VPT 321: Veterinary Neuropharmacology (2+1)

Actions of angiotensin

PHARMACOLOGICAL ACTIONS OF ANGIOTENSN II

CVS

• Prominent action is vasoconstriction through adrenaline or nor adrenaline or by increasing sympathetic outflow.
• Vasoconstriction is involved in all vascular beds with less marked constriction effects on cerebral, skeletal muscle, pulmonary and coronary vessels.
• It is more potent than nor adrenaline which promotes fluid movement from vascular to extravsacular compartment and cause rise of blood pressure
• Continuous perfusion cause a sustained rise of blood pressure and reabsorption of salt and water.
• Promote calcium ion influx and increase myocardial contraction.
• Increases heart rate by enhancing sympathetic outflow, cardiac output is reduced and cardiac work is increased.
• Contributes to the hypertrophy and remodelling of heart and blood vessels. ACE inhibitor retards/reverses many of these changes imparted by AII.

Smooth muscles

• On many visceral smooth muscles invivo actions are insignificant.

Adrenal cortex

• Angiotensin II and III are trophic in action enhances synthesis and release of aldosterone. Acts on distal tubules, promotes reabsorption of sodium ions and excretion of potassium and hydrogen excretion

Kidney

• Exerts indirect effect through aldosterone.
• Promotes sodium and potassium ion exchange in proximal tubule leading to increased sodium, chloride and bicarbonate ion reabsorption.
• Reduces renal blood flow resulting in sodium and water retention and increases potassium excretion.

CNS

• On systemic administration enter periventricular areas of the brain and induce drinking behaviour and anti diuretic hormone release.
• Increases sympathetic outflow and contributes to pressor effects.
• Peripheral sympathetic structures act in response to adrenaline release from adrenal medulla and stimulation of autonomic ganglia.