Formation of 8-iso-PGF(2alpha) and thromboxane A(2) by stimulation with several activators of phospholipase A(2) in the isolated human umbilical vein

Abstract

We investigated the effects of the phospholipase A(2) (PLA(2)) activators calcium ionophore A 23187, hydrogen peroxide (H(2)O(2)), bradykinin (BK), histamine and noradrenaline (NA) on the 8-iso-prostaglandin (PG)F(2alpha) formation in the isolated human umbilical vein and the isolated rabbit ear. For comparison, the influence of these substances on the thromboxane A(2) (TXA(2)) release was also investigated. The release of total (esterified as well as free) 8-iso-PGF(2alpha), free 8-iso-PGF(2alpha) and TXB(2), the stable metabolite of TXA(2), was determined by specific enzyme immunoassays. The results show that bolus injections of 5.4 mmol H(2)O(2), 30 nmol A 23187, 10 nmol BK, 50 nmol histamine and 20 nmol NA caused an increased release of total 8-iso-PGF(2alpha) in the umbilical vein and the rabbit ear. A perfusion with H(2)O(2) at a final concentration of 0.3 mM also increased the release of this isoprostane. Increased formation of free 8-iso-PGF(2alpha) was induced by A 23187 injection and by both modes of H(2)O(2) administration, but not by the other treatments. Bolus injections of A 23187, BK and histamine induced an increased release of TXB(2) in both organs. Both modes of H(2)O(2) administration and NA showed no releasing effects. In conclusion, our results show that the substances used are able to stimulate the formation of 8-iso-PGF(2alpha) concurrently with the release of PGs. This effect might be of pathophysiological relevance in inflammatory and cardiovascular diseases in which an enhanced release of free radicals, BK, histamine or NA play an important role.

Figure 1

Release of total (left graph) and free (right graph) 8-iso-PGF_2α in pg sample⁻¹ (6 ml) induced by bolus injections of 30 nmol A 23187 in the isolated human umbilical vein (A) and the isolated rabbit ear (B). Vertical bars represent s.e.mean. Significance of difference from controls: ^*P<0.05, ^**P<0.01. n=4.

Figure 2

Release of total (left graph) and free (right graph) 8-iso-PGF_2α in pg sample⁻¹ (6 ml) induced by bolus injections of 50 nmol histamine in the isolated human umbilical vein (A) and the isolated rabbit ear (B). Vertical bars represent s.e.mean. Significance of difference from controls: ^**P<0.01. n=4.

Figure 3

Release of total (left graph) and free (right graph) 8-iso-PGF_2α in pg sample⁻¹ (6 ml) induced by bolus injections of 5.4 mmol H₂O₂ in the isolated human umbilical vein (A) and the isolated rabbit ear (B). Vertical bars represent s.e.mean. Significance of difference from controls: ^*P<0.05, ^**P<0.01. n=4.

Figure 4

Release of total 8-iso-PGF_2α in pg sample⁻¹ (6 ml) induced by bolus injections of 10 nmol bradykinin (A) and 20 nmol noradrenaline (B) in the isolated human umbilical vein (left graph) and the isolated rabbit ear (right graph). Vertical bars represent s.e.mean. Significance of difference from controls: ^*P<0.05, ^**P<0.01. n=4.

Figure 5

Release of total (left graph) and free (right graph) 8-iso-PGF_2α in pg sample⁻¹ (6 ml) induced by perfusions with 0.3 mM H₂O₂ in the isolated human umbilical vein (A) and the isolated rabbit ear (B). Vertical bars represent s.e.mean. Significance of difference from controls: ^*P<0.05, ^**P<0.01. n=4.

Figure 6

Release of total TXB₂ in pg sample⁻¹ (6 ml) induced by bolus injections of 30 nmol A 23187 (A) and 5.4 mmol H₂O₂ (B) in the isolated human umbilical vein (left graph) and the isolated rabbit ear (right graph). Vertical bars represent s.e.mean. Significance of difference from controls: ^*P<0.05, ^**P<0.01.

Figure 7

Release of total TXB₂ in pg sample⁻¹ (6 ml) induced by bolus injections of 50 nmol histamine (A) and 10 nmol bradykinin (B) in the isolated human umbilical vein (left graph) and the isolated rabbit ear (right graph). Vertical bars represent s.e.mean. Significance of difference from controls: ^*P<0.05, ^**P<0.01.