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:
- Bradykinin
- Lysylbradykinin (or kallidin)
Both are inactivated by kininase I or kininase II
--> Kininase II = Angiotensin-converting enzyme
Production of kinins
Two types of precursors
- High-molecular-weight kininogen
- Low-molecular-weight kininogen
Kallikreins (proteases) release (activate) the two types of kinins
2 types of kallikreins:
- Tissue kallikreins
* Produce lysylbradykinins from HMWK and LMWK
- 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
