Arachidonic acid metabolism in gill homogenate and isolated gill cells from rainbow trout, Oncorhynchus mykiss: the effect of osmolality, electrolytes and prolactin

Abstract

An assay method based on thin layer chromatography to study the arachidonic acid (AA) metabolism in gill tissues was optimized and the effect of osmotically different incubation mediums on AA metabolism was evaluated. Rainbow trout gill tissues metabolize AA into PGE2 in highest concentration followed by PGD2, PGF2α and 6-keto-PGF1α (the stable metabolite of PGI2) among the prostanoids tested. Approximately 40% of PGE2 is synthesized within the first minute of incubation and is directly dependent on the substrate concentration (AA). As in mammalian tissues, PGE2 synthesis in fish gills is inhibited by the cyclooxygenase inhibitor indomethacin. PGE2 synthesis in gill homogenate and isolated gill cells incubated in trout Ringer was 0.45 and 1.9 ng/mg protein, respectively, and increased to 8.9 and 4.3 ng/mg protein, respectively, when incubated in KPO4 buffer, due to a ten-fold increase in the free AA. The hydroxy acid synthesis of the gill homogenate was higher (13%), and that of the isolated gill cells incubated in KPO4 buffer was lower (44%) compared to gill homogenate and cells incubated in trout Ringer. Gill homogenate incubated in 50 mM phosphate buffer with increasing sodium or potassium concentrations (up to 250 mM) exhibited a concentration-dependent increase in PGE2 synthesis (220% and 72%, respectively). Prolactin stimulated the PGE2 synthesis up to 30% while PGD2, PGF2α and 6-keto-PGF1α synthesis was not affected. This effect of prolactin was maximal when PGE2 synthesis was estimated 30 minutes after prolactin addition and diminished after two hours. These results suggest that rainbow trout gills possess the ability to metabolize AA through the cyclooxygenase and lipoxygenase pathways. PGE2 synthesis may be under the influence of ion balance and prolactin availability, indicating the probable involvement of AA metabolites in the regulation of ion balances across the gill membrane.

Involvement of Cytochrome P450 1A in the toxicity of aryl hydrocarbon receptor agonists : alteration arachidonic acid metabolism and production of reactive oxygen species

“…Physiological roles for cyclooxygenase-and lipooxygenase-derived AA metabolites have been demonstrated in fish (66,67). Our results and those of Oleksiak et a/.…”

The effects of arachidonic acid on the endocrine and osmoregulatory response of tilapia (Oreochromis mossambicus) acclimated to seawater and subjected to confinement stress

“…In contrast, the same dietary ArA supplementation reduced plasma cortisol levels before as well as after confinement in (SW) gilthead sea bream (Sparus aurata;Van Anholt et al, 2004b). The mechanism underlying the contrasting effects of ArA supplementation in SW compared with FW tilapia, and in tilapia compared with gilthead sea bream, needs to be elucidated, but it could be analogous to the stimulating of the release of prostaglandins in gill homogenates of rainbow trout by external salinity (Brown et al 1991;Beckman and Mustafa 1992).…”

Arachidonic acid reduces the stress response of gilthead seabream Sparus aurata L.

“…The conversion process begins when stress-related triggers induce the release of ArA within 5-60·s by activating phospholipases, mainly PLA2 (Axelrod et al, 1988;Smith, 1989;Buschbeck et al, 1999). It is often assumed that the effects of dietary ArA on fish are mainly due to its function as a precursor to these eicosanoids, particularly the prostaglandins of the 2-series (Beckman and Mustafa, 1992;Bell et al, 1995;Harel et al, 2001;Bell and Sargent, 2003). The prostaglandins are known to control a wide variety of physiological processes in mammals as well as in fish, including respiratory and cardiovascular output (McKenzie, 2001), ovulation and spawning behavior, oocyte maturation, nervous system function, osmoregulation (Mustafa and Srivastava, 1989) and immune functions (Rowley et al, 1995).…”