Recovery of prostacyclin production by de-endothelialized rabbit aorta. Critical role of neointimal smooth muscle cells

Prostacyclin Mitigates Renal Fibrosis by Activating Fibroblast Prostaglandin I 2 Receptor

SIGNIFICANCE STATEMENT

Renal fibrosis is a common pathologic process of progressive CKD. We have provided strong evidence that PGI 2 is an important component in the kidney injury/repairing process by reducing fibrosis and protecting renal function from declining. In our study, administration of a PGI 2 analog or selective PTGIR agonist after the acute injury ameliorated renal fibrosis. Our findings provide new insights into the role of PGI 2 in kidney biology and suggest that targeting PGI 2 /PTGIR may be a potential therapeutic strategy for CKD.

BACKGROUND

Prostanoids have been demonstrated to be important modulators to maintain tissue homeostasis in response to physiologic or pathophysiologic stress. Prostacyclin (PGI 2 ) is a member of prostanoids. While limited studies have shown that PGI 2 is involved in the tissue injury/repairing process, its role in renal fibrosis and CKD progression requires further investigation.

METHODS

Prostacyclin synthase ( Ptgis )-deficient mice, prostaglandin I 2 receptor ( Ptgir )-deficient mice, and an oral PGI 2 analog and selective PTGIR agonist were used to examine the role of PGI 2 in renal fibrosis in mouse models. We also analyzed the single-cell RNA-Seq data to examine the PTGIR -expressing cells in the kidneys of patients with CKD.

RESULTS

Increased PTGIS expression has been observed in fibrotic kidneys in both humans and mice. Deletion of the PTGIS gene aggravated renal fibrosis and decline of renal function in murine models. A PGI 2 analog or PTGIR agonist that was administered after the acute injury ameliorated renal fibrosis. PTGIR, the PGI 2 receptor, deficiency blunted the protective effect of the PGI 2 analog. Fibroblasts and myofibroblasts were the major cell types expressing PTGIR in the kidneys of patients with CKD. Deletion of PTGIR in collagen-producing fibroblastic cells aggravated renal fibrosis. The protective effect of PGI 2 was associated with the inhibition of fibroblast activation through PTGIR-mediated signaling.

CONCLUSIONS

PGI 2 is an important component in the kidney injury/repairing process by preventing the overactivation of fibroblasts during the repairing process and protecting the kidney from fibrosis and decline of renal function. Our findings suggest that PGI 2 /PTGIR is a potential therapeutic target for CKD.

Cyclooxygenase Activity in the Thoracoabdominal Aorta After 24 Hours of Intraaortic Balloon Counterpulsation: An Assessment of the Effects of Localized Mechanical Trauma

Using a canine model, the authors evaluated the effects of twenty-four hours of intraaortic balloon counterpulsation (IABCP) on the morphology of the thoracoabdominal aorta and its spontaneous and arachidonate stimulated pro duction of prostacyclin (PGI2). The treated group was counter-pulsed at a 1:1 ratio with a 40 cc balloon. The control group had the balloon inserted and left deflated across the thoracoabdominal aorta.

There were no differences between the IABCP or sham groups in prostanoid production either in the thoracic or abdominal aorta. Baseline PGI2 production in the control versus treated group of thoracic aortas was 1880 ± 1140 pg/cm2/ min vs 1992 ± 1125. The stimulated response in the control group, 9180 ± 1198, was statistically different from baseline (P < .001). The stimulated in crease in the IABCP group, 6269 ± 5240, relative to baseline was also signifi cant (P < .01). There were no significant differences, either between or within groups in the abdominal aortas. Poststimulation values (30 min) were signifi cantly below baseline in each group in each section of the aorta (P < .05). Light microscopy showed a statistically significant difference in endothelial preserva tion between the control and the balloon group, 66 ± 25% vs 19 ± 17% (P < 0.05) .

The authors conclude that IABCP results in severe endothelial destruction but that spontaneous and stimulated PGI2 production is unimpaired. It remains to be determined whether the aorta may sustain long-term damage due to the repair process after IABCP.

Effect of cardioplegic and organ preservation solutions and their components on coronary endothelium-derived relaxing factors

Cardioplegic (and organ preservation) solutions were initially designed to protect the myocardium (cardiac myocytes) during cardiac operation (and heart transplantation). Because of differences between cardiac myocytes and vascular (endothelial and smooth muscle) cells in structure and function, the solutions may have an adverse effect on coronary vascular cells. However, such effect is often complicated by many other factors such as ischemia-reperfusion injury, temperature, and perfusion pressure or duration. To evaluate the effect of a solution on the coronary endothelial function, a number of points should be taken into consideration. First, the overall effect on endothelium should be identified. Second, the effect of the solution on the individual endothelium-derived relaxing factors (nitric oxide, prostacyclin, and endothelium-derived hyperpolarizing factor) must be distinguished. Third, the effect of each major component of the solution should be investigated. Lastly, the effect of a variety of new additives in the solution may be studied. Based on available literature these issues are reviewed to provide information for further development of cardioplegic or organ preservation solutions.

Effects of oral beraprost sodium, a prostaglandin I2 analogue, on endothelium dependent vasodilatation in the forearm of patients with coronary artery disease

1. Previous clinical studies with prostaglandin I(2) (PGI(2)) analogue beraprost sodium suggested the potential effects on protection of cardiovascular events in patients with peripheral artery disease. Although the mechanism is not well known, experimental studies have shown protective effects of endothelial cells. This study was designed to examine the effects of beraprost sodium on vascular endothelial function in the forearm of patients with coronary artery disease. 2. Beraprost sodium (120 microg/day) was orally administered to 14 coronary artery disease patients for 4 weeks and then stopped for 4 weeks. Eleven control patients did not receive beraprost sodium treatment. Reactive hyperemia was induced in the forearm, endothelium-dependent vasodilatation was assessed by plethysmography, and urinary 8-iso-prostaglandin F(2alpha) (8-iso-PGF(2alpha)) was measured at baseline, 4 weeks and 8 weeks. 3. Both groups had similar reactive hyperemic responses at baseline. In the control group, reactive hyperemic response and urinary 8-iso-PGF(2alpha) remained unchanged for 8 weeks. In the beraprost group, maximum forearm blood flow increased significantly (P = 0.01) after 4 weeks of treatment and returned to baseline at 8 weeks. Duration of hyperemia increased significantly (P = 0.003) after 4 weeks, and remained greater than baseline at 8 weeks (P = 0.02). Urinary 8-iso-PGF(2alpha) decreased significantly (P = 0.03) after 4 weeks, and tended to be lower at 8 weeks (P = 0.07). Changes in reactive hyperemia correlated weakly but significantly with changes in 8-iso-PGF(2alpha) (P < 0.001). 4. Beraprost sodium decreased oxidative stress and improved forearm endothelium-dependent vasodilatation in coronary artery disease patients. The favorable effects on vascular endothelium could potentially lead to a decrease in vascular events.

COX-2 inhibitors selectively block prostacyclin synthesis in endotoxin-exposed vascular smooth muscle cells

High levels of prostacyclin (PGI2; measured as 6-keto-PGF1alpha) have been reported in patients under septic shock. Because this was at variance with our previous findings of nitration and inhibition of PGI2 synthase by endotoxin (LPS) in the endothelium, we examined the role of vascular smooth muscle as an alternative source of PGI2. Bovine aortic smooth muscle cells (SMC) in passage 1 contained high levels of PGI2 synthase but no activity and no detectable levels of COX-1 or COX-2. LPS exposure for 3 h caused COX-2 mRNA and protein levels to rise during 8 h together with a large increase in PGI2 synthase activity. In contrast, cytokines lead to only a moderate increase of both PGI2 and PGE2. Specific COX-2 inhibitors completely blocked PGI2 formation but PGE2 synthesis only partially. Unexpectedly, *NO formation remained low over 6-8 h, which may be a reason for the lack of nitration and inhibition of prostacyclin synthase in LPS exposed SMC. Our results can explain the clinical observation of severe hypotension in progressive stages of septic shock as a mechanism to compensate endothelial dysfunction. According to our data, the use of COX-2-specific inhibitors may not be advisable in septic patients. In contrast, administration of COX-1-specific blockers could prevent platelet aggregation during progressed stages of endotoxic shock.

Experimental and interventional dietary study in humans on the role of HDL fatty acid composition in PGI2 release and Cox-2 expression by VSMC

BACKGROUND

High-density lipoproteins (HDLs) induce prostacyclin (PGI2) release in vascular smooth muscle cells (VSMCs) by up-regulation of cyclooxygenase-2 (Cox-2). Our goal was to analyze the role of human HDL lipid moiety on Cox-2-dependent PGI2 synthesis in human VSMCs and to assess the impact that the intake of diets with different fatty acid composition exert on HDL-induced PGI2 release.

MATERIALS AND METHODS

Human VSMCs were treated with HDL or fatty acids in the presence or absence of different cell signalling inhibitors and PGI2 (by enzyme immunoassay) and Cox-2 protein levels (by Western blot) were analyzed. High-density lipoproteins were obtained from a plasma pool or from plasma of 12 volunteers subjected to a longitudinal dietary interventional study of three consecutive diets periods enriched in monounsaturated fatty acids (MUFAs), polyunsaturated fatty acids n-6 (PUFA n-6) or n-3 (PUFA n-3).

RESULTS

High-density lipoprotein delipidation attenuated the effect of HDL on both PGI2 synthesis and Cox-2 up-regulation, while arachidonic acid (AA) but not other fatty acids mimicked the effects of HDL. Arachidonic acid induced PGI2 synthesis and Cox-2 expression through similar mechanisms to those activated by HDL [pertussis toxin-sensitive G proteins, p42/44 mitogen-activated protein kinase (MAPK), p38MAPK, and c-Jun N-terminal kinase-1 (JNK-1) pathways]. Finally, we observed that HDL from the PUFA n-3 dietary period induced lower PGI2 release than that from the PUFA n-6 period (64% vs. 100%).

CONCLUSIONS

Our results suggest that lipid moiety modulates HDL-induced PGI2 release/Cox-2 up-regulation in human VSMCs, and that changes in fatty acids as accomplished with the diet can modulate vascular PGI2 homeostasis.

Biologic degeneration of vein grafts after thrombotic occlusion: thrombectomy within 3 days results in better indices of viability

OBJECTIVES

To clarify the mechanism for poor patency of vein grafts after thrombectomy and the time limit for successful salvage operation, we investigated the time course of biologic degenerative changes in thrombosed vein grafts. Materials and methods The right femoral artery was replaced with a femoral vein graft in 25 mongrel dogs. After 3 months, grafts were explanted in 5 dogs (control grafts), and the remaining 20 dogs underwent femoral artery ligation to create a thrombosed graft. Of the 20 grafts, 5 were explanted at 3 days after ligation (group I-3) and 5 were explanted at 5 days after ligation (group I-5). Of the remaining 10 grafts, 5 underwent thrombectomy at 3 days after ligation (group II-3) and 5 underwent thrombectomy at 5 days after ligation, and were reimplanted into the left femoral artery, then explanted 28 days after reimplantation. The grafts were assessed with immunohistochemistry and prostaglandin (PG) I(2) assay (6-keto-PGI(1alpha)).

RESULTS

Of the 25 grafts, occlusion recurred in 3 in group II-5 within 28 days after reimplantation. There were significant differences between group I-5 and group I-3 or control grafts for percentage of areas positive for alpha-actin, total number of cells per field, and proliferating cell nuclear antigen (PCNA)-positive cells in layer of thickened intima and atrophied media (I/M), and for total cell and PCNA- positive cell numbers per field in the adventitia. Mean 6-ketoPGF(1alpha) was 40 +/- 14.1 pg/mg/min in control dogs, 84 +/- 18.9 pg/mg/min in group I-3, and 15.4 +/- 7.7 pg/mg/min in group I-5, demonstrating a significant reduction in group I-5 (P =.009).

CONCLUSION

Graft wall cell viability and PGI(2) production in thrombosed vein grafts are well preserved for up to 3 days. Therefore graft salvage operations no later than 3 days after thrombotic occlusion may provide acceptable long-term patency of salvaged grafts.

Regulatory effects of HDL on smooth muscle cell prostacyclin release

One mechanism by which high density lipoproteins (HDLs) exert their protective effect against coronary artery disease could be related to the induction of prostacyclin (PGI(2)) release in the vessel wall. We have recently shown that HDL increases PGI(2) production in rabbit smooth muscle cells (RSMCs) and that this increase is dependent on cyclooxygenase-2 (Cox-2). Here we analyze the mechanism by which rabbit HDL induces PGI(2) release in RSMCs. Our results show that although HDL(2) and HDL(3) share a similar capacity to induce Cox-2 protein levels, HDL(3) stimulates a higher PGI(2) release than does HDL(2), probably because of their relative arachidonate contents. Acetylsalicylic acid pretreatment (300 micromol/L, 30 minutes) significantly reduced the HDL-induced PGI(2) release, suggesting that both preexisting and induced Cox-2 activities were involved in the HDL effect. Ca(2+)-dependent cytosolic phospholipase A(2) (cPLA(2)) and Cox-1 protein levels were not altered by HDL. Dexamethasone (2 micromol/L), which also inhibited the HDL-induced PGI(2) release, reduced significantly both Cox-2 mRNA and protein levels without affecting cPLA(2) and Cox-1 protein levels. In addition, methylarachidonyl fluorophosphonate, a potent inhibitor of cPLA(2), did not produce any effect on HDL-induced PGI(2) release. In the presence of cycloheximide, Cox-2 mRNA levels were induced by HDL and inhibited by dexamethasone, suggesting that HDL and dexamethasone work in the absence of de novo protein synthesis. These results indicate an early effect of HDL on PGI(2) biosynthesis, specifically increasing Cox-2. PD98059, an inhibitor of mitogen-activated protein kinase kinase, completely inhibited HDL-induced PGI(2) release, whereas GF109203X, a protein kinase C inhibitor, had no effect. Thus, HDL induces PGI(2) synthesis by a mechanism dependent on the mitogen-activated protein kinase pathway but independent of protein kinase C.

Role of medial smooth muscle cell function in antithrombogenicity of vein grafts

OBJECTIVES

To determine the significance of prostaglandin I2 (PGI2) production by medial smooth muscle cells (SMCs), we assessed PGI2 production from denuded vein grafts and their antithrombogenicity.

MATERIALS AND METHODS

A total of 30 dogs were divided into two groups: in group I, 14 dogs (27 veins, 188 segments) were used to assay PGI2 production, which was measured as 6-keto-PGF1 alpha. In group II, 16 dogs were used for an implantation study and the thrombus-free surface (TFS) score was calculated 24 h after implantation. Both groups contained the following subgroups: subgroup A, freshly harvested veins; subgroup B, endothelial denuded veins; subgroup C, veins frozen and cryopreserved; subgroup D, veins treated with protease.

RESULTS

Values of 6-keto-PGF1 alpha (pg/mg/min) for basal and stimulated states in subgroup I-A through I-D were 58.0 +/- 8.9 and 530.6 +/- 74.7, 26.3 +/- 4.7 and 82.3 +/- 11.4, 17.9 +/- 1.3 and 39.4 +/- 3.3, and 13.3 +/- 1.8 and 32.2 +/- 6.2, respectively. The PGI2 production in subgroup I-A were significantly higher than those in the other three subgroups (p < 0.01 for basal and stimulated), while the production in subgroup I-B was also significantly higher than those in the remaining two (p < 0.05 for basal and stimulated). The TFS scores in subgroup II-A through II-D were 98 +/- 2%, 90 +/- 2%, 38 +/- 5%, and 15 +/- 7%, respectively, showing significantly superior antithrombogenicity in subgroup II-B, as well as in II-A, when compared with the remaining two (p = 0.014).

CONCLUSION

The amount of PGI2 generated by the medial SMCs may be sufficient for maintaining the antithrombogenicity of the endothelial denuded AVGs.

Towards the prevention of vein graft failure

Improved outcome after coronary bypass surgery over the last decade has been attributed largely to the increasing use of arterial conduits and their superior patency rates over that of saphenous vein grafts. In spite of this trend, autologous saphenous vein has remained an important and convenient conduit for a variety of operative scenarios, and is still used for more than 70% of grafts. As a result, vein graft failure continues to represent a significant clinical and economic burden upon the health care service. Between 15 to 30% of saphenous vein grafts occlude within the first year of surgery, increasing to over 50% after 10 years. By this time, more than 10% of patients will require further intervention to alleviate symptoms arising from occluded grafts and progression of native disease. Graft occlusion arises either from early thrombosis or the later onset of 'vein graft disease' and subsequent atherosclerotic changes.

Induction of cyclooxygenase-2 in human saphenous vein and internal mammary artery

Within vessels, cyclooxygenase (COX) is expressed constitutively (COX-1) in endothelial cells where its production of prostacyclin is thought to contribute to the maintenance of vascular integrity. Recently, a novel isoform of COX, COX-2, has been described that is induced in animal arterial vessels after physical damage or exposure to proinflammatory cytokines. However, induction of COX-2 in human vessels has not been characterized. Moreover, the relative ability of arteries and veins to express COX-2 has not been addressed. Thus, we have compared the ability of segments of human saphenous vein and internal mammary artery, obtained from the same patient, to express COX-2 activity and mRNA after organ culture in the presence and absence of interleukin-1 beta. COX-2 metabolites, measured by radioimmunoassay, were released by both the internal mammary artery and saphenous vein in the following rank order: prostaglandin E2 > or = prostacyclin thromboxane A2. Inclusion of interleukin-1 beta in the culture medium increased the release of prostanoids by the saphenous vein but not by the internal mammary artery. However, the selective COX-2 inhibitor NS-398 significantly attenuated prostacyclin release from both tissues. Northern blot analysis showed no detectable COX-2 mRNA in freshly prepared saphenous vein or internal mammary artery. In contrast, after 48 hours in organ culture, low levels of COX-2 mRNA were detected in both internal mammary artery and saphenous vein, an effect that was greatly increased by interleukin-1 beta. These observations show that COX-2 is induced in human saphenous vein and internal mammary artery and suggest that this may occur in humans after coronary artery bypass graft surgery. The induction of COX-2 and subsequent release of prostacyclin may represent an endogenous defense mechanism against endothelial damage incurred during surgical preparation of these vessels for bypass.

Characterization of the induction of nitric oxide synthase and cyclo-oxygenase in rat aorta in organ culture

1. Within vessels, the formation of nitric oxide (NO) or prostaglandins is normally catalysed in the endothelium by constitutive isoforms of NO synthase (eNOS) and cyclo-oxygenase (COX-1), respectively. However, during inflammatory conditions, the underlying smooth muscle acquires the ability to release NO and prostaglandins after the expression of inducible isoforms of NOS (iNOS) and COX (COX-2). The co-induction of iNOS and COX-2 has been studied over 24 h in isolated vascular smooth muscle cells in vitro. However, due to the limitation of using cultured cells, the relationship between the activities of iNOS and COX over longer periods has not been addressed. Moreover, the relative contribution of the endothelium to the production of NO and prostaglandins under inflammatory conditions is not completely understood. 2. Here using an organ culture system, we have determined the profile of COX (6-keto prostaglandin F1 alpha (6-keto PGF1 alpha), PGE2, thromboxane B2 (TXB2) and NOS (nitrite and nitrate) metabolites released over a period of 10 days from segments of rat aorta. In each case, segments from the same animal were left untreated or treated with bacterial lipopolysaccharide (LPS; 10 micrograms ml-1) in order to induce iNOS and COX-2. Prostaglandins were measured by radioimmunoassay whilst nitrite and nitrate were measured, respectively, by Greiss reaction alone, or following a nitrate reductase step. The isoforms of NOS and COX responsible for metabolite release were characterized pharmacologically by use of inhibitors and at the molecular level by reverse transcription polymerase chain reaction with specific primers for iNOS, eNOS, COX-1 and COX-2. In separate experiments the role of the endothelium in the release of nitrite, nitrate and prostaglandins and in the expression of iNOS, eNOS, COX-1 and COX-2 was determined by comparing responses in endothelium denuded and endothelium-intact segments of rat aorta. 3. Under control culture conditions vessels released prostaglandins in the following rank order 6-keto PGF1 alpha = PGE2 > > TXB2. LPS increased the release of 6-keto PGF1 alpha and PGE2 but not of TXB2, an effect that was inhibited by the protein synthesis inhibitor cycloheximide (1 microM), the anti-inflammatory steroid dexamethason (1 microM), the nonsteroidal anti-inflammatory drug indomethacin (30 microM) and, where tested, the selective COX-2 inhibitor NS-398 (30 microM). Similarly, segments of rat aorta released detectable levels of nitrite and nitrate, which were reduced by NG-nitro-L-arginine methyl ester (L-NAME, 1 mM), which inhibits all isoforms of NOS, and by dexamethasone (1 microM), which inhibits the induction of iNOS. The proportion of nitrate to nitrite released over the 10 day period varied greatly from approximately 1:1 on days 5 to 8 to 5:1 on day 9. However, the sum of nitrite and nitrate (NOx) as well as PGE2 remained elevated over the whole 10 day period. The formation of 6-keto PGF1 alpha peaked on days 1 and 2. 4. In freshly prepared tissue, mRNAs for eNOS, COX-1, iNOS and COX-2 were detected. After 24 h in culture, there was an apparent increase in the level of mRNAs for iNOS and COX-2 but not for eNOS or COX-1, an effect that was further enhanced when LPS was included in the culture medium. The expressions of mRNA for eNOS, COX-1, iNOS or COX-2 were not greatly different in vessels with intact or disrupted endothelium. Similarly the release of NOx or PGE2 by vessels after the 1st or 9th day in culture were not significantly different from vessels prepared with or without endothelium. 5. Thus, COX-2 and iNOS are co-induced in intact vessels in culture, with the vascular smooth muscle being the main site of mediator generation. In contrast to data from isolated cells in culture (observed usually over 1 day), both COX and NOS activities in cultured blood vessels were elevated for at least 10 days. Also, unlike isolated cells in culture, the COX and NOS pathways were active independently; L-NAME had little effect on the activity of COX and indomethacin had little effect on the activity of NOS.

Roles of vasodilatory prostaglandins in mitogenesis of vascular smooth muscle cells

Vasodilatory prostaglandins (PGI2, PGE1) and synthetic prostacyclin mimetics inhibit smooth muscle cell proliferation in vitro after stimulation by growth factors. Similar results are obtained in vivo after endothelial injury, suggesting that vasodilatory prostaglandins might also control smooth muscle cell proliferation in vivo. However, available data from clinical trials are conflicting and currently do not support the concept that these compounds might be successfully used to suppress excessive smooth muscle cell growth in response to tissue injury, specifically restenosis after PTCA. One possible explanation for these different results is an agonist-induced down-regulation of prostacyclin receptors in vascular smooth muscle cells. It is possible that enhanced endogenous prostacyclin biosynthesis, subsequent to induction of COX-2 and/or in relation to the formation of a neointima from media smooth muscle cells, might have a similar effect. There is still uncertainty regarding the cellular signal transduction pathways and their possibly complex interaction, although cAMP-dependent reactions are probably involved. In addition, vasodilatory prostaglandins might also interfere with the generation and action of other growth modulating factors, including PDGF, hepatocyte growth factor and nitric oxide. In conclusion, vasodilatory prostaglandins might be considered as growth modulating endogenous mediators in vascular smooth muscle cells.

Mechanism of hydroxyl radical-induced modulation of vascular tone

We investigated the effects of hydroxyl radicals (OH) generated by a .OH-generating system (dihydroxyfumarate [DHF], adenosine diphosphate [ADP], and FeCl3) on isolated rabbit aorta suspended in Krebs-Ringer solution. The .OH-generating system produced a concentration-dependent generation of .OH. .OH relaxed rabbit aorta and norepinephrine (NE)-precontracted aorta in a concentration-dependent manner. Mannitol completely prevented this relaxation. Relaxation was completely absent in preparations denuded of endothelium. The relaxant effect was reduced by 62% by an inhibitor of nitric oxide synthesis (NG-monomethyl-L-arginine), by 58% by an inhibitor of guanylate cyclase (methylene blue), by 48% by an inhibitor of cyclooxygenase (indomethacin), and by 83% by an adenosine triphosphate (ATP)-sensitive K+ channel blocker (glyburide). The inhibition of .OH-induced relaxation by a combination of indomethacin, methylene blue, and glyburide was not greater than by each of the individual agents. These results indicate that .OH produces a relaxation of the aorta that is completely endothelium-dependent and is partly mediated by an endothelium-derived relaxing factor (nitric oxide), vasodilatory arachidonic acid metabolites, and an ATP-sensitive K+ channel.

The effect of thrombus on the vascular endothelium of arterialized vein grafts

BACKGROUND

It is known that vein grafts can be salvaged by clot removal, but patency rates are diminished. This study was designed to determine the effects of thrombus on vascular endothelium and the ability of the endothelium to recover normal function.

METHODS

Thirty external jugular vein grafts were placed as bilateral femoral artery interposition grafts in 15 mongrel dogs and allowed to arterialize for a period of at least 12 weeks. Six control grafts were not exposed to thrombus (C-NT). Six other control grafts were exposed to thrombus for 7 days and removed, ie, allowed no in vivo recovery (C-T). The remaining 18 grafts in 9 canines were exposed to autologous thrombus for 5 days and then flow was restored. The right femoral graft was removed 7 days after thrombectomy and the left removed 30 days after thrombectomy. At the time of removal, the grafts were perfused with a balanced salt solution alone and then with arachidonic acid added to the same volume of the salt solution. Perfusates were collected at 5, 15, and 30 minutes. These perfusates were assayed for the presence of 6-keto-prosglandin F1 alpha (6-keto-PGF1(1 alpha)), a metabolite of prostacyclin (PGI2). Over the 30-day recovery period, the amounts of 6-keto-PGF1(1 alpha) produced with and without arachidonic acid added were compared to assess endothelial response. Electron micrographs of the endothelium of all vein grafts were compared to the assay findings.

RESULTS

When arachidonic acid was added to the perfusion system, there was a several fold increase in the production of 6-keto-PGF1(1 alpha) over baseline in all grafts allowed recovery. Grafts (C-T) that were allowed no in vivo recovery had no response to arachidonic acid. Ratios of 6-keto-PGF1(1 alpha) production with arachidonic acid stimulation to 6-keto-PGF1(1 alpha) production without stimulation were calculated to compare endothelial function. The electron micrographs showed the vascular endothelium to be severely injured after contact with thrombus, but recovered by 7 days.

CONCLUSIONS

This study suggests that the endothelium of canine vein grafts is injured by contact with thrombus for 5 days but can recover structure and function. This recovery is detectable at 7 days post-thrombectomy.

Prostacyclin production at the human microvascular anastomosis: its effect on initial platelet deposition

The human microvascular anastomosis represents a localized environment with strongly thrombotic tendencies. In previous studies, an increase in initial platelet deposition at a human ex vivo anastomosis was measured. It is postulated that this increase in anastomotic platelet deposition was due to a reduction in anastomotic prostacyclin production as a consequence of local endothelial cell injury or loss. Instead, in this study, an increase in anastomotic prostacyclin production over unsutured controls (control 1093 +/- 222 pg/ml of 6-keto prostaglandin F (PGF) 1-alpha, n=21; anastomosis 2494 +/- 414, n=21, mean +/- 1 SEM, p=0.005) is demonstrated. Anastomotic prostacyclin production was augmented by addition of arachidonic acid (0.1 mM) (39,000 +/- 11,300 pg/ml of 6-keto PGF 1-alpha, n=7, p<0.001) and suppressed by the preincubation of vessel segments with aspirin in a dose-dependent fashion (1mM) (83+/-22 pg/ml of 6-keto PGF 1-alpha, n=21, p<0.001); aspirin (0.1 mM) (312 +/- 56 pg/ml of 6-keto PGF 1-alpha, n=7, p<0.001). In further studies using a perfusion apparatus of human blood pumped through human placental artery segments, suppression of prostacyclin production did not augment initial platelet deposition (control anastomosis 4.9 +/- 2.2 x10(6) platelets per cm2, aspirin treatment 6.0 +/- 2.8 x 10(6) platelets per cm2, n=5, mean +/- 1 SEM, p>0.05). Suppression of platelet function with aspirin (0.1 mM) also did not decrease initial platelet deposition onto the anastomosis (5.8 +/- 2.8 x 10(6) platelets per cm2, n=r, p>0.05). In this model system, initial platelet deposition at the anastomosis may not be dependent upon cyclooxygenase pathways.

Migration of arterial wall cells. Expression of plasminogen activators and inhibitors in injured rat arteries

The expression of plasminogen activators and inhibitors was examined in denuded arteries. Within 5 days, smooth muscle cells (SMCs) on the luminal surface expressed the mRNA for tissue-type plasminogen activator (TPA), urokinase type plasminogen (UPA), the receptor for UPA (UPAR), and plasminogen activator inhibitor type-1 (PAI-1). Similar results were seen after 8 days. Six weeks later, only TPA mRNA was still expressed by SMCs on the luminal surface. En face casein zymograms revealed a net fibrinolytic activity in areas covered with luminal SMCs. Reverse zymography showed no antifibrinolytic activity in these zones. Quiescent endothelial cells did not express TPA, UPA, UPAR, or PAI-1 mRNA. Regenerating endothelium at the wound edge strongly expressed TPA. UPA, and UPAR, as well as PAI-1. UPA and UPAR expression was highly restricted to cells at the wound edge and was not present elsewhere. En face zymography showed no plasmin activity in endothelialized areas, and reverse zymography showed a net fibrinolytic activity in endothelialized zones. These results suggest that plasminogen activator and inhibitor expression correlates with the migration of both SMCs and endothelial cells into an arterial wound.

Inhibition by beraprost sodium of thrombin-induced increase in endothelial macromolecular permeability

Effect of beraprost sodium (BPS), a long-acting and orally active stable analogue of PGI2, on the macromolecular permeability of cultured vascular endothelial cells (HUVEC) was detected by the transport of FITC-albumin. Thrombin treatment resulted in induction of FITC-albumin transport across the endothelial cell monolayer. The albumin transport induced by thrombin was not accompanied by any damage to the cells. BPS had no effect on the permeability of resting endothelial monolayers, while BPS inhibited the thrombin-induced increase in the albumin permeability in a dose-dependent manner (30-1000 nM). Treatment of the cells with PGI2 or dibutyryl cAMP caused a significant inhibition of the thrombin-induced increase in the albumin permeability. These results strongly suggested that BPS suppressed the thrombin-induced macromolecular permeability in HUVEC through the elevation of its intracellular cAMP, and that BPS was a suppressor against inflammatory vascular changes such as exudation.

Distension produces medial but not endothelial damage in porcine internal mammary artery

The influence of intraluminal distension on porcine internal mammary artery was studied using adenosine 5'-triphosphate (ATP) concentration and prostacyclin production as biochemical markers of medial and endothelial functional integrity respectively. Distension reduced mean (95% confidence limits) tissue ATP concentrations from 459 (337-581) nmol/g wet weight to 314 (193-435) nmol/g wet weight (n = 10, P < 0.01). Stimulated prostacyclin production was similar in undistended (25.8(15.9-35.9) pg/min per mg wet weight) and distended arteries (33.2(21.4-45.1) pg/min per mg wet weight) (n = 8, not significant). The data demonstrate that distension of the internal mammary artery results in acute medial but not endothelial damage. Distension-induced medial damage is unlikely to be rapidly reversible and might have implications for the early and long-term function of the artery as a bypass graft.

Use of prostaglandin I2 analog in treatment of massive hepatic necrosis associated with endothelial cell injury and diffuse sinusoidal fibrin deposition

Endothelial cell damage causes massive hepatic necrosis as a result of fibrin deposition in the hepatic sinusoids. When a stable analog of prostaglandin I2, beraprost sodium, was administered to rats given either dimethylnitrosamine, carbon tetrachloride, or endotoxin following Corynebacterium parvum administration, the hepatic necrosis produced in each was attenuated, but to a greater extent in the dimethylnitrosamine and endotoxin/Corynebacterium parvum models, where fibrin deposition in the hepatic sinusoids occurs, as compared to the carbon tetrachloride model, where such fibrin deposition does not occur. Beraprost sodium reduced the expected increase of portal venous pressure in the endotoxin/Corynebacterium parvum model without affecting plasma thrombin-antithrombin III complex levels. Beraprost sodium also significantly reduced cell killing of both isolated rat hepatocytes and hepatic sinusoidal endothelial cells exposed to tert-butyl hydroperoxide when compared to controls. Beraprost sodium could prove to be a therapeutic candidate for the treatment of hepatic necrosis, particularly in cases associated with fibrin deposition in the hepatic sinusoids because of its fibrin clot-clearing action.

Effects of a thromboxane A2-receptor antagonist, a thromboxane synthetase inhibitor and aspirin on prostaglandin I2 production in endothelium-intact and -injured aorta of guinea pigs

We examined the effects of KW-3635, a thromboxane (TX) A2-receptor antagonist, and OKY-046, a TX synthetase inhibitor, on the prostaglandin (PG) I2 production in endothelium-intact and -injured guinea pig aorta and compared them with those of aspirin. In the endothelium-intact aorta, both the low (3 mg/kg) and the high (100 mg/kg) dose of aspirin similarly reduced the PGI2 production, as measured ex vivo 1 hr after the injury. In contrast, neither KW-3635 (10 mg/kg) nor OKY-046 (30 mg/kg) inhibited the PGI2 production. The endothelial injury, induced by balloon catheterization, caused a reduction of PGI2 production in the aorta and decline of plasma PGI2/TXA2 ratio. In the endothelium-injured animals, the high dose of aspirin further reduced the PGI2 production in the aorta, whereas KW-3635 and OKY-046 did not affect it. KW-3635 and OKY-046 also ameliorated the reduced ratio of PGI2/TXA2 in the plasma. The present results demonstrate that aspirin, but not KW-3635 or OKY-046, reduces the PGI2 production in the aorta either in the endothelium-intact or -injured state. It is thus suggested that the TXA2-receptor antagonist and the TX synthetase inhibitor have some advantages over aspirin when used for the prevention of acute thrombosis after percutaneous transluminal angioplasty.

Regional differences in prostaglandin production rates among porcine intrathoracic vessels

To investigate the regional variability in intrathoracic vascular prostaglandin (PG) synthesis, we obtained vessel segments from porcine coronary artery (COA), thoracic aorta (AT), common carotid artery (CRA), pulmonary artery (PA), pulmonary vein (PV), and inferior vena cava (IVC). Vascular production rates of 6-keto-PGF1 alpha (an indicator for PGI2), PGF2 alpha, and PGE2 were measured both in unstimulated state and in arachidonic acid-stimulated state using immunosorbent assays. Our results indicated that PGI2 production rate in all vessel segments decayed with time after vessel dissection. In all vessel segments tested under unstimulated conditions, PGI2 production rates were about one order of magnitude higher than PGF2 alpha and PGE2 production rates of the same specimens. Results from unstimulated, 1.5 hr pre-incubated specimens indicated that i) PGI2 production rates in COA, AT, and PV were greater than those in CRA, PA, and IVC; ii) PGF2 alpha production rates from the same specimens were higher in PV than in AT, CRA, and IVC, while these in PA were higher than in IVC; and iii) PGE2 production rates from the same specimens were not significantly different from one another. Arachidonic acid added at about 1.5 hr after vessel harvest stimulated the PGI2 and PGF2 alpha synthesis rates by 3 to 15 folds. However, this arachidonic acid treatment caused 70 to 300-fold increases in PGE2 production rates, reaching levels comparable to PGI2. All three prostanoid production rates under stimulated conditions were also variable among different intrathoracic vessels. Although either physiological gas concentrations or local hemodynamic conditions alone can partially explain our results, which physiological parameter(s) actually causes these regional differences remains to be verified.

Endothelium-derived nitric oxide protection of spontaneous coronary contractions in the rabbit by countering Ca2+ influx via the voltage-sensitive Ca2+ channel

The mechanism of spontaneous coronary contractions was investigated in the rabbit. Arteries with intact endothelium did not spontaneously contract. However, spontaneous coronary contractions were generated after the removal of the endothelium. NG-nitro-L-arginine methyl ester and methylene blue, the inhibitors of the formation and the action of nitric oxide, respectively, induced contractions in endothelium-intact arteries. Spontaneously produced contractions in endothelium-denuded arteries were reversibly inhibited by a Ca(2+)-free solution and by nifedipine, but not by inhibitors of neurotransmitters or prostanoids. These findings may indicate that spontaneous coronary contractions in the rabbit may be attributed to Ca2+ influx via the voltage-sensitive Ca2+ channel. The basal release of endothelium-derived nitric oxide may, in part, antagonize this Ca2+ influx.

Vessel repair after balloon angioplasty: morphological appearance and prostacyclin synthesising capacity

Immediately after balloon dilatation of the rabbit aorta the release of prostacyclin is diminished. In this study the morphological appearance and time course for recovery of prostacyclin production after balloon dilatation have been investigated. Healthy rabbit aortas were analysed 1 h (n = 12), 1 week (n = 13) and 1 month (n = 13) after angioplasty. The production of prostacyclin, from dilated and non-dilated aortic segments, was recorded in a perfusion system. Prostacyclin was measured as its stable degradation product 6-keto-PGF1 alpha. Scanning electron microscopy and light microscopy were used to analyse the type of cells present at the luminal surfaces of the segments. When endothelial cells were found their degree of coverage was also estimated. One hour after balloon dilatation there was a lower production of prostacyclin from the angioplasty segments than from controls. Also, the response to added arachidonic acid (AA) was lower in the angioplasty segments. No endothelial cells were present in the angioplasty segments. After 1 week there was no difference in the basic production of prostacyclin but there was still a lower response from angioplasty segments to the addition of AA. The inner surfaces of the angioplasty segments were covered by three to five layers of smooth muscle cells (SMC). After 1 month, there was no difference in either the basic production or after the addition of AA between control and angioplasty segments. The angioplasty segments were covered with a multilayer of SMC. The control segments had an almost complete cover of endothelial cells at every time interval after angioplasty.(ABSTRACT TRUNCATED AT 250 WORDS)

Accumulation of cholesteryl ester in atherosclerotic lesions

This article reviews aspects of the molecular pathology of cholesteryl ester accumulation in atherosclerotic lesions. 1. Transcytosis of lipoproteins through a cultured endothelial monolayer. 2. Effects of platelets and PGI2 on intercellular transport of endothelial cells. 3. Transformation of macrophages to foam cells. 4. Cholesteryl ester deposition in the extracellular space of atherosclerotic lesions. The development and use of novel monoclonal antibodies recognizing atherosclerotic lesions and peroxidized lipoproteins prepared from then are also discussed.

Intercellular transport through a partially denuded arterial endothelial monolayer. Effect of platelets and PGI2

Fluorescein Dextran (FD) was shown to be transported at increased rates through partially denuded endothelial monolayer. Platelet binding to the partially denuded monolayer lowered transport rates to those comparable with intact endothelium. Inhibition of transport by platelet binding was not affected by the addition of isocarbacyclin (a stable derivative of PGI2). This result suggests that adherent platelets at the partial denudation site are sufficient to suppress transport of FD.

Arterial response to mechanical injury: balloon catheter de-endothelialization

Coronary angioplasty has been used clinically for over a decade. Its initial promise as an alternative to coronary bypass surgery has only partially been fulfilled because of the high rate of post-operative restenosis. A number of animal models have been devised to study this phenomenon and although none is entirely satisfactory, they have, together with recent advances in molecular biology provided an insight into the cellular mechanisms that may contribute to this complication. This knowledge may ultimately lead to a means of therapeutic intervention. This review summarises our present understanding of the pathology of post-angioplasty re-stenosis as revealed by studies using the balloon catheter de-endothelialization model, and discusses some of the intervention strategies that have been attempted.

Effect of PGI2 on platelet binding to partially denuded endothelial monolayer in vitro

We have developed a new model for the investigation of platelet interaction with injured vascular endothelium. This involves the quantitative detection of platelet binding to a partially denuded endothelial cell monolayer in vitro. Porcine arterial endothelial monolayer, cultured on collagen gel containing fibrinogen and fibronectin, was partially denuded and the binding of 51Cr-platelets was measured. A synergistic increase in platelet binding was observed in the presence of fibrinogen and fibronectin. A distinct aggregation of platelets along the edge of the denuded area of the endothelial monolayer was seen. Prostacyclin (PGI2) inhibited platelet aggregation, although adhesive platelets were still present at denuded sites.

Age-related decline in prostacyclin synthesis by human aortic endothelial cells. Qualitative and quantitative analysis

To investigate the functional alteration of human aortic endothelial cells with aging, prostacyclin synthesis was qualitatively and quantitatively examined. The endothelial cells of human aortas and umbilical veins or inferior vena cavae were immunohistochemically examined and found positive for prostacyclin, but the intensity of aortic endothelial cells from older subjects was low. In addition to the endothelial cells, smooth muscle cells in the thickened intima, not the media, of the aorta were also immunoreactive. Endothelial cells were successfully cultured from human aortas obtained from infants through aged subjects and were subdivided into three groups: young, middle, and old. Prostacyclin synthesis by endothelial cells from all types of blood vessels was extremely great at the primary culture, but decreased abruptly in the following subcultures. Among the aortic endothelial cells, the young group synthesized the largest amount of prostacyclin in a conventional culture condition, with synthesis progressively decreasing in the older groups. The in vitro prostacyclin biosynthesis was supported by the qualitative analysis on the tissue sections. These results indicate that prostacyclin synthesis of the aortic endothelial cells decreases with age, but intimal smooth muscle cells potentially have a back-up mechanism and substitute this synthesis to some extent. The decreased synthesis of prostacyclin with age may play an important role in the development and advancement of thrombosis and atherosclerosis.

Myointimal hyperplasia: pathogenesis and implications. 2. Animal injury models and mechanical factors

Arterial wall injury either by balloon catheter, drying, or scraping results in a denudation of endothelial cells (EC) and a subsequent proliferation of smooth-muscle cells (SMC). The degree of SMC proliferation appears to be dependent on the degree of initial injury and not to the loss of the overlying endothelium. Successful reendothelialization of denuded areas depends on the size of the denuded segment as well as SMC-EC interactions. Prolonged exposure of SMC to serum substances results in inhibition of EC regrowth, the production of prostacyclin by SMC, and the development of a thromboresistant surface. Heparin appears to inhibit SMC proliferation in vivo (as well as in vitro), an effect that is independent of platelet SMC interaction. EC-derived heparin in vivo may also result in inhibition of SMC proliferation. Platelets may play an important role in the early response to arterial injury and development of myointimal hyperplasia (MIH), but their long-term role appears to be minor. Antiplatelet agents have widely varying species-dependent effects on platelets and platelet-vessel wall interactions, but in specific circumstances they may inhibit MIH. The precise role of steroid drugs and immunosuppression on MIH in arterial injury models awaits further study. The role of lipoproteins in MIH is unclear; however, the inhibition of MIH by omega-3 fatty acids in vivo as well as their inhibition of platelet-derived growth factor production by EC in vitro implies a regulatory role. Acute hypertension results in a marked proliferation of EC and SMC in vivo and enhances the proliferative response to injury as well. Low wall shear stress, turbulence, and boundary layer separation all increase EC turnover, a likely influence on EC growth factor production. The compliance mismatch resulting from graft-artery anastomoses, injury, and endarterectomy results in locally increased cyclical stretch, which may predispose to SMC proliferation.

Mammary gland blood flow and plasma concentrations of 6-keto-prostaglandin F1 alpha in the goat

1. Mammary blood flow and concentrations of the stable metabolite of prostacyclin, 6-keto-prostaglandin F1 alpha, in mixed venous and mammary venous blood plasma have been measured in five lactating goats at various times during the day. 2. Natural variation in blood flow was not associated with any local release of 6-keto-prostaglandin F1 alpha into the mammary venous circulation.

Effect of short-term prostacyclin administration on restenosis after percutaneous transluminal coronary angioplasty

The effect of short-term prostacyclin (PGI2) administration on the incidence of restenosis after coronary angioplasty was studied in a prospective single-blind randomized trial of 286 patients. Of the 270 patients in whom dilation was successful, 134 received prostacyclin and 136 received placebo. Intracoronary prostacyclin was administered before and after dilation and then intravenously for 48 h. The control group received intracoronary placebo infusions before and after dilation. All patients received aspirin and dipyridamole before and after angioplasty, at least until follow-up angiography. Follow-up angiograms were obtained in 93% of patients in whom angioplasty was successful. Restenosis of one or more lesions was present in 34 patients (27%) who were given prostacyclin compared with 40 patients (32%) in the control group (p = NS). Acute vessel closure and ventricular tachyarrhythmias were more common in the control group than in the patients who received prostacyclin (acute vessel closure occurred in 14 [10.3%] of 136 versus 4 [3.0%] of 134, respectively, p less than 0.01; ventricular tachyarrhythmias occurred in 5 [3.4%] of 147 versus 0 of 139 respectively, p less than 0.05). Short-term administration of prostacyclin did not significantly lower the risk of restenosis after coronary angioplasty.

Endothelial control of vascular tone in large and small coronary arteries

The endothelium modulates coronary vascular tone by the release of endothelium-derived relaxing or contracting substances. The endothelium-derived relaxing factor has been identified as nitric oxide synthesized in endothelial cells from L-arginine. The endothelium can release other relaxing substances such as prostacyclin and a hyperpolarizing factor. Endothelin-1 is a potent vasoconstrictor peptide formed by endothelial cells, and is likely to be the physiologic antagonist of endothelium-derived relaxing factor. Other putative contracting factors include superoxide anions and products of arachidonic acid metabolism. Endothelium-derived relaxing factor is released spontaneously and in response to flow, platelet-derived products (that is, serotonin, thrombin and adenosine diphosphate) and certain autacoids (that is, acetylcholine, bradykinin, histamine, substance P, vasopressin, alpha-adrenergic agonists). A considerable heterogeneity of responses exists among vessels of different size from different anatomic origin and different species. Hypercholesterolemia, atherosclerosis, hypertension and myocardial ischemia or reperfusion, or both, impair endothelium-dependent relaxation. Under normal conditions, endothelium-derived relaxing factor appears to dominate the control of vascular tone of large and small coronary vessels, whereas in disease states, endothelium-derived contracting factors are released. Impairments of endothelial function may be important in the development of various forms of cardiovascular disease.

Influence of transluminal angioplasty on the prostanoid release from the arterial wall

Vasospasm and thrombosis complicate percutaneous transluminal angioplasty (PTA). To study if the release of the prostanoids PGI2 and TxA2 are affected by PTA, the following experiment was undertaken: In ten rabbits, the upper or lower half of the aorta was randomised either to transluminal angioplasty or control segment. After excision the segments were simultaneously but separately perfused ex vivo with Hank's balanced salt solution for five consecutive 15 min periods. Arachidonic acid was added to the perfusate for the last 15 min period. PGI2 and TxA2 were measured by radioimmunoassay in the perfusate as the stable degradation products 6-keto-PGF1 alpha and TxB2. After perfusion, the two aortic segments were prepared for scanning electron microscopy (SEM). Angioplasty decreased the basic release of PGI2 as well as the response to arachidonic acid. This is likely to be due to endothelial denudation as seen by SEM. The release of TxA2 from the vessel wall was very low and was not increased by dilatation. The influence of angioplasty on the prostanoid system may be of importance in the complications of vasospasm and thrombosis.

Prostacyclin and vascular function: implications for hypertension and atherosclerosis

Prostacyclin and endothelium-derived relaxing factor (or nitric oxide) are unstable mediators produced by the vascular endothelium, that are important for local regulation of platelet behavior and blood flow. This review focuses on the basic biochemistry and pharmacology of prostacyclin, its interactions with nitric oxide and nitrovasodilator drugs, and the implications of disturbances in this system for vascular disease, particularly hypertension and atherosclerosis. Prostacyclin and its stable analogs are also finding limited therapeutic applications in preservation of platelet function, pulmonary hypertension, and investigation into the cytoprotective and antiatherosclerotic properties is continuing.

Intrarenal mechanisms that regulate sodium excretion in relationship to changes in blood pressure

Because pressure-related natriuresis may be central to the regulatory role of the kidney on blood pressure, it is important to understand the relationship of humoral systems involved in the control of renal hemodynamics and tubular function. The preglomerular endothelial synthesis of prostaglandin I2 and endothelium-derived relaxing factor seem to modulate autoregulatory control by the afferent arterioles and the release of renin by the juxtaglomerular apparatus. The release of renin is followed by an increase in angiotensin II in the renal interstitium, which is responsible for adjusting the vascular tone of the efferent arterioles and vasa recta and for stimulating proximal tubular reabsorption of sodium. Variations in medullary circulation induced by angiotensin II could alter medullary interstitial pressure and the medullary production of prostaglandins E2 and I2 and, ultimately, could modulate sodium reabsorption in the medullary thick ascending limbs and the collecting ducts.

Kinin antagonist reverses converting enzyme inhibitor-stimulated vascular prostaglandin I2 synthesis

Treatment with a converting enzyme inhibitor has been shown to stimulate aortic prostaglandin I2 synthesis. We studied whether converting enzyme inhibitor-stimulated prostaglandin I2 synthesis might be mediated by kinins. Anesthetized male Sprague-Dawley rats were given a continuous 70-minute infusion of either saline or a kinin analogue antagonist, [DArg0-Hyp3-Thi5-DPhe7-Thi8]bradykinin, 8 micrograms/kg/min. After 10 minutes, rats were given an intravenous bolus of either vehicle or the converting enzyme inhibitor enalaprilat (30 micrograms/100 g body wt). After 70 minutes, aorta and renal cortical slices were harvested and incubated in vitro in buffer without drugs at pH 7.4, 37 degrees C for 60 minutes. The buffer was then sampled for measurement of 6-keto prostaglandin F1 alpha (an index of prostaglandin I2), prostaglandin E2, and renin release (angiotensin I generation) by radioimmunoassay. The aortic prostaglandin I2 from rats treated with converting enzyme inhibitor was significantly elevated (36.7 +/- 5.0 ng/mg dry wt/hr) compared with aorta from rats treated with either vehicle (25.6 +/- 2.2 ng/mg/hr), kinin antagonist (25.1 +/- 2.4 ng/mg/hr), or kinin antagonist plus converting enzyme inhibitor (23.0 +/- 2.0 ng/mg/hr), p less than 0.02. There were no differences in aortic prostaglandin E2, renin release, or prostaglandin E2 from renal cortical slices. Direct in vitro incubation of aorta with molar concentrations of converting enzyme inhibitor from 10(-9) to 10(-4) had no effect on prostaglandin I2. These results suggest that kinins may mediate the effect of converting enzyme inhibition on aortic prostaglandin I2 synthesis and thereby may account for part of the hemodynamic responses resulting from treatment using converting enzyme inhibitors.