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angiotensin II

(Patho)physiology: the body has 3 control systems to regulate arterial blood pressure (1):
  • "Immediate control": the autonomic nervous system reflexes are capable of minute-to-minute control of blood pressure (1).
  • "Intermediate control": renin and angiotensin (1).
  • "long-term control": occurs hours after the decrease in blood pressure by altering the sodium and water balance. This process is mediated by aldosterone with the aim of restoring blood pressure to a normal level (1).
Angiotensin II ist an octapeptide. Not all of it comes from conversion of angiotensin I by angiotensin converting enzyme; it is also generated by the vascular endothelium (64%); plasma half-life is about 50 seconds and it is cleared rapidly by a variety of enzymes, namely angiotensinases, in the circulation (1).

Symptoms:
  • Cardiovascular system: it binds to angiotensin AT 1 receptor on the vascular smooth muscle, leading to vasoconstriction of the precapillary arterioles and postcapillary venules. It is 40x more potent than norepinephrine, which makes it the most powerful endogenous vasoconstrictor. This effect is most profound in the skin, splanchnic vasculature, and kidneys, and can lead to significant decreases in blood flow to these organs. These pressor responses do not lead to a reflex bradycardia since angiotensin II acts centrally to reset the baroreceptor reflex to a higher pressure (1).
  • Central venous system: it acts on the medullary vasomotor center leading to sustained hypertension. It can also enhance the release of vasopressin and adrenocorticotropic hormone (ACTH) as well as regulate prolactin release in the pituitary gland (1).
  • Peripheral autonomic nervous system: it can stimulate the chromaffin cells in the adrenal medulla to release catecholamines, which is the underlying mechanism for marked hypertension associated with pheochromocytoma (1).
  • Adrenal cortex: it can stimulate the synthesis and secretion of aldosterone from the adrenal cortex, leading to retention of sodium and excretion of potassium and hydrogen in the kidneys (1).
  • Urogenital: it regulates ovulation and hormone production in the ovary and hormone production in the testes. It may be partially responsible for preeclamptic symptoms (1).
References:
  1. Angiotensin. 5-Minute Anesthesiology Consult: full text.