CB [058] Targets antihypertensive lecture B 2024-25

Course Overview

Instructor: Dr. Nada El-Ekiaby, Lecturer of Molecular PharmacologyTerm: 2024-2025, School of Medicine

Identify Blood Pressure RegulationUnderstand the various physiological mechanisms and sites involved in the complex regulation of blood pressure, including neural, hormonal, and renal influences.
Explore Targets for Therapeutic InterventionStudy and comprehend the primary targets for antihypertensive therapies, including their mechanisms of action and clinical implications.

Baroreceptors: Sensory receptors that detect changes in blood pressure and help regulate cardiovascular response.
Blood Volume Regulation: Mechanisms related to renal water reabsorption and natriuresis.
Renin-Angiotensin System: Key therapeutic targets include ACE inhibitors and Angiotensin receptor blockers that alter the effects of angiotensin II, notably in vascular contraction and fluid balance.
Peripheral Resistance: Drugs that reduce peripheral vascular resistance, including alpha-blockers, vasodilators, and calcium channel blockers.
Cardiac Output Intervention: Use of beta-blockers to decrease heart rate and contractility, thereby affecting cardiac output.
Sodium Excretion: The role of diuretics in promoting sodium loss and lowering blood volume.
Endothelial Autacoids: Key agents like Nitric Oxide (NO) and Endothelin-1 (ET-1) that play crucial roles in vascular function.

Blood VolumeFocus on modulating blood volume via diuretics and renal function.
Nervous Control of Cardiac Output and Peripheral ResistanceInvestigate how sympathetic nervous system activity impacts these cardiovascular parameters.
Humoral Control of Cardiac Output and Peripheral ResistanceDiscussion of the influence of circulating hormones on vascular tone and fluid dynamics.
Excitation-Contraction CouplingMechanisms affecting how cardiac muscle cells respond to electrical stimulation and influence contraction.

Diuretics
- Key role in altering sodium and water balance to manage hypertension effectively.
- Effective range for BP reduction: 10-15 mmHg.

Thiazide Diuretics:
- Examples: Hydrochlorothiazide (HCTZ), Chlorthalidone.
- Mechanism: Inhibit NaCl transport at the distal convoluted tubule (DCT), resulting in decreased Na+ and water reabsorption.
- Usage: Typically the first line for mild to moderate hypertension, especially to prevent strokes and heart failure.
Loop Diuretics:
- Example: Furosemide.
- Mechanism: Inhibit the Na/K/2Cl transporter in the thick ascending limb of the loop of Henle; leads to significant diuresis.
- Usage: Effective in severe hypertension, acute pulmonary edema, renal insufficiency, and specific cases of cardiac failure.
Potassium-Sparing Diuretics:3.1 Amiloride and Triamterene:
- Mechanism: Inhibit Na+ reabsorption and prevent K+ secretion in the collecting tubules.
- Usage: Often used in combination with other diuretics to mitigate hypokalemia risk.
3.2 Aldosterone Receptor Antagonists:
- Example: Spironolactone.
- Mechanism: Inhibits aldosterone action, reducing Na+ reabsorption and promoting K+ retention.
- Effect: Beneficial for cardiac function improvement, particularly in heart failure patients.

Centrally Acting agents: e.g., Clonidine and Methyldopa reduce sympathetic outflow and lower blood pressure effectively.
Ganglion-Blocking Agents: Largely obsolete due to their poor side effect profile and newer alternatives.
Norepinephrine Release Reducers: e.g., Guanethidine, rarely used today due to severe side effects.
Postsynaptic Adrenoreceptor Blockers:
- α1 Blockers: e.g., Prazosin, effective in treating hypertension and symptoms of benign prostatic hyperplasia.
- β-Blockers: Propranolol, Metoprolol, useful for multiple cardiovascular conditions, including arrhythmias and ischemic heart disease.

Function: Relax vascular smooth muscle, thereby decreasing systemic vascular resistance and lowering blood pressure.
Mechanisms:
- Release of Nitric Oxide: Seen with agents like Hydralazine.
- Calcium Influx Reduction: Achieved through calcium channel blockers.
- Potassium Channel Opening: Example includes Minoxidil.

ACE Inhibitors:
- Examples: Ramipril, Captopril; block the conversion of Angiotensin I to Angiotensin II, a potent vasoconstrictor, leading to reduced blood pressure.
Angiotensin II Receptor Blockers (ARBs):
- Examples: Valsartan, Losartan; selectively block AT1 receptors to prevent the effects of angiotensin II.

Thiazide Diuretics: Common side effects include urinary frequency, hyperuricemia (gout), glucose intolerance, hypokalemia, and hyponatremia.
Loop Diuretics: Similar effects as thiazides, but with added risks such as ototoxicity at higher doses.
ACE Inhibitors: Patients may experience cough, hypotension, and hyperkalemia; contraindicated in pregnancy due to teratogenic effects.
ARBs: Likely to have similar side effects as ACE inhibitors but with lower cough incidence; also carry teratogenic risk.
β-Blockers: Potential bronchospasm, fatigue, bradycardia, and heart block issues.
Direct Vasodilators and K+ Channel Activators: Can lead to salt retention and reflex tachycardia.

Lifestyle Modifications: Recommended as the first line for managing elevated BP thresholds through diet, exercise, and weight management.
Stage 1 Hypertension: Involves mainly thiazide diuretics for most patients, considering alternatives like ACE inhibitors, ARBs, β-blockers, or calcium channel blockers as needed.
Stage 2 Hypertension: Emphasizes a combination therapy approach often including two drug classes for optimal blood pressure control.
Goal: Persistent optimization of dosages or introduction of additional agents until achieving target blood pressure goals.