Prostaglandins and Divalent Cation Metabolism

Abstract

When von Euler (1) first described the prostaglandins thirty years ago, he could not have imagined that these lipids would be implicated in so many physiologic roles. With the rediscovery of these lipids and the elucidation of their chemical structure by Bergstrom and Samuelsson (2), a considerable volume of information has been generated. The prostaglandins are a group of 20-carbon acidic lipids generally resembling prostanoic acid. They are derived from the enzymatic conversion of either linolenic acid (the 1-series) or arachidonic acid (the 2-series) (3,4). During their synthesis, numerous short-lived cyclic endoperoxide intermediates are formed which by themselves are frequently more active than the prostaglandins (5). Almost every cell in the body has the capacity to synthesize prostaglandins although in the adult, the major organs of synthesis are the renal medulla, seminal vesicles, and uterus. The prostaglandins that are synthesized in the microsomes are probably not stored by the cell (6), but released into the cytoplasm and eventually into the extracellular fluid. The lung, liver, and renal cortex among other tissues, have the enzymatic ability to degrade prostaglandins (7). Although dozens of prostaglandins, intermediates, and metabolites have been identified, prostaglandin-E₂ (PGE₂) and prostaglandin-F_2∝ (PGF_2∝) appear to be implicated as the active naturally occurring agents. The prostaglandins can be identified and measured by various techniques with considerable variation in sensitivity and specificity (8). These methods include gas chromatography and mass spectrometry, thin layer chromatography, radioimmunoassay, membrane receptor assay, and bioassay.