Molecular mechanisms of action of prostaglandin E2 in the regulation of water osmotic permeability.

The functional role and molecular mechanisms of action of prostaglandin E2 (PGE2) in the regulation of water osmotic permeability in osmoregulatory epithelia (mammalian collecting tubules and amphibian urinary bladder) are considered. The paper describes the modern classification of PGE2 receptors, their distribution along a nephron and receptor-coupled intracellular second messenger systems. The mechanism of the inhibitory action of PGE2 on the antidiuretic hormone-induced enhancement of water osmotic permeability is analyzed. Special attention is given to the role of PGE2 as an auto- or paracrine regulator of water osmotic permeability in the phenomenon of ADH-independent increase of water permeability observed in an isolated amphibian urinary bladder in replacements of the surrounding serous solution. It is concluded that the osmoregulatory epithelium is not only a place of the maximum level of PGE2 synthesis in the kidney but is also characterized by a great diversity of PGE2 receptor subtypes: EP1, EP2, EP3 and EP4 have been revealed in the mammalian collecting tubules. Such a diversity of PGE2 receptors is in a good agreement with different functional effects of PGE2 in the osmoregulatory epithelium. The data considered suggest that PGE2 is not less important in the regulation of water and ion transport in the osmoregulatory epithelium than antidiuretic hormone.