| Popis: |
Prostaglandins (PGs) are a group of compounds which have been found to exert numerous and potent physiologic and pharmacologic effects. Their existence was originally reported in seminal fluid about 50 years ago (Kurzrok and Lieb 1930; Goldblatt 1933; von Euler 1934), but the structure of the six primary PGs was only described in the early 1960s (review in Bergstrom et al. 1968). PGs are found in all mammalian tissues which also appear able to synthesize them. The precursors of PGs are essential fatty acids with varying degrees of unsaturation, mainly arachidonic acid (C20:4) and γ-dihomolinolenic acid (C20:3), originating from the plasma membrane phospholipids. In response to various stimuli, these acids are cleaved from the membrane phospholipids by the enzyme phospholipase A2 and are then acted on by a complex group of enzymes given the generic name “prostaglandin synthetase”; the first step involves a cyclooxygenase, which transforms arachidonic acid into cyclic endoperoxides (PGG2 and PGH2); these unstable intermediates, with very short half-lives, are rapidly converted into PGE2, PGF2α, thromboxane A2 (TXA2), or prostacyclin (PGI2), depending upon the tissues considered (Fig. 1, review in Samuelsson et al. 1980). |
