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heart, lung, kidney, and stomach, although its expression in these tissues
does not vary during the estrous cycle as does in the corpus luteum (44).
There are several splice variants of FP (FPA and FPB) but its particular
role is unclear.

IP is expressed in larger quantities by dorsal root ganglion neurons
but also by platelet precursors (megakaryocytes) as well as in the smooth
muscle cells of arteries consistent with the important action of PGI2 in the
cardiovascular system (45).

PGE2 has four receptors, EP1 to 4. In addition, there are several
splice variants of EP3. More importantly, each one is linked to a different
transduction pathway that may even give rise to opposite effects
(activation or inhibition) on cellular responses (6). Thus, EP1 induces an
inhibition of adenylate cyclase leading to a decrease in cAMP whereas
EP2 and EP4 receptors activate this enzyme. On the other hand, EP3 is

coupled to Gaq and its activation results in intracellular calcium increase.
EP3 and EP4 receptors have a wide distribution throughout the body,
being expressed in almost all tissues examined. In contrast, of EP1 is
restricted to the lung, kidney and stomach, and EP2 is scarcely expressed.

In the cardiovascular system, IP, DP, EP4 and EP2 receptors that
mediate cAMP increases are termed “relaxant” receptors, whereas TP,
FP, and EP1 receptors, which induce calcium mobilization, represent the
“contractile” receptor group. EP3, which reduces cAMP levels, has been
named the “inhibitory” receptor (6).

Nuclear actions of prostanoids have also been reported. Thus,
PGJ2 derivatives can bind and activate peroxisome proliferator-activated
receptors (PPARs) nuclear transcription factors (46). There are four types
of PPARs (alpha, delta, gamma-1, and gamma-2), which may bind
various PGs with different sensitivity (47). In this way, PGs may also act
as intracellular signalling molecules and regulate gene expression (48).
Generally PPARs induces transcription of anti-inflammatory genes as
well as inhibits activation of pro-inflammatory ones (46). Besides,
cyclopentenone PGs (that includes PGA1) have a reactive ring which may
lead to have receptor-independent actions through redox alterations (49).

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