Smooth Myocytes - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 437

Table 8.24. Eicosanoids associated with blood circulation (taken from [ 813 ], with permission).
( Part 1 ) Prostaglandins and prostacyclins (L : lymphocyte; TC: thrombocyte [platelet]; WBC:

white blood cell [leukocyte]; Bdk: bradykinin; His: histamine; IL: interleukin). Prostaglandin-
H2 (PGh2) is a precursor of 5 types of prostanoids using specific prostanoid synthases (PGdS,
PGeS, PGfS, and PGiS) that connect to their specific binding sites in PGh2 molecule. The
number (2) refers to the number of carbon-carbon double bonds. Synthesis of prostanoids
prostaglandins, which are mediators of inflammatory and anaphylactic reactions, thromboxanes,
which are vasoconstrictors, and prostacyclins, which operate in the resolution of inflammation,
involves a sequence of 3 stages: (1) release of arachidonic acid from phospholipids by secretory
and/or cytoplasmic phospholipase A2 (sPLA2 and cPLA2); (2) oxygenation of arachidonic acid
by cyclooxygenases to form PGh2; and (3) conversion of PGh2 to prostaglandin-D2 (PGd2),
prostaglandin-E2 (PGe2), prostaglandin-F2

ϕ

), prostacyclin (PGi2), and thromboxane-
A2 (TxA2) via 7 specific synthases, including thromboxane synthase (TxAS). Two PGdS
subtypes comprise hematopoietic (hPGdS) and lipocalin (lPGdS) synthases. Three isoforms of
PGE synthase (PGeS) encompass microsomal mPGeS1 and mPGeS2 and cytoplasmic cPGeS
enzymes.

α (PGf2 α

Type Synthesis site Activity

PGd2 Mastocyte Vasodilation

Inhibition of TC and WBC aggregation
Reduction in T-cell proliferation
Decrease in L migration

Secretion of IL1a/2

ϕ

↓

PGe2 Heart, Vasodilation

kidney, spleen TC aggregation

Reduction in T-cell proliferation
Decrease in L migration

Secretion of IL1a/2

ϕ

↓
Enhancement of Bdk and His effects

PGf2 α Heart, Vasoconstriction,

kidney, spleen bronchoconstriction

PGh2 Widespread precursor Vasoconstriction

TC aggregation

PGi2 EC Vasodilation

Inhibition of TC and WBC aggregation
Reduction in T-cell proliferation
Decrease in L migration

Reduced secretion of IL1a and IL2

ϕ

Reactive Oxygen Species

The pulmonary circulation is very sensitive to changes in the blood partial pres-
sure of oxygen. Pulmonary vessels contract in response to low oxygen content
in blood, whereas systemic vessels dilate [ 816 ]. Reversible vasoconstriction of
pulmonary artery smooth myocytes is a compensatory response that redirects blood
to better ventilated lung regions. Pulmonary vessel constriction also results from an