PGE2 reduces net water and chloride absorption from the rat colon by targeting the Na+/H+ exchanger and the Na+ K+ 2Cl- cotransporter

Mechanism of Na-K-ATPase Inhibition by PGE2 in Intestinal Epithelial Cells

The primary means of intestinal absorption of nutrients by villus cells is via Na-dependent nutrient co-transporters located in the brush border membrane (BBM). These secondary active co-transport processes require a favorable transcellular Na gradient that is provided by Na-K-ATPase. In chronic enteritis, malabsorption of essential nutrients is partially due to inhibition of villus Na-K-ATPase activity mediated by specific immune inflammatory mediators that are known to be elevated in the inflamed mucosa. However, how Prostaglandin E2 (PGE2), a specific mediator of nutrient malabsorption in the villus BBM, may mediate the inhibition of Na-K-ATPase is not known. Therefore, this study aimed to determine the effect of PGE2 on Na-K-ATPase in villus cells and define its mechanism of action. In vitro, in IEC-18 cells, PGE2 treatment significantly reduced Na-K-ATPase activity, accompanied by a significant increase in the intracellular levels of cyclic Adenosine Monophosphate (cAMP). The treatment with cAMP analog 8-Bromo-cAMP mimicked the PGE2-mediated effect on Na-K-ATPase activity, while Rp-cAMP (PKA inhibitor) pretreatment reversed the same. The mechanism of inhibition of PGE2 was secondary to a transcriptional reduction in the Na-K-ATPase α1 and β1 subunit genes, which was reversed by the Rp-cAMP pretreatment. Thus, the PGE2-mediated activation of the PKA pathway mediates the transcriptional inhibition of Na-K-ATPase activity in vitro.

Dietary fish oil reduces glomerular injury and elevated renal hydroxyeicosatetraenoic acid levels in the JCR:LA-cp rat, a model of the metabolic syndrome

We have previously shown nutritional intervention with fish oil (n-3 PUFA) to reduce numerous complications associated with the metabolic syndrome (MetS) in the JCR:LA-corpulent (cp) rat. In the present study, we sought to explore the potential role of fish oil to prevent glomerulosclerosis in JCR:LA-cp rats via renal eicosanoid metabolism and lipidomic analysis. Male lean and MetS JCR:LA-cp rats were fed a lipid-balanced diet supplemented with fish oil (5 or 10 % of total fat). After 16 weeks of feeding, albuminuria was significantly reduced in MetS rats supplemented with 5 or 10 % fish oil ( − 53 and − 70 %, respectively, compared with the untreated MetS rats). The 5 % fish oil diet resulted in markedly lower glomerulosclerosis ( − 43 %) in MetS rats and to a lesser extent in those supplemented with 10 % fish oil. Interestingly, untreated MetS rats had higher levels of 11- and 12-hydroxyeicosatetraenoic acids (HETE) v. lean rats. Dietary fish oil reduced these levels, as well as other (5-, 9- and 15-) HETE. Whilst genotype did not alter prostanoid levels, fish oil reduced endogenous renal levels of 6-keto PGF1α (PGI2 metabolite), thromboxane B2 (TxB2), PGF2α and PGD2 by approximately 60 % in rats fed 10 % fish oil, and TxB2 ( − 50 %) and PGF2α ( − 41 %) in rats fed 5 % fish oil. In conclusion, dietary fish oil prevented glomerular damage in MetS rats and mitigated the elevation in renal HETE levels. These results suggest a potential role for dietary fish oil to improve dysfunctional renal eicosanoid metabolism associated with kidney damage during conditions of the MetS.

Stress and expression of cyclooxygenases (cox1, cox2a, cox2b) and intestinal eicosanoids, in Atlantic salmon, Salmo salar L

Prostaglandin H synthetases (cyclooxygenases) catalyze the initial reactions leading to prostanoids in animals. They form interesting links between diet and fish physiology as the type and nature of eicosanoids are affected by dietary lipid sources. Their expression is likely to be affected by tissues and environmental conditions leading to altered amount and ratio of eicosanoids. These mechanisms are, however, poorly understood in fish. In the present study, Atlantic salmon Salmo salar L. (1,000 g, 10°C, seawater) were subjected to acute chasing stress. Liver, kidney, spleen, gill, muscle, midgut and hindgut were extracted before and 1 h post-stress and analyzed for mRNA expression of cox1, cox2a and cox2b. Intestinal samples were further sampled over 24 h for both cox expression and analysis of 15 eicosanoids and isoprostanes of the n-3 and n-6 series. Results show a highly variable but consecutively expression of cox1, cox2a and cox2b in most of the tissues analyzed. Low levels were only found for cox2a in liver and cox2b in liver and kidney. The study reveals the general trend that cox1 is about 10 times the level of cox2b, which again is about 10 times the level of cox2a. Cox2b shows the highest level of expression in the gills indicating a possible higher requirement for this protein in gills. Imposing stress to the fish induces a temporal increase in the expression of cox2a in the midgut, while the gene expression of the other genes is not affected in any of the tissues analyzed. There is, however, a general tendency to increased expression of both cox2 genes that merits further studies. Stress had a profound effect on the intestinal eicosanoid content which showed a general decrease in midgut sections after stress that persisted for at least 24 h.