Smooth Myocytes - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 432

Table 8.18. Vasomotor tone-regulating substances (ANP: atrial natriuretic peptide; DHET:
dihydroxyeicosatrienoic acid; EDHF: endothelial-derived hyperpolarizing factor; EET: epoxye-
icosatrienoic acid; ET: endothelin; H 2 S: hydrogen sulfide; HEET: hydroxyepoxyeicosatrienoic;
NO: nitric oxide; NPY: neuropeptide-Y; PGf2: prostaglandin-F2; PGi2: prostacyclin; S1P: sphin-
gosine 1-phosphate; THET: trihydroxyeicosatrienoic acid; TxA2: thromboxane-A2; UP 4 A: uridine
adenosine tetraphosphate; 5HT: serotonin). These chemical messengers function in blood vessels
as directly or indirectly acting vasoconstrictors or vasodilators. Numerous vasoactive substances
are synthesized by endothelial cells.

Vasoconstrictor Vasodilator

ET1 NO

TxA2 H 2 S

PGf2 α PGi2

UP 4 A EDHF (EET, DHET, HEET, THET)

ATP Acetylcholine

5HT ANP

NPY Adrenomedullin

20HETE Urocortin

Apelin Ghrelin

Motilin Nociceptin

Neuromedin-U
S1P
Urotensin-2

cascades; and (3) transcription regulation [ 810 ]. Several endothelial genes are
regulated by mechanical stress [ 811 ]. Transcriptional response to wall shear stress
target only certain promoters.

8.5.8.4 Vasoactive Substances

Several substances, once bound to specific surface receptor, locally cause either
SMC contraction or relaxation (Table 8.18 ). Among these substances, some are
released by neighboring endothelial cells, thereby acting as indirect vasoconstrictors
or vasodilators. In human arteries, in addition to the action of the sympathetic ner-
vous system, these locally produced mediators regulate the vasomotor tone. Nitric
oxide and endothelin-1 are the major endothelial-derived opposing vasodilator and
vasoconstrictor, respectively.

G-Protein-Coupled Receptors and Vasomotor Tone

Among vasomotor regulators that bind to G-protein-coupled receptors (Vol. 3 -
Chap. 7. G-Protein-Coupled Receptors), some GPCRs mediate vasoconstriction
(Tables 8.19 to 8.21 ), whereas others prime directly or indirectly vasodilation
(Table 8.22 and 8.23 ). The expression of receptors varies among distinct vascular