic response: an initial sharp rise in BP ( vasoconstriction and cardiac stimulation) followed by a secondary drop below baseline ( vasodilation, Dale's vasomotor reversal). • Noradrenaline (Norepinephrine): Acts predominantly on and receptors with minimal activity. Produces a marked rise in systolic and diastolic BP via intense vasoconstriction () alongside a reflex bradycardia (vagal reflex). • Isoprenaline (Isoproterenol): Pure -agonist ( and ). Decreases diastolic and mean BP ( vasodilation) while increasing heart rate ( direct positive chronotropism). • Acetylcholine: Acts on vascular receptors (inducing EDRF/NO release) and cardiac receptors. Causes transient hypotension and bradycardia. • Histamine: Acts on and receptors on vascular smooth muscle, producing marked vasodilation and fall in BP. • Antagonists (Atropine, Phentolamine, Propranolol): Block specific receptor pathways, thereby selectively altering or abolishing the responses of subsequent agonist challenges. Procedure: 1. Anesthetize the animal (or set up the simulated dog model) using pentobarbital sodium (30 mg/kg i.v.). 2. Secure the animal on the operating table in a supine position. 3. Perform a tracheostomy and insert a tracheal cannula to maintain clear airway respiration. 4. Cannulate the femoral or jugular vein for intravenous drug administration. 5. Cannulate the common carotid or femoral artery and connect it to a mercury manometer or pressure transducer filled with heparinized saline to record arterial BP and heart rate. 6. Record baseline blood pressure (systolic, diastolic, mean) and heart rate. 7. Inject 0.1–0.2 mL of Adrenaline intravenously, flush with saline, and record changes in BP and heart rate. Allow the parameters to return to baseline. 8. Inject Noradrenaline, Isoprenaline, Acetylcholine, and Histamine sequentially, ensuring complete recovery to baseline baseline between doses. 9. Administer Atropine (1 mg/kg i.v.) to block muscarinic receptors; wait 10 minutes, then re-inject Acetylcholine to observe the blockade of response. 10. Administer Phentolamine (1 mg/kg i.v.) to block -adrenergic receptors; wait 10 minutes, then re-inject Adrenaline to demonstrate Dale's vasomotor reversal. 11. Administer Propranolol (1 mg/kg i.v.) to block -adrenergic receptors; wait 10 minutes, then re-test Isoprenaline and Adrenaline. 12. Label and fix tracings or export digital hemodynamic recordings for analysis. Observation Table 1. Effect of Various Drugs on Dog Blood Pressure and Heart Rate Drug / Agent Dose Blood Pressure (BP) Heart Rate (HR) Vasomotor / Cardiac Effect Adrenaline 1–2 μg/kg Biphasic (Initial ↑, then ↓) ↑ (Direct) / Variable activation Noradrenaline 1–2 μg/kg Marked ↑ (Systolic & Diastolic) ↓ (Reflex Bradycardia) activation Isoprenaline 1–2 μg/kg Decreased (↓ Diastolic) Marked ↑ Direct activation Acetylcholine 1–2 μg/kg Transient ↓ ↓ Direct activation Histamine 1–2 μg/kg Marked ↓ Reflex ↑ activation After Atropine + Acetylcholine 1 mg/kg + 2 μg/kg No change / Blocked No change Muscarinic () Blockade After Phentolamine + Adrenaline 1 mg/kg + 2 μg/kg Pure Drop (↓ Only) ↑ Dale's Vasomotor Reversal ( blocked) After Propranolol + Isoprenaline 1 mg/kg + 2 μg/kg No drop / Blocked Blocked Blockade Symbols: ↑ = Increase; ↓ = Decrease Results: Drug / Interaction Effect on BP Effect on Heart Rate Primary Mechanism Adrenaline Biphasic response Increased Combined stimulation Noradrenaline Vasopressor response Reflex decrease Selective stimulation Isoprenaline Depressor response Increased Selective stimulation Acetylcholine Depressor response Decreased Muscarinic stimulation () Atropine + Acetylcholine Blocked response Blocked response Competitive blockade of receptors Phentolamine + Adrenaline Reversal to pure fall Increased -blockade unmasking vasodilation Conclusion: The experimental model successfully demonstrated the characteristically distinct actions of autonomic drugs on mammalian systemic blood pressure and heart rate. Adrenaline exhibited a classic biphasic blood pressure response due to simultaneous activation of vasoconstrictor receptors and vasodilator receptors. Noradrenaline produced a steep vasopressor response () accompanied by reflex bradycardia mediated by baroreceptors. Isoprenaline produced a depressor effect () along with direct positive chronotropism (). Acetylcholine caused hypotension and bradycardia via muscarinic activation, which was effectively blocked by the muscarinic antagonist Atropine. Pretreatment with the -blocker Phentolamine unmasked the -mediated vasodilator action of Adrenaline, successfully demonstrating Dale's vasomotor reversal. Precautions: 1. Maintain an adequate and uniform plane of anesthesia throughout the surgical and recording procedures. 2. Ensure tracheal cannula remains free of mucus obstruction to prevent asphyxia-induced BP fluctuations. 3. Keep arterial and venous cannulae patently clear using heparinized saline to avoid clot formation. 4. Administer drugs slowly in small, precise volumetric doses flushed with normal saline. 5. Allow sufficient time between drug administrations for BP and heart rate to completely return to baseline. 6. Calibrate pressure transducers or mercury manometers accurately prior to recording baseline values. Make it short