Cardiomyocytes - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 236

−

ACE2

− −

ATn2 ANP ET1

(cGMP)

−

ATn(1−7)

ERK

(cAMP)

−

Fig. 5.10 Feedback loops between atrial natriuretic peptide (ANP), angiotensin-2 (ATn2), and
endothelin-1 (ET1). Angiotensin-2 is converted to angiotensin 1 − 7 by angiotensin-converting
enzyme-2 (ACE2). Angiotensin-2 precludes ACE2 activity, thereby avoiding its conversion.
Whereas angiotensin-2 and endothelin-1 stimulate extracellular signal-related kinases ERK1 and
ERK2, atrial natriuretic peptide and angiotensin 1 − 7 inhibit ERK1 and ERK2 via cGMP and cAMP,
respectively.

proANP 31 −− 67 ;and(3) kaliuretic peptide , i.e., proANP 79 −− 98 . Peptides ANP,
vessel dilator, and long-acting natriuretic peptide bind to their specific receptors.
Cardiac hormone ANP is secreted from myoendocrine cells of atria in response to
acute or chronic stretch of the atrial myocardium. It causes diuresis, natriuresis, and
vasodilation. Atrial natriuretic peptides is indeed an endocrine regulator of blood
volume, as it increases excretion of water and sodium and potassium ions by the
renal distal convoluted tubule (Vol. 6 - Chap. 4. Cardiovascular Physiology).
In addition, circulating ANP also decreases blood pressure by impeding the
secretion of renin by the kidney and aldosterone by the zona glomerulosa of
the adrenal cortex. Furthermore, it prevents action of vasopressin as well as
vasoconstriction mediated by angiotensin-2 [ 402 ].
It operates via cGMP messenger that remove salts and water in the collecting
ducts. In addition, cGMP antagonizes the renin-angiotensin-aldosterone axis.
Messenger cGMP is also a vasodilator that increases the permeability of blood
vessels.
The antihypervolemic and antihypertensive factor ANP provokes vasodilation as
well as a concomitant leakage of fluid from blood vessels to the interstitium by
increasing the endothelial permeability to plasma proteins such as albumin [ 401 ].
Once the glycocalyx crossed, plasma proteins and solutes are transported across
the endothelium either via the transcellular route, i.e., via caveola-mediated vesic-
ular transport, or via the paracellular path, i.e., via interendothelial junctions
(Sect. 9.6 ). Hormone ANP primarily stimulates vascular permeability in the skin