Opposing roles of cyclic AMP in the vascular control of edema formation.

Eight agents that increase the intracellular concentration of cyclic AMP were tested for their effect on edema formation. The specificity of the agents for vascular smooth muscle or the endothelium was determined by measuring vasodilation with a laser Doppler flow probe and cAMP production by endothelial cells and vascular smooth muscle cells in culture. The agents were injected intradermally in anesthetized rabbit skin and the local accumulation of 125I-labeled albumin in response to intradermal bradykinin was measured. Iloprost, prostaglandin E1, prostaglandin E2, pituitary adenylate cyclase activating polypeptide (PACAP), and vasoactive intestinal polypeptide (VIP) potentiated bradykinin-induced edema. These same agents also increased blood flow and vascular smooth muscle cAMP concentrations, but did not increase endothelial cell cAMP production. Albuterol suppressed edema formation, did not cause vasodilation, but did increase endothelial cell cAMP concentrations. The phosphodiesterase inhibitor rolipram did not cause vasodilation, but suppressed edema and potentiated the cAMP response to albuterol in cultured endothelial cells. L-Isoproterenol affected both cell types. At a lower concentration L-isoproterenol was a potent stimulus to endothelial cell cAMP production and inhibited edema formation; a higher dose had additional effects on vascular smooth muscle and significantly increased blood flow. These findings support the hypothesis that increasing intracellular cAMP concentrations in vascular smooth muscle promotes edema via increased blood flow. In contrast, increasing cAMP concentrations in endothelium may suppress edema by enhancing the permeability barrier.

Involvement of nitric oxide synthase in the delayed vasodilator response to ultraviolet light irradiation of rat skin in vivo.

1. The role of nitric oxide synthase and cyclo-oxygenase in the skin blood flow response to ultraviolet light B (u.v.B) irradiation was investigated in the rat in vivo. 2. Local skin blood flow changes were measured in the shaved dorsal skin of anaesthetized male Sprague-Dawley rats with a laser Doppler flow probe. 3. u.v.B irradiation caused delayed onset vasodilation and by 18 h basal blood flow increased by 125 +/- 25% (P < 0.05, n = 12 rats, mean +/- s.e. mean). 4. Indomethacin, 3 nmol per site, NG-nitro-L-arginine methyl ester (L-NAME) 100 nmol per site, but not D-NAME 100 nmol per site, injected locally 17.5 h after u.v.B irradiation abolished the 18 h increase in blood flow. 5. The nitric oxide synthase inhibitor L-NAME, NG-monomethyl-L-arginine (L-NMMA) and canavanine, 10 and 100 nmol per site injected at 17.5 h, suppressed significantly the u.v.B 18 h response in a dose-dependent manner. The order of potency was L-NAME > canavanine = L-NMMA. The effect of L-NAME was reversed partially by the co-injection of an excess of L-arginine. 6. Topical application of the corticosteroid, clobetasol 17-propionate, immediately after irradiation inhibited the 18 h u.v.B response in a dose-dependent manner. 7. The delayed onset microcirculatory vasodilation induced by u.v.B involves both nitric oxide synthase and cyclo-oxygenase in this in vivo model. Topical corticosteroids may attenuate the response by inhibiting both prostaglandin and nitric oxide synthesis pathways.

Endotoxin-induced vasodilatation in anaesthetized rat skin involves nitric oxide and prostaglandin synthesis.

1. The effect of intradermally injected endotoxin on skin blood flow was investigated in anaesthetized male Wistar rats in vivo. 2. Local skin blood flow changes were measured hourly for 6 h in the shaved dorsal skin with a laser-Doppler flow probe and compared to changes in control sites which had been injected with 100 microliters of phosphate-buffered saline. By 3 h, skin blood flow increased above basal by 129 +/- 27% and 186 +/- 29% with 1 and 10 micrograms of endotoxin respectively. Blood flow remained significantly elevated at 6 h, the corresponding figures being 129 +/- 24% and 154 +/- 31% (P less than 0.05, n = 6 rats, mean +/- s.e.mean). 3. In further experiments, the response to 3 micrograms of endotoxin was measured at 4 h and treatment with a cyclo-oxygenase inhibitor, nitric oxide synthase inhibitors or a topical steroid all significantly inhibited this response (P less than 0.05 in each case, n = 6 rats in each group with duplicate sites in each animal). 4. Indomethacin 3 x 10(-9) mol per site injected 3.5 h after injection of endotoxin suppressed the mean 4 h response to endotoxin by 78%; NG-nitro-L-arginine methyl ester (L-NAME) 10(-7) mol per site suppressed the response by 95%; NG-monomethyl-L-arginine (L-NMMA) 10(-7) mol per site suppressed the response by 50%; whereas the D-isomer of NG-monomethyl-arginine 10(-7) mol per site had no significant effect.5. Topical application of the corticosteroid, betamethasone 17-valerate (1% solution) 18 h before injection of endotoxin inhibited the mean 4 h response to endotoxin by 66% and the 6 h response by 48%.6. In the same model, the vasodilator response to arachidonic acid was inhibited by both indomethacin and nitric oxide synthase inhibitors (P<0.05 in each case).7. These data suggest that the microcirculatory vasodilator response to endotoxin and arachidonic acid injected locally involves both nitric oxide synthase and cyclo-oxygenase in this in vivo model.