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The isoprostanes, 8-iso-PGF2alpha and 8-iso-PGE2, are powerful vasoconstrictors in vitro and in vivo. Increased formation of 8-iso-PGF2alpha was detected in atherosclerotic patients. In this disease endothelial injuries appear, followed by a reduced release of nitric oxide (NO). Our results show that the vasoconstrictor effects of 8-iso-PGF2alpha as well as of 8-iso-PGE2 were amplified after endothelial damage of the vasculature of the isolated perfused rabbit ear. Also vasoconstrictions induced by both isoprostanes were amplified by perfusions with the NO-synthase blocker N(G)-nitro-L-arginine methylester (L-NAME) at a final concentration of 100 micromol/l. Therefore, we can assume that the amplification of the vasoconstrictor effects of the isoprostanes used after damage of endothelium might be mainly due to the reduced formation of NO.

1. The non-peptide bradykinin (BK) antagonist (E)-3-(6-acetamido-3-pyridyl)-N-[N-[2,4-dichloro-3-[(2-methyl-8-quinolin yl) oxymethyl]phenyl]-N-methylaminocarbonylmethyl]acrylamide (FR173657) was tested in intestinal, uterine, tracheal and vascular in vitro preparations. The investigation aimed at determining the antagonistic potency, duration of action, specificity for BK receptors and apparent mode of antagonistic action of FR173657. 2. Contractions of the isolated ileum of the guinea-pig in response to BK were inhibited by FR173657 (10-300 nM) in a concentration-dependent manner. The inhibition lasted for up to 90 min after wash-out of FR173657. Cumulative concentration-response curves to BK were shifted to the right with a concomitant decrease in the maximum effect. A pKB value of 8.7 was determined. FR173657 had no effect on contractions induced by acetylcholine, histamine, 5-hydroxytryptamine, substance P, angiotensin II or caerulein. 3. The concentration-response curves for B2 receptor-mediated relaxations of the rat isolated duodenum induced by BK were shifted to the right together with a concomitant reduction of the maximum BK effect in the presence of FR173657 (10-300 nM). A pKB of 9.0 +/- 0.2 was calculated. FR173657 had no effect on B1 receptor-mediated relaxations in response to des-Arg9-BK. 4. The concentration-response curves for BK-induced contractions of the rat isolated uterus were shifted to the right by FR173657 (3-300 nM) in a concentration-dependent and parallel manner. The Schild plot for the inhibition caused by FR173657 had a slope of -0.98 indicating a competitive mode of antagonism. A pA2 value of 9.1 was determined. 5. Contractions of the circular smooth muscles of the guinea-pig isolated trachea in response to BK were concentration-dependently inhibited by FR173657 (10-100 nM). An affinity estimate of 9.3 was calculated for FR173657. Contractions induced by acetylcholine and relaxations in response to isoprenaline remained completely unaffected by FR173657. 6. In the rabbit isolated perfused ear, BK (0.01-10 nmol) produced a dose-dependent vasoconstriction. In the presence of 30 nM FR173657, the effects of BK were reduced by at least 60%, while FR173657 completely abolished the effects of all BK doses at 300 nM. FR173657 did not affect vasoconstriction induced by noradrenaline or angiotensin II. 7. The arterial injection of BK (10 nmol) into the rabbit isolated perfused ear caused an approximately three fold increase in the release of the prostaglandins E2 and I2 into the venous effluent. The BK-stimulated prostaglandin release was completely abolished in the presence of FR173657 (300 nM) while the basal prostaglandin release was unchanged. 8. In summary, FR173657 was shown to be a highly potent and selective BK antagonist which was active on B2, but not B1, receptors. FR173657 was a competitive antagonist in the rat uterus but showed a deviation from competitive inhibition in the other preparations studied similar to other second generation peptide antagonists. The inhibitory action in vitro was long-lasting, but was fully reversible.

The isolated perfused rabbit ear was used to investigate the effect of eicosapentaenoic acid (EPA) on the vasoconstriction induced by noradrenaline (NA) and angiotensin II (A II). EPA (0.1, 1.0, 10.0 micrograms/ml) was shown to reduce the vasoconstriction (inhibition of flow) induced by NA in a dose-dependent manner. The dose-response curves of NA were shifted to the right. Emax of NA was reduced in particular at the highest concentration of EPA. The maximum effect of EPA developed slowly and reached a steady state after 150 min (0.1 microgram/ml EPA), 120 min (1.0 microgram/ml EPA), 100 min (3.0 microgram/ml EPA) and 60 min (10 micrograms/ml), respectively. In the presence of indomethacin (3 micrograms/ml), the vasoconstrictor effect of NA was not significantly influenced. The effect of EPA (3 micrograms/ml) was not reduced by indomethacin. In the presence of the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA, 10 micrograms/ml), the vasoconstrictor effect of NA was not significantly influenced. The effect of EPA (3 micrograms/ml) was not reduced by NDGA. Concomitant addition of indomethacin (3 micrograms/ml) and NDGA (10 micrograms/ml) also did not reduce the effect of EPA. EPA (3.0, 10.0 micrograms/ml) was shown to reduce also the vasoconstrictor effect of A II in the absence and the presence of the cyclooxygenase and lipoxygenase inhibitors. Determination by radioimmunoassay showed that the levels of thromboxane B2 (TXB2)-like immunoreactivity were below the detection limit in the perfusate of the ear. The levels of 6-keto-PGF1 alpha- and PGE2-like immunoreactivity in the perfusate were low. EPA reduced the concentration of 6-keto-PGF 1 alpha.(ABSTRACT TRUNCATED AT 250 WORDS)

The vasoconstrictor effect of neuropeptide Y (NPY) was compared with that of noradrenaline (NA) in the isolated perfused rabbit ear. Phentolamine at a concentration which completely abolished the effect of NA, did not diminish the effect of NPY. The combined vasoconstrictor effect of NPY and NA was significantly stronger than the calculated effect of an additive interaction, but not significantly stronger than an independent combination. This can be interpreted as an overadditive effect, and may be an indication for different points of attack with independent actions of these two transmitters in the vessels of the rabbit ear. Eicosapentaenoic acid (EPA) dose-dependently antagonized the effect of NPY to a similar degree as that of NA. In the presence of indomethacin (8.6 mumol/l), neither the effect of NPY nor that of EPA was changed. Moreover, EPA (33 mumol/l) diminished the combined vasoconstrictor effect of NA and NPY. These findings indicate that EPA is a non-selective antagonist of sympathetic transmitters in small peripheral vessels and excludes an interaction at specific receptors.