Systemic control by hormone

[Ref: WG21:chp31]

Vasodilator hormones

• Kinins
• VIP
• ANP
• Substance P

Vasoconstrictor hormone

• Vasopression (ADH)
• Norepinephrine
• Epinephrine
• Angiotensin II
• Neuropeptide Y

Kinins

Two types:

1. Bradykinin
2. Lysylbradykinin (or kallidin)

Both are inactivated by kininase I or kininase II
--> Kininase II = Angiotensin-converting enzyme

Production of kinins

Two types of precursors

1. High-molecular-weight kininogen
2. Low-molecular-weight kininogen

Kallikreins (proteases) release (activate) the two types of kinins

2 types of kallikreins:

1. Tissue kallikreins
   * Produce lysylbradykinins from HMWK and LMWK
2. Plasma kallikrein
   * Normally circulate in inactive form (prekallikrein)
   * Produces bradykinin from HMWK

Positive feedback with factor XII

• Prekallikrein is converted to active form (kallikrein) by active factor XII.
• Kallikrein also activate factor XII

--> Positive feedback.

HMWK also has some effect in activating factor XII

Actions of kinins

Similar to histamine

• Contraction of visceral smooth muscle
• Relaxation of vascular smooth muscle (via NO)
  --> Lower BP
• Increase capillary permeability
• Attract leukocytes
• Cause pain upon injection into skin

 

Natriuretic hormones

Antagonise the action of various vasoconstrictor agents and lowers BP

Exact role in regulation
--> unsettled [WB21:p604]

Vasopressin (ADH)

Potent vasoconstrictor

When injected in normal person
--> Compensatory decrease in cardiac output
--> BP unchanged

 

Catecholamines

Norepinephrine

• Generalised vasoconstrictor

Epinephrine

• Dilates vessels in skeletal muscles and liver

 

Angiotensin II

• Generalised vasoconstrictor
• Also increase thirst and aldosterone secretion