Chronic inhibition of NO synthase enhances the production of prostacyclin in coronary arteries through upregulation of the cyclooxygenase type 1 isoform

Abstract

We previously reported that chronic inhibition of NO synthase (NOS) in dogs leads to an upregulation of the cyclooxygenase (COX) pathway in the endothelium of the coronary artery after stimulation by bradykinin (BK) in vitro. The present experiments were designed to identify the nature of the COX isoform involved in this phenomenon. Rings of circumflex (LCX) and left anterior descending (LAD) coronary arteries were isolated from six control dogs and six dogs treated with the NOS-inhibitor, N omega-nitro-L-arginine (L-NNA, 30 mg/kg/d, i.v., during 7 days). Concentration-response curves to BK in U46619-contracted rings from LCX coronary arteries were constructed in the presence and absence of another NOS inhibitor (NG-monomethyl-L-arginine, L-NMMA), of selective inhibitors of the inducible isoform of COX (NS-398 and L-745,337) and of a non selective inhibitor of the inducible and constitutive isoforms of COX (indomethacin). Finally, measurements of 6-keto-prostaglandin F1 alpha, the stable metabolite of prostacyclin, were performed in the incubation medium by enzymo-immuno-assay on rings of isolated LAD coronary arteries in the presence and absence of the same inhibitors of COX, before and after stimulation by BK. In rings taken from control dogs, BK evoked a concentration-dependent relaxation (Emax: 115 +/- 10%; EC50: 8 +/- 4 nM). In the presence of L-NMMA, the concentration-relaxation curve to BK was significantly shifted to the right (Emax: 77 +/- 8%; EC50: 43 +/- 22 nM, P < 0.05). Addition of NS-398, L-745,337 and indomethacin to L-NMMA did not further modify the concentration-relaxation curve to BK. After chronic inhibition of NOS, the concentration-relaxation curve to BK was similar to that observed in rings taken from control dogs in the presence of L-NMMA (Emax: 75 +/- 5%; EC50: 69 +/- 36 nM). Addition of L-NMMA, alone or in combination with NS-398 or L-745,337 did not significantly modify this concentration-relaxation curve to BK. In contrast, the L-NMMA-indomethacin combination blunted the BK-induced relaxation of the coronary artery (Emax: 28 +/- 10%, P < 0.01). Basal release of prostacyclin was not different in rings taken from control and L-NNA treated dogs (56 +/- 16 vs 58 +/- 15 pg.mm-2). BK significantly increased this release but the increment was twofold greater in rings taken from L-NNA treated dogs than in rings taken from control dogs (P < 0.05). In rings taken from control and L-NNA treated dogs, the BK-stimulated production of prostacyclin observed in the presence of the solvent was not significantly modified by L-NMMA or the L-NMMA-L-745,337 combination. In contrast, the L-NMMA-indomethacin combination as well as endothelium removal completely suppressed the BK-stimulated production of prostacyclin. These findings demonstrate that in dogs submitted to chronic inhibition of NO synthesis (1) the residual relaxation to BK of canine isolated coronary arteries is mainly due to production of prostacyclin of endothelial origin, and (2) the enhancement of prostacyclin production by these vessels is ...

There^|^rsquo;s More to Flow-Mediated Dilation Than Nitric Oxide

“…Indeed, Osani et al 109) showed that inhibition of eNOS enhanced the production of PGI2 in response to shear stress, indicating that endogenous NO functions as an inhibitor of PGI2 production in an autocrine or paracrine fashion. This finding has been reported elsewhere [114][115][116][117] . The importance of PGI2 to conduit vessel dilation may also be altered with various diseased states and aging.…”

Chronic diet-induced hyperhomocysteinemia impairs eNOS regulation in mouse mesenteric arteries

“…Studies in which nitric oxide has been blocked pharmacologically or by genetic knockout of eNOS have shown a general compensation for the loss of nitric oxide by upregulation of EDHF or prostacyclin (4,6,16,27). General compensation by combined non-nitric oxide mechanisms is not indicated in the present study, because there is no difference in dilation between control and HHcy arteries with L-NAME (Fig.…”

Adaptation of the hypothalamic blood flow to chronic nitric oxide deficiency is independent of vasodilator prostanoids

“…Furthermore, the endothelium-dependent relaxation by bradykinin was sensitive to indomethacin in coronary arteries of dogs subjected to chronic NOS blockade but not in controls (Puybasset et al, 1996). A bradykinin-induced increase in prostacyclin production was greater in coronary arteries taken from nitro-L-arginine-treated dogs, which difference was attributable to the upregulation of the endothelial COX-1 isoform during chronic inhibition of NOS (Beverelli et al, 1997, Puybasset et al, 1996. The third conclusion of our present study is, however, that prostacyclin or other vasodilator prostanoids are not involved in the adaptation of the hypothalamic circulation to chronic NO deficiency.…”

“…In accordance, endothelial NOS (eNOS) knockout mice show normal blood flow in the heart (Gödecke et al, 1998) and brain (Atochin et al, 2003) indicating that the circulation of these organs is able to adapt to chronic NO deficiency. In case of the coronary circulation, it is well established that a vasodilator prostanoid, presumably prostacyclin, may function as a compensatory factor after the chronic loss of NO (Beverelli et al, 1997, Lacza et al, 2003Marcelín-Jiménez and Escalante, 2001;Puybasset et al, 1996). The mechanism of the adaptation of the cerebral circulation to chronic NO deficiency is far less understood.…”