Organic Molecules, Human, Proteins & Amino Acids, Peptides

Angiotensin

23
May

Angiotensin is a family of peptide hormones critical for regulating blood pressure, fluid balance, and cardiovascular function. Derived from the precursor protein angiotensinogen, it is not consumed in the diet but synthesized endogenously, relying on dietary amino acids and nutrients. This article provides a clear, engaging, and scientifically accurate overview of angiotensin, empowering you to understand its properties, biological importance, and health implications.

What Is Angiotensin?

Chemical Nature and Classification

  • Molecular Formula: Varies by form (e.g., angiotensin II: C₅₀H₇₁N₁₃O₁₂, ~1 kDa).
  • Classification: Peptide hormones, part of the renin-angiotensin-aldosterone system (RAAS).
  • Structure:
    • Derived from angiotensinogen, a 452-amino acid glycoprotein (~60 kDa) produced in the liver.
    • Key forms:
      • Angiotensin I: 10-amino acid peptide (inactive).
      • Angiotensin II: 8-amino acid peptide (primary active form).
      • Angiotensin III and IV: Shorter peptides with lesser roles.
    • Angiotensin II sequence: Asp-Arg-Val-Tyr-Ile-His-Pro-Phe, with key amino acids (e.g., arginine, tyrosine) from dietary or endogenous pools.
  • Properties: Soluble in plasma, short-lived (half-life ~1–2 minutes), and rapidly cleaved by enzymes. Synthesized via enzymatic cleavage of angiotensinogen, not consumed in the diet. Critical for vasoconstriction, aldosterone release, and sodium retention.

Biological Role and Mechanism of Action

How Angiotensin Functions in the Body

  • Blood Pressure Regulation:
    • Angiotensin II causes vasoconstriction, increasing blood pressure:
Angiotensin II → AT1 Receptors → Vascular Smooth Muscle Contraction
  • Stimulates aldosterone release, promoting sodium and water retention:
Angiotensin II → Adrenal Cortex → Aldosterone → Sodium Reabsorption
  • Fluid and Electrolyte Balance:
    • Enhances thirst and antidiuretic hormone (ADH) release, conserving water:
Angiotensin II → Hypothalamus → Thirst + ADH Secretion
  • Cardiovascular Function:
    • Promotes cardiac and vascular remodeling in chronic activation (e.g., hypertrophy):
Angiotensin II → Fibroblast Activation → Tissue Remodeling
  • Synthesis:
    • Produced via the RAAS pathway:
Angiotensinogen (Liver) → Angiotensin I (Renin, Kidneys) → Angiotensin II (ACE, Lungs)
  • Requires dietary protein (0.8 g/kg/day) for angiotensinogen synthesis, plus zinc (8–11 mg/day) and vitamin B6 (1.3–2 mg/day) for enzyme function (e.g., renin, ACE).
  • Metabolism:
    • Rapidly degraded by peptidases (e.g., angiotensinases) in plasma and tissues:
Angiotensin II → Inactive Peptides → Excretion
  • Provides negligible energy (~4 kcal/g indirectly via amino acid catabolism).

Physiological Importance

  • Maintains blood pressure and fluid homeostasis, critical for survival during dehydration or hemorrhage.
  • Supports kidney function by regulating glomerular filtration.
  • Influences cardiovascular health, with chronic overactivation linked to hypertension and heart disease.

Dietary Sources and Relevance to Angiotensin Production

No Direct Dietary Angiotensin

  • Angiotensin is not consumed in food; synthesized from angiotensinogen, which relies on dietary amino acids and nutrients.
  • Key Nutrients for Angiotensin Synthesis:
    • Protein-Rich Foods (50–70 g/day for angiotensinogen):
      • Meat, poultry (beef, chicken: 20–30 g protein/100 g).
      • Fish (salmon, tuna: 20–25 g protein/100 g).
      • Eggs (6–7 g protein/egg).
      • Dairy (cheese, yogurt: 5–10 g protein/100 g).
      • Plant-based: Soy, lentils, quinoa (5–15 g protein/100 g).
    • Supporting Micronutrients:
      • Zinc (8–11 mg/day, e.g., oysters, pumpkin seeds) for angiotensin-converting enzyme (ACE) activity.
      • Vitamin B6 (1.3–2 mg/day, e.g., chickpeas, bananas) for amino acid metabolism.
      • Sodium (1.5–2.3 g/day, e.g., salted foods) influences RAAS activation.
      • Potassium (2.6–3.4 g/day, e.g., bananas, spinach) modulates aldosterone effects.
    • Energy Sources: Carbohydrates/fats (25–35 kcal/kg/day) spare amino acids for synthesis.

Processed Sources

  • Medical Context:
    • No direct angiotensin supplements; RAAS-modulating drugs (e.g., ACE inhibitors, ARBs) are used clinically.
  • Supplements:
    • Protein powders (whey, plant-based: 20–30 g protein/serving).
    • Multivitamins (2–5 mg zinc, 1–2 mg B6).
    • Electrolyte supplements (sodium, potassium: 0.5–1 g/serving).
  • Functional Foods:
    • Fortified shakes with protein/zinc (10–20 g protein, 1–2 mg zinc/serving).

Bioavailability

  • Amino acids: ~90–95% bioavailability, absorbed in small intestine for angiotensinogen synthesis.
  • Zinc: 20–40% bioavailability, enhanced by animal proteins, reduced by phytates (grains).
  • Angiotensin peptides are not absorbed intact; synthesized and degraded in vivo.

Health Benefits and Potential Risks

Supported Health Benefits

  • Blood Pressure Stability:
    • Maintains blood pressure during stress (e.g., dehydration, hemorrhage), preventing shock (normal RAAS activity raises BP by 10–20 mmHg acutely).
  • Fluid Homeostasis:
    • Ensures hydration and electrolyte balance (e.g., angiotensin II increases water retention by 10–15% via ADH/aldosterone).
  • Kidney Function:
    • Regulates glomerular filtration rate, supporting renal health (e.g., RAAS maintains GFR within 10% during low BP).
  • Nutrient Delivery:
    • Protein-rich foods (e.g., fish, soy) provide amino acids, zinc, and omega-3s.

Health Risks

  • Overactive RAAS (Excessive Angiotensin II):
    • Causes: High sodium intake, stress, or renal artery stenosis.
    • Effects: Hypertension, heart failure, kidney damage (e.g., chronic angiotensin II elevation increases BP by 20–30 mmHg, raising cardiovascular risk by 15–25%).
    • Management: Low-sodium diet (1.5–2.3 g/day), ACE inhibitors (e.g., lisinopril), or ARBs (e.g., losartan).
  • Low RAAS Activity:
    • Causes: ACE inhibitors, adrenal insufficiency, or low sodium intake.
    • Effects: Hypotension, dehydration, electrolyte imbalance (e.g., low angiotensin II may drop BP by 10–15 mmHg, risking dizziness).
    • Management: Adjust medications, ensure sodium/potassium balance.
  • Allergic Reactions:
    • Rare, but protein-rich foods (e.g., eggs, soy) may trigger allergies.
  • Medical Conditions:
    • Hypertension: RAAS overactivity; manage with diet (DASH: low sodium, high potassium) and drugs.
    • Heart Failure: Excessive angiotensin II promotes remodeling; use ACE inhibitors/ARBs.
    • Kidney Disease: RAAS dysregulation; monitor protein (0.8–1.2 g/kg/day) and electrolytes.
  • Drug Interactions:
    • ACE Inhibitors/ARBs: Reduce angiotensin II, lowering BP (monitor for hypotension).
    • Diuretics: Enhance RAAS activation, increasing angiotensin II (monitor electrolytes).
    • NSAIDs: May impair RAAS, reducing kidney perfusion (use cautiously).

Recommended Daily Intake and Supplementation Guidelines

No Direct Angiotensin Requirement

  • Angiotensin is not consumed; synthesis depends on angiotensinogen and RAAS activation.
  • Recommended Nutrient Intakes (NIH):
    • Protein: 0.8 g/kg/day (~50–70 g/day for 70 kg adult).
    • Zinc: 8–11 mg/day.
    • Vitamin B6: 1.3–2 mg/day.
    • Sodium: 1.5–2.3 g/day (DASH diet recommendation).
    • Potassium: 2.6–3.4 g/day.
  • Typical Intake:
    • Western diets: 70–100 g/day protein, 5–10 mg/day zinc, 3–4 g/day sodium.
    • Vegetarian diets: 50–80 g/day protein, 3–8 mg/day zinc, 2–3 g/day sodium.
  • General Guidelines:
    • Consume protein-rich foods (e.g., 3 oz chicken, 1 cup lentils) for 50–70 g/day protein.
    • Include zinc (oysters, seeds) and B6 (bananas, chickpeas) daily.
    • Follow a low-sodium, high-potassium diet (e.g., fruits, vegetables) to balance RAAS.
  • Context Matters: Whole foods (e.g., salmon, quinoa) provide nutrients with synergy; limit processed high-sodium foods.

Supplementation

  • Forms:
    • Protein powders (whey, plant-based: 20–30 g protein/serving).
    • Multivitamins (2–5 mg zinc, 1–2 mg B6).
    • Electrolyte supplements (sodium, potassium: 0.5–1 g/serving).
  • Typical Doses:
    • General health: Dietary nutrients suffice (50–70 g/day protein, 8–11 mg/day zinc).
    • Recovery/Illness: 1.2–2 g/kg/day protein (e.g., kidney disease, under supervision).
    • Electrolyte balance: Sodium/potassium as needed (monitor BP).
  • Usage Notes:
    • Choose high-quality, third-party-tested supplements.
    • Take protein with meals for absorption; zinc/B6 with food to reduce GI upset.
    • Consult a healthcare provider for hypertension, heart failure, kidney disease, or RAAS-modulating drugs.

Safety, Interactions, and Side Effects

Safety Profile

  • Normal Levels: Safe at physiological concentrations (angiotensin II ~10–50 pg/mL in plasma).
  • High Levels: Chronic RAAS overactivity causes cardiovascular/renal damage; manage with lifestyle/drugs.
  • Low Levels: May lead to hypotension; adjust diet or medications.

Possible Interactions

  • Medications:
    • ACE Inhibitors/ARBs: Lower angiotensin II, reducing BP (monitor for hypotension, hyperkalemia).
    • Diuretics: Increase RAAS activity (monitor electrolytes).
    • NSAIDs: Reduce RAAS efficacy, risking kidney issues (use cautiously).
  • Nutrients:
    • Complements zinc/B6 for synthesis, potassium for RAAS modulation.
    • Low sodium (1.5–2.3 g/day) reduces RAAS activity.
  • Medical Conditions:
    • Monitor in hypertension, heart failure, kidney disease, or adrenal disorders.
    • Tailored nutrition for RAAS dysregulation.

Contraindications

  • Limit high-sodium intake (>2.3 g/day) in:
    • Hypertension, heart failure, or kidney disease (follow DASH diet).
    • Allergies to protein-rich foods (e.g., eggs, soy).
  • High protein (>2 g/kg/day) in:
    • Advanced kidney disease (consult doctor).

Fun Fact

Did you know angiotensin is like a thermostat for your blood pressure? It tightens blood vessels and dials up thirst to keep your body balanced, all thanks to the protein in your fish or beans!

Empowering Your Health Choices

Angiotensin, a key peptide hormone, regulates blood pressure, fluid balance, and cardiovascular health via the RAAS. Support its synthesis with a balanced diet providing 50–70 g/day protein from fish, eggs, or lentils, 8–11 mg/day zinc from oysters or seeds, and a low-sodium (1.5–2.3 g/day), high-potassium (2.6–3.4 g/day) diet from fruits and vegetables. For RAAS-related conditions, follow the DASH diet and consult a healthcare provider for medications like ACE inhibitors. Exercise moderately (150 min/week) and monitor for hypertension, heart failure, or kidney issues. Nourish wisely to balance angiotensin for a vibrant, healthy you!