Prostaglandins (PGs) are often mentioned in the context of mammalian physiology and pathophysiology. It is now known that PGs are present and play important roles in almost all mammalian tissues and fluids (Horrobin 1978). The term eicosanoids was introduced by Corey et al. (1980) to encompass various biologically active derivatives of eicosapolyenoic acids, especially arachidonic acid. The eicosanoid family includes PGs, thromboxanes (TXs), hydroperoxy- and hydroxyeicosatetraenoic acids (HPETEs and HETEs), the leukotrienes (LTs), and lipoxins (LXs). The term eicosanoids has not been used uniformally in this review. Terms like prostaglandins, thromboxanes, etc. have been preferred, and they appear at appropriate places in keeping with the tradition followed by various researchers who have contributed to the development of this area of research in biology and medicine. Although interest in the biological significance of these compounds was essentially based on the physiological studies in mammals traceable to the early part of this century, the PGs were not studied from non-mammalian organisms until the first report appeared of PGs in an invertebrate animal, the gorgonian coral Plexaura homomalla (Weinheimer and Spraggins 1969). Since then, occurrence of PGs in over 100 invertebrate species, several fish, and amphibian species has been reported.

Prostaglandins (Eicosanoids) and Their Role in Ectothermic Organisms

Effect of prostaglandins on renal salt and water excretion.

Biochemistry and pharmacology of renal arachidonic acid metabolism

An extracellular adenosine responsive site that stimulates adenylate cyclase activity has been identified in several tissues. There is limited information on the presence and physiologic significance of adenosine receptors in well-defined segments of the mammalian nephron. We therefore examined the effect of adenosine and selected analogues on basal hydraulic conductivity in rabbit cortical collecting tubules (CCT) perfused in vitro. Adenosine and analogues with an intact ribose moiety produced a significant, sustained increase in hydraulic conductivity. No increase in hydraulic conductivity was seen in either time control CCT's or CCT's exposed to an adenosine analogue with an altered ribose moiety. These experiments are compatible with the presence of a functional adenosine receptor which requires an intact ribose moiety and acts to increase hydraulic conductivity in the mammalian CCT.

Purinergic regulation of basal and arginine vasopressin-stimulated hydraulic conductivity in rabbit cortical collecting tubule.

4 – Other Essential Fatty Acids, Their Metabolites and Cell–Cell Interactions

The effects of prostaglandins of the E series on sodium and water transport have been studied extensively. PGE2 has been shown to inhibit the increase in osmotic water flow produced by vasopressin and to stimulate short-circuit current (SCC) in the toad bladder. On the other hand, the effects of prostacyclin (PGI2), an arachidonic acid product, on sodium and water transport have not been extensively evaluated. The present studies describe the effects of PGI2 on basal and vasopressin-stimulated osmotic water flow and on SCC in the urinary bladder of the toad. Studies were performed in the absence or presence of indomethacin. PGI2 in the absence of indomethacin had no effect on basal or vasopressin-stimulated osmotic water flow. When indomethacin was present, thereby eliminating intrinsic prostaglandin biosynthesis, PGI2 inhibited basal but not vasopressin-stimulated osmotic water flow. PGI2 increased SCC in the presence or absence of indomethacin. 6-keto PGF1 alpha, the stable metabolite of PGI2, had no effect on SCC. PGI2 stimulated cAMP production in isolated toad bladder epithelial cells. 2',5'-Dideoxyadenosine, an inhibitor of cAMP production, blocked the increase in SCC produced by PGI2, suggesting that the effects of this compound on SCC are mediated via cAMP.

P. Needleman

Papers

Effects of prostacyclin on short-circuit current and water flow in the toad urinary bladder.