6KPGF1 Alpha Research Articles

Interaction between lymphocytes and platelets in the synthesis of prostacyclin.

To test the hypothesis that prostacyclin (PGI2) is formed via a biochemical interaction between platelets and lymphocytes, we measured eicosanoids by high performance liquid chromatography (HPLC) and radioimmunoassay (RIA). A distinct 6-keto-prostaglandin F1 alpha (6KPGF1 alpha) peak was noted when [14C]arachidonic acid ([14C]AA) was added to the mixed cell preparations which was increased by pretreating platelets with 1-benzylimidazole (1-BI). Lymphocytes prelabeled with [14C]AA failed to form 6KPGF1 alpha when stimulated with phytohemagglutinin (PHA) or ionophore A23187. When the prelabeled platelets were suspended together with aspirin-treated lymphocytes and stimulated with ionophore, thrombin, or collagen, a 6KPGF1 alpha peak was detected and enhanced by 1-BI. These results were supported by quantifying the 6KPGF1 alpha content in the HPLC-purified fraction by RIA. Adding prostaglandin H2 (PGH2) directly to lymphocytes led to 6KPGF1 alpha production. Platelet aggregation and release were inhibited by lymphocytes in a dose-related manner. We conclude that lymphocytes possess PGI2 synthase activity which is capable of converting platelet-derived PGH2 into PGI2. PGI2 formed is sufficient to inhibit platelet function.

Endotoxin protection against pulmonary oxygen toxicity and plasma prostaglandin levels in the rat.

Exposure of rats to high concentrations of oxygen (greater than 95%) at 1 ATA pressure (101 kPa) is lethal within three days. Rats treated with a small dose of endotoxin are protected against these lethal effects of hyperoxia. Recently, we found that the lysine salt of acetylsalicylic acid antagonises this protective action of endotoxin. This suggests that prostaglandin metabolism plays an important role in the protective action of endotoxin against pulmonary oxygen toxicity. Therefore, we measured the plasma levels of 6KPGF1 alpha, a stable degradation product of prostacyclin (PGI2), PGE2 and thromboxane B2, the stable degradation product of thromboxane A2, in rats exposed to air or greater than 95% oxygen for 48 hours. We compared these with the plasma levels of rats treated with endotoxin (Salmonella typhimurium lipopolysaccharide 1 mg/kg) and exposed to air or greater than 95% oxygen for 48 hours. We found that exposure of rats to greater than 95% oxygen for 48 hours leads to a significant rise in the 6KPGF1 alpha levels. Rats exposed to greater than 95% oxygen for 48 hours and treated with endotoxin had significantly higher PGE2 and significantly lower 6KPGF1 alpha plasma levels than saline-treated rats exposed to greater than 95% oxygen for 48 hours.

Is thromboxane a potent antinatriuretic factor and is it involved in the development of acute renal failure?

Glycerol-treated rats exhibited significantly increased urinary thromboxane B2(TXB)2, prostaglandin E2 (PGE2) and 6-ketoprostaglandin F1 alpha (6kPGF1 alpha) excretion and urine volume (UV). These increases were associated with significant decreases in creatinine clearance (CCr), urinary sodium concentration (UNa), urinary sodium excretion (UNaV), and fractional excretion of sodium (FENa%), which is consistent with the development of the prerenal (reversible) phase of acute renal failure (ARF). When glycerol-treated rats were pretreated with a selective inhibitor of thromboxane A2 (TXA2) synthesis (imidazole), urinary PGE2 and 6kPGF1 alpha excretion and UV remained unchanged, whereas CCr, UNa, UNaV decreases were partially prevented. Additionally, FENa% was increased, indicating inhibition of sodium reabsorption. The findings indicate that inhibition of TXA2 synthesis increases UNaV and partially improves CCr in glycerol-treated rats. Further histologic observation and functional follow-up over longer periods of time are needed to clarify the role of TXA2 in the development of ARF.

Intrarenal prostaglandin release: Effects of arachidonic acid and hyperchloremia

We measured the release of PGE2, 6kPGF1 alpha, PGF2 alpha, and TXB2 into urine (U) and renal hilar lymph (L) to assess the possible roles of intrarenal prostaglandins (PGs) in arachidonic acid (AA)-induced renal vasodilation and Cl-induced renal vasoconstriction, (a model of tubuloglomerular feedback, TG). AA caused an ipsilateral fall in renal vascular resistance (RVR) and diuresis and increased release of all PGs into U; release of 6kPGF1 alpha into L increased ninefold. Hypertonic NaCl infusion caused ipsilateral vasoconstriction and decreased GFR; the release of TXB2 into U and L increased, but other PGs were not altered consistently. During a background infusion of AA, hypertonic NaCl infusion again evoked TXB2 release into U and L without significant changes in other PGs. AA attenuated the NaCl-induced renal vasoconstriction in dogs with the highest rates of PGE2 release into L. Changes in RVR correlated with the ratio of excretion of vasodilator PG (PGE2 + 6kPGF1 alpha) to TXB2 (r = -0.74). Indomethacin administration blunted, but did not abolish, the Cl-induced increase in RVR. In conclusion, (1) AA evokes the release of PGs, especially prostacyclin, into renal cortex; (2) hypercholoremia increases RVR and evokes a rather selective release of renal TX; (3) the production of vasodilator PGs by AA may attenuate Cl-induced renal vasoconstriction; (4) renal vasodilator and vasoconstrictor PGs can be released relatively independently--their balance could modulate RVR during activation of the TG response.

Serum prostacyclin binding defects in thrombotic thrombocytopenic purpura.

To understand the pathophysiologic significance of abnormal serum prostacyclin (PGI2) binding activities in thrombotic thrombocytopenic purpura (TTP), we evaluated the PGI2 binding characteristics in three chronic TTP sera and 19 normal sera. PGI2 binding by serum was rapid and reversible. The binding activity in TTP sera (22.1 +/- SD, 4.4%) was significantly lower than that of normal sera (42.2 +/- 6.2%). Moreover, the antiaggregating activity and 6-keto-prostaglandin F1 alpha (6KPGF1 alpha) content in the gel filtrates representing the binding peak was proportionally lower in a TTP serum than normal serum. Although normal and TTP sera bound [14C]arachidonate with similar activity, and neither bound [3H]6KPGF1 alpha, there was a difference in prostaglandin E1 (PGE1) binding. Binding of [3H]PGE1 was subnormal in two TTP sera (W.J. and T.G.) and normal in the third (H.S.). Normal serum corrected the binding defects of TTP serum. Interestingly, the mixture of two TTP sera (W.J. and H.S.) mutually corrected their PGI2 binding defects. In addition, although in vivo plasma transfusions improved the PGI2 binding activity of W.J. and H.S., there existed a striking difference in the nature of their response. These observations indicate that there is at least two types of PGI2 binding defects in TTP. Our data indicate that TTP is associated with diminished serum binding of PGI2. This defect may reduce the availability of PGI2 to damaged vascular sites and decrease an important modulator of platelet thrombus formation at times of severe vascular insult.

Evidence for isosorbide dinitrate (ISDN) promoting effect on prostacyclin release by the lung and prostacyclin implication in ISDN-induced inhibition of platelet aggregation in humans

We investigated thromboxane B2 (TxB2), 6-keto-PGF1 alpha (6KPGF1 alpha reflecting prostacyclin), PGE2 and PGF2 alpha plasma levels; TxB2, PGE2 and PGF2 alpha platelet production and platelet aggregation response in ascending aorta (reflecting trans-pulmonary difference) and in venous coronary sinus (reflecting transcardiac difference) simultaneously in patients with ischemic heart disease, before and after right-atrial administration of 3 mg ISDN bolus. Transcardiac differences were scarce before as well as after ISDN administration. In aortic blood, ISDN administration into the right atria resulted in a significant increase in prostacyclin and PGF2 alpha plasma levels (472% and 242%, respectively), a decrease of both PGE2 plasma level (−173 %) and PGE2 platelet production (−485%) and a marked lowering of platelet aggregation response to ADP, concomittantly. In contrast, TxB2-related features were poorly affected by ISDN. In coronary sinus blood, the aortic increase in 6KPGF1 alpha and PGF2 alpha plasma levels was detected to a lower extent whereas the characteristics of platelet aggregation had returned to control levels. By contrast, PGE2 plasma level (−191%) and PGE2 platelet production (−133%) were lower than prior ISDN administration. The results we report here, strongly support the view that ISDN promotes release of prostacyclin and PGF2 alpha from the lung and inhibit PGE2 production. These prostanoids may be responsible for the concomittant platelet reactivity lowering, thus providing a basis for understanding how ISDN might relieve myocardial ischemia favoring prostanoid-mediated vasodilation and inhibition of platelet reactivity.