Isolation of prostacyclin from whole blood

Stability and preservation of a new formulation of epoprostenol sodium for treatment of pulmonary arterial hypertension

Background

The aim of this study was to evaluate the stability and microbiological properties of a formulation of epoprostenol sodium with L-arginine and sucrose excipients (epoprostenol AS).

Methods

The stability of the reconstituted solutions after storage at 5°C and 25°C, diluted solutions (3000–60,000 ng/mL) at controlled room temperature, and diluted solutions (3000–60,000 ng/mL) stored at 5°C and then at room temperature were evaluated. Solutions were prepared using sterile water for injection or sterile saline (sodium chloride 0.9%) for injection. Shelf-life was assessed by determining potency over time relative to initial potency. In this context, potency is synonymous with content. The antimicrobial activity of reconstituted (100,000 ng/mL for 0.5 mg vial, 300,000 ng/mL for 1.5 mg vial) and diluted (3000 ng/mL) epoprostenol AS was measured using an antimicrobial effectiveness test after inoculation with six species of bacteria, yeast, and mold.

Results

Reconstituted epoprostenol AS was stable for up to one day’s storage at 25°C or 7 days’ storage at 5°C. Epoprostenol AS was stable for up to 72 hours when diluted, depending on temperature and concentration. The maximum shelf-life of the diluted solution if the reconstituted solution had been stored for up to one day at room temperature or up to 7 days at 5°C, was between 24 and 72 hours, depending on concentration. Following storage of diluted solutions at 5°C for up to 8 days, maximum shelf-life was between one and 2 days, depending on temperature and concentration. Potency was not dependent on diluents. Preservative testing confirmed no microbial growth for any of six organisms tested for at least 14 days at 5°C or 25°C for the reconstituted solution and for at least 16 days at 5°C followed by one day at 25°C for the diluted solutions.

Conclusion

Epoprostenol AS has favorable thermal stability and does not support the growth of any micro-organism tested for up to 17 days. This extended stability under ambient conditions has the potential to improve convenience further for patients.

Stability and microbiological properties of a new formulation of epoprostenol sodium when reconstituted and diluted

Purpose

Epoprostenol, used for the treatment of pulmonary arterial hypertension (PAH), has a number of limitations related to its short half-life in aqueous solution. The aim of this study was to evaluate the stability and microbiological properties of a new formulation, namely epoprostenol sodium with arginine and mannitol excipients (epoprostenol AM; Veletri^®; Actelion Pharmaceuticals Ltd, Allschwil, Switzerland).

Methods

Stability and microbiological properties of epoprostenol AM were investigated at 5°C, 25°C, and 30°C over a range of concentrations (3000–30,000 ng/mL) when reconstituted and immediately diluted with sterile water for injection (SWI) or sterile saline (sodium chloride 0.9%) for injection (SSI). Stability (change in potency over time) for up to 72 hours at 25°C and 30°C was measured immediately following dilution and after storage at 5°C. Shelf-life was assessed by determining the maintenance of potency over time relative to initial potency. For microbiological testing, diluted samples of epoprostenol AM were inoculated with a range of bacteria, yeasts, and molds for up to 14 days at 5°C or 4 days at 25°C.

Results

Epoprostenol AM reconstituted and immediately diluted to the required concentration with SWI or SSI was stable for up to 3 days at 25°C and up to 7 days at 5°C depending on the concentration. None of the diluted epoprostenol AM solutions supported microbial growth for any of the six organisms tested for up to 14 days.

Conclusions

Epoprostenol AM has improved thermal stability and does not support the growth of any microorganism tested for up to 14 days. This extended stability under ambient conditions has the potential to improve convenience for patients.

Prostaglandin E2 levels in blood plasma and in crevicular fluid of advanced periodontitis patients before and after surgical therapy

AIM

The aim of the study was to determine PGE2 levels in venous blood plasma (VBP), gingival blood plasma (GBP) and gingival crevicular fluid (GCF) in advanced periodontal patients before and after 6 months surgical treatment.

PATIENTS AND METHODS

There were 12 patients aged 28-45 years and seven healthy subjects as controls included into the study. Clinical parameters such as PLI, GI, BI, PD, AL and bone height % from radiographs were recorded before and after treatment. PGE2 levels were determined by radioimmunoassay (125 I RIA Kit, NEN(R)).

RESULTS

Before treatment the mean VBP, GBP and GCF PGE2 levels in periodontal patients were higher than healthy controls (P < 0.001, Student's t-test). Six months after treatment the mean levels of PGE2 in VBP, GBP and GCF were significantly reduced in patients with improvement of clinical and roentgenological parameters (P < 0.001, Student's t-test).

CONCLUSIONS

It can be concluded that PGE2 is involved in the pathogenesis of periodontal disease. The inflamed periodontal tissues may produce significant amount of PGE2 and the degree of inflammation might be determined by the ratios of PGE2. The lower levels of PGE2 in blood plasma and in gingival crevicular fluid after treatment are signs of improvement of periodontal disease.

The effects of thrombocytopenia on vessel stasis and macromolecular leakage after photodynamic therapy using photofrin

Several studies have reported thrombus formation and/or the release of specific vasoactive eicosanoids, suggesting that platelet activation or damage after photodynamic therapy (PDT) may contribute to blood flow stasis. The role of circulating platelets on blood flow stasis and vascular leakage of macromolecules during and after PDT was assessed in an intravital animal model. Sprague-Dawley rats bearing chondrosarcoma on the right hind limb were injected intravenously (i.v.) with 25 mg/kg Photofrin 24 h before light treatment of 135 J/cm2 at 630 nm. Thrombocytopenia was induced in animals by administration of 3.75 mg/kg of rabbit anti-rat platelet antibody i.v. 30 min before the initiation of the light treatment. This regimen reduced circulating platelet levels from 300,000/mm3 to 20,000/mm3. Reductions in the luminal diameter of the microvasculature in normal muscle and tumor were observed in control animals given Photofrin and light. Venule leakage of macromolecules was noted shortly after the start of light treatment and continued throughout the period of observation. Animals made thrombocytopenic showed none of these changes after PDT in either normal tissues or tumor. The lack of vessel response correlated with the absence of thromboxane release in blood during PDT. These data suggest that platelets and eicosanoid release are necessary for vessel constriction and blood flow stasis after PDT using Photofrin.

Pathogenic role of thromboxane A2 in immediate food hypersensitivity reactions in children

BACKGROUND

Food hypersensitivity, from the standpoint of pathogenesis as well as clinical management, remains controversial. During the food allergen-induced immediate hypersensitivity reaction, various chemical mediators are released.

OBJECTIVE

The purpose of our study was to determine whether thromboxane A2 participates in food antigen-induced responses in children with food hypersensitivity.

METHODS

Nine open food challenges were performed in nine patients with suspected food hypersensitivity. Plasma thromboxane B2 and histamine levels were measured during a 24-hour period following the challenge.

RESULTS

All the patients demonstrated immediate reactions after food challenge. The mean plasma thromboxane B2 level (a marker of thromboxane A2 activity) rose significantly at two hours and three hours after the challenge. Simultaneously, the mean plasma histamine level rose significantly at two hours and three hours after the challenge.

CONCLUSIONS

The results suggest that thromboxane A2 may play a pathogenic role in part in the immediate reaction after food challenge and that thromboxane A2 is probably released from a common cellular source (eg, mast cell) with histamine and/or by a common mechanism (eg, IgE-dependent platelet activation).

The effects of thromboxane inhibitors on the microvascular and tumor response to photodynamic therapy

Vascular stasis and tissue ischemia are known to cause tumor cell death in several experimental models after photodynamic therapy (PDT); however, the mechanisms leading to this damage remain unclear. Because previous studies indicated that thromboxane release is implicated in vessel damage, we further examined the role of thromboxane in PDT. Rats bearing chondrosarcoma were injected with 25 mg/kg Photofrin (intravenously) 24 h before treatment. Light (135 J/cm2, 630 nm) was delivered to the tumor area after injection of one of the following inhibitors: (1) R68070: a thromboxane synthetase inhibitor; (2) SQ-29548: a thromboxane receptor antagonist; and (3) Flunarizine: an inhibitor of platelet shape change. Systemic thromboxane levels were determined. Vessel constriction and leakage were evaluated by intravital microscopy. Tumor response was assessed after treatment. Thromboxane levels were decreased more than 50% with SQ-29548 as compared to controls. Thromboxane levels in animals given R68070 and Flunarizine remained at baseline levels. SQ-29548 and R68070 reduced vessel constriction compared to controls, while Flunarizine totally prevented vessel constriction. R68070 and SQ-29548 inhibited vessel permeability compared to PDT controls; Flunarizine did not. Animals given these inhibitors showed markedly reduced tumor cure. These results indicate that the release of thromboxane is linked to the vascular response in PDT.

The effects of photodynamic therapy using differently substituted zinc phthalocyanines on vessel constriction, vessel leakage and tumor response

The effects of four different zinc phthalocyanines were studied during and after photodynamic therapy (PDT). Measurements of vessel constriction, vessel leakage, tumor interstitial pressure, eicosanoid release, and tumor response of chondrosarcoma were made in Sprague-Dawley rats. Animals were injected intravenously with 1 mumol/kg of mono-, di-, or tetrasulfonated zinc phthalocyanine, or 1 mumol/kg of a zinc phthalocyanine substituted with four tertiary butyl groups. Tissues were exposed to 400 J/cm2 670 nm light 24 h after photosensitizer injection. An additional group of animals was given indomethacin before treatment. The use of the monosulfonated and tertiary butyl substituted zinc phthalocyanines in PDT caused the release of specific eicosanoids, caused vessel constriction, and induced venule leakage and increases in tumor interstitial pressure. Tumor cures of 27% and 7% were observed. Photodynamic therapy using the disulfonated zinc phthalocyanine did not induce vessel constriction or the release of eicosanoids, however, tumor cure was 43%. The use of the tetrasulfonated zinc phthalocyanine caused intermediate effects between the mono- and disulfonated compounds. The administration of indomethacin to animals completely inhibited the effects of PDT using the monosulfonated compound but had minimal effects on treatment using the disulfonated compound. This suggests that the monosulfonated and disulfonated compounds act by different mechanisms of destruction.

E and F alpha series prostaglandins in developing muscles

Prostaglandins are known to affect myoblast proliferation and fusion in vitro and are putative regulators of in vivo myogenesis. The levels of E and F alpha series prostaglandins in the thigh muscles of chicken embryos were measured by radioimmunoassays and correlated with indicators of muscle development. Just prior to the onset of secondary myogenesis, the amounts of PGE1, PGE2 and PGF1 alpha plus PGF2 alpha per mg of protein were high. In temporal association with myotube formation, the amount of PGE1 and PGE2 per mg of protein decreased. PGF alpha levels also fell, but at a slower rate than observed with the E series prostaglandins. The decreases in the amounts of prostaglandins per mg protein appeared to be due to a decline in the total amount of prostaglandin within each muscle. These observations are consistent with prostaglandins being one of the factors that controls in vivo muscle formation.

Plasma 11-dehydrothromboxane B2: a reliable indicator of platelet hyperfunction in patients with ischemic stroke

The plasma level of 11-dehydrothromboxane B2 (11-dehydroTXB2) is free from artifactual increase during blood sampling, and it can be reliable indicator of TXA2 production in vivo. We have estimated plasma 11-dehydroTXB2 in patients with ischemic stroke. Subjects studied were 29 patients with cerebral thrombosis (62 +/- 9 years old) and 41 healthy controls (61 +/- 7 years old). Plasma 11-dehydroTXB2 and TXB2 were determined by radioimmunoassay. Plasma 11-dehydroTXB2 levels in patients and controls were 5.4 +/- 2.5 and 1.8 +/- 0.9 pg ml, respectively, and the difference was significant (p less than 0.001). Plasma TXB2 also was higher in patients than in controls: 401 +/- 61 vs 311 +/- 51 pg/ml (p less than 0.05). However, the 11-dehydroTXB2 was found to be a more effective parameter to distinguish between stroke patients and controls. Estimation of plasma 11-dehydroTXB2 levels is a reliable method to detect platelet hyperfunction in stroke patients.

Effect of a continuously applied compressive pressure on mouse osteoblast-like cells (MC3T3-E1) in vitro

Bone metabolism is often affected by a variety of mechanical forces, but the cytological basis of their action is not known. In this study, we examined the effect of a continuously applied compressive pressure (CCP) on the growth and differentiation of clonal mouse osteoblast-like cells (MC3T3-E1) cultured in a specifically devised culture chamber. The gas phase of the chamber was maintained at a pressure of 2 atmospheres (atm) above ambient (3 atm total, 3.1 kg/cm2; 3.0 x 10(5) Pa) by continuously infusing a compressed mixed gas (O2: N2:CO2 = 7.0%:91.3%:1.7%). The pO2, pCO2, and pH in the culture medium at 37 degrees C under 3 atm were maintained at the same levels as those under 1 atm. MC3T3-E1 cells were cultured in alpha-minimal essential medium containing 10% fetal bovine serum under either 3 atm in the CCP culture chamber or 1 atm in an ordinary CO2 incubator. Alkaline phosphatase activity, a marker of osteoblasts, was greatly suppressed by the CCP treatment. The inhibition of alkaline phosphatase activity was rapidly restored when the cells were transferred to an ordinary CO2 incubator under 1 atm, indicating that the inhibition of alkaline phosphatase activity by CCP is reversible. Cell growth was not altered under CCP. The CCP treatment greatly increased the production and secretion of prostaglandin E2 (PGE2). Adding either conditioned medium from the CCP culture or exogenous PGE2 to the control culture under 1 atm suppressed alkaline phosphatase activity dose-dependently. The CCP treatment also suppressed collagen synthesis and calcification. These results suggest that CCP causes the cells to produce and secrete PGE2, which, in turn, inhibits differentiation of osteoblasts and the concomitant calcification.

Effects of chronic fetal hyperinsulinemia on plasma arachidonic acid and prostaglandin concentrations

In adult diabetic subjects and infants of diabetic mothers, hyperglycemia has been associated with increased intravascular thromboxane and decreased prostacyclin production. Because of the association between states of altered insulin concentration and prostaglandin metabolism, we hypothesized that chronic experimentally induced fetal hyperinsulinemia results in perturbations in fetal arachidonic acid and prostaglandin metabolism. Arachidonic acid, thromboxane B2 (the stable breakdown product of thromboxane A2), and 6-keto-prostaglandin F1 alpha (the stable breakdown product of prostacyclin) were determined in the arterial blood of chronically catheterized fetal sheep after 9 to 12 days of continuous insulin (15 U.day-1, n = 7) or placebo (n = 5) infusion. Fetal insulin infusion resulted in fetal hypoglycemia and a reduction in fetal arterial plasma arachidonic acid concentration (p less than 0.01). In addition, the concentration of thromboxane B2 relative to 6-keto-prostaglandin F1 alpha was significantly reduced in the insulin-treated group compared with the placebo-treated group (p less than 0.03). We conclude that fetal hyperinsulinemia in sheep produces perturbations in prostaglandin metabolism with reductions in the plasma arachidonic acid concentration and in the plasma concentration of thromboxane A2 relative to prostacyclin. The hyperinsulinemic-hypoglycemic state in the fetus influences the relative proportion of the vasoconstricting to the vasodilating prostaglandins, thereby potentially modulating fetal vasomotor tone.

Effect of emulsions of medium and long chain triglyceride on human adipose tissue prostaglandin production in vitro

Preliminary in vitro studies have been performed to assess the effect of experimental lipid emulsions of varying fatty acid composition on human adipose tissue metabolism. Subcutaneous human adipose tissue was obtained during elective surgery and placed in tissue culture. Physical mixtures of long chain triglyceride (LCT) and/or medium chain triglyceride (MCT) were added to the tissue culture medium so that the final concentration was 400 mg/dl. After a 3-day incubation period the tissue was harvested, placed in buffer and used to determine in vitro production of the prostaglandins prostacyclin I2 (measured as its stable endproduct 6-keto PGF1 alpha), thromboxane A2 (measured as TXB2), and prostaglandin E2. Measurements of the fatty acid profile found in the neutral- and phospholipid fraction of the adipose tissue and fat cell size were also made. The results demonstrate that samples incubated in 100% MCT had the most significant increase in prostaglandin production whereas those incubated in 100% LCT had the most significant decrease in activity of the three prostaglandins assayed, when compared to controls. The addition of LCT to MCT caused a dose-related decrease in adipose tissue prostaglandin production. There were no significant changes in the profile of fatty acids found in the neutral- or phospholipid fraction of adipose tissue. The results indicate that the relative level of MCT/LCT incubated with human adipose tissue has a significant effect on prostaglandin production.

Dietary biotin effects on polyunsaturated fatty acids in chick tissue lipids and prostaglandin E2 levels in freeze-clamped hearts

Chicks were fed a purified diet with 0, 100, 200, 300, 400, or 500 micrograms/kg diet of added biotin to determine the effects of biotin deficiency on polyunsaturated fatty acids in tissue lipids. Body weight was reduced by biotin deficiency and liver and heart biotin levels varied with the biotin in the diet. Fatty acids in liver and lung from biotin-deficient chicks at 15 days contained elevated (P less than .03) 18:3 omega 3 and 18:2 omega 6 but prostaglandin precursors 20:3 omega 6 and 20:4 omega 6 were reduced (P less than .03) in liver lipids. Heart tissues from 15-day-old chicks fed the biotin-deficient diet were low (P less than .03) in 20:3 omega 6. Feeding acetylsalicylic acid in diets containing added biotin (0, 100, 400, and 500 micrograms/kg) did not significantly alter fatty acid levels in chick tissue lipids but significantly reduced plasma prostaglandin E2 (PGE2). Biotin deficiency reduced heart PGE2 levels in 22-day-old chicks. An 8-h fast reduced (P less than .04) 20:4 omega 6 in chick heart total fatty acids.

Augmentation of endotoxin fever by recombinant human beta interferon in rabbits

Nonpyrogenic amounts of endotoxin (0.1 to 1 ng/kg), hardly detectable by conventional Limulus amoebocyte lysate tests, could produce a fever of around 1 degree C when injected with a nonpyrogenic dose (6 X 10(5) U/kg) of recombinant human beta interferon (IFN-beta) in rabbits. Release of endogenous IFN and tumor necrosis factor by endotoxin was also dramatically increased by recombinant human IFN-beta, and their levels in the blood were closely correlated with the increase of body temperature. These data suggest, if the synergism between IFN and endotoxin also operates in the homologous system (human IFN-human cells), that contaminating endotoxin in IFNs, even if not detectable by Limulus amoebocyte lysate test, can contribute to IFN fever to a considerable extent in humans.

Increased production of tumor necrosis factor and prostaglandin E2 by monocytes in cancer patients and its unique modulation by their plasma

We investigated the role of monocytes in the production of tumor necrosis factor (TNF) and prostaglandin E2 (PGE2) in 77 cancer patients with malignancies of the digestive tract, using 30 normal individuals and 18 noncancer patients as controls. Monocytes were incubated with lipopolysaccharide for 20 h, and TNF production and PGE2 production were analyzed by bioassays. Elevated levels of TNF (greater than 512 U/ml) and PGE2 (greater than 8 ng/ml) production were demonstrated in many cancer patients when these factors were induced in the medium with 10% fetal bovine serum. The elevated level of TNF was seen to be restricted for the most part to patients with malignancies. Thus, 51 out of 59 cancer patients (86%), consisting of 44 primary cancer patients and 15 recurrent cancer patients, showed an increased level of TNF. In contrast, almost all of 18 postoperative cancer patients showed TNF levels comparable to those of normal individuals. Furthermore, 16 primary cancer patients were also demonstrated to have reduced levels of TNF production by monocytes after curative operation. When 10% cancer-patient plasma was added to the induction culture, TNF production by monocytes was drastically suppressed in the cancer patients. Interestingly, the same addition of plasma induced a prominent enhancement of PGE2 production in the cancer patients. The plasma of noncancer patients did not modulate production of these factors. No TNF activity was found in the plasma of cancer patients, but such plasma did contain an increased level of PGE2 (100-300 pg/ml). Although PGE2 (greater than 2 ng/ml) was able to suppress TNF production by monocytes, the addition of 10% plasma PGE2 was not enough to induce suppression. An unknown factor(s) in the plasma of cancer patients may uniquely modulate the elevated TNF and PGE2 production in these patients.

Stability of prostacyclin in human and rabbit whole blood and plasma

The stability of prostacyclin (PGI2) in whole blood and plasma was studied in vitro by measuring the disappearance rate of labeled prostacyclin during a 37 degrees C incubation. Prostacyclin was assayed using a quantitative chromatographic method. The half-life of PGI2 was 6.3 +/- 0.8 minutes (mean +/- s.d., n = 6) in citrated human whole blood, significantly shorter (p less than 0.001) than the 10.7 +/- 2.3 minute half-life in citrated human plasma (n = 7). Prior freezing and thawing of plasma did not affect the rate of PGI2 hydrolysis. These values, including the prolonged half-life in plasma, were similar in the blood (5.4 +/- 1.8 min, n = 7) and plasma (9.0 +/- 1.9 min, n = 14) of diabetic patients. In plasma samples from patients with thrombotic thrombocytopenic purpura, the half-life of prostacyclin (4.9 +/- 1.0 min, n = 4) was significantly shortened (p less than 0.001) compared to that in plasma from normal volunteers. The stability of prostacyclin in rabbit blood and plasma was also quantified. The PGI2 half-life in citrated rabbit plasma (10.8 +/- 1.1 min, n = 3) was similar to that in citrated human plasma from control subjects. In contrast to the findings in human blood, the half-life of PGI2 in citrated rabbit whole blood (11.7 +/- 3.3 min, n = 4) was not different from the rabbit plasma value. Substitution of EDTA for citrate did not affect the half-life in rabbit blood or plasma.

Modification of focal cerebral ischemia by prostacyclin and indomethacin

✓ The object of this investigation was to study the effects of prostacyclin (PGI2), with and without indomethacin, upon the evolution of cerebral infarction in the cat. Thirty-five fasted adult cats, lightly anesthetized with nitrous oxide, underwent right middle cerebral artery (MCA) occlusion. Eleven cats received an intracarotid infusion of 10 mg/ml PGI2 in buffered saline, pH 10.5, at a rate of 0.01 ml/kg/min (100 ng/kg/min), 10 cats received the same infusion plus a single dose of intravenous indomethacin (4 mg/kg) in buffered saline, and 11 cats received intracarotid buffered saline, pH 10.5, at a rate of 0.01 ml/kg/min, without therapeutic agents. Treatment with PGI2 was started upon MCA occlusion and continued for 6 hours, whereas indomethacin was given immediately prior to occlusion. Thirty minutes before perfusion, the animals were given fluorescein and Evans blue by intravenous injection. The cats were perfusion-fixed in vivo with carbon and buffered formalin 6 hours after MCA occlusion. Another five cats received tritium-labeled PGI2, and peripheral venous samples were collected and assayed for PGI2 and its alpha-keto metabolite. Mean arterial pressure was stable in treated animals during 6 hours of MCA occlusion, while untreated cats had significant (α = 0.05) progressive hypertension during that period. The regional cerebral blood flow (rCBF), measured by the intracarotid xenon-133 clearance method, decreased markedly in all animals immediately upon MCA occlusion. Untreated animals had a significant progressive improvement in rCBF during the occlusion period (α = 0.005), while treated animals had no such improvement. Quantitative electroencephalographic changes, gross edema, areas of fluorescein extravasation, and microscopic morphology (edema and infarct size) were not significantly different in the three groups. Prostacyclin appeared to reduce the extravasation of Evans blue dye. Systemic PGI2 levels were significant despite intracarotid administration. The authors conclude that 1) intracarotid PGI2 has a protective effect against the breakdown of the blood-brain barrier to protein-bound dyes seen in ischemic edema; 2) the systemic hemodynamic influence of PGI2, in the presence of impaired autoregulation, may compromise rCBF in the ischemic zone and offset any direct beneficial effects; and 3) indomethacin fails to modify the effects of PGI2.

Treatment of acute focal cerebral ischemia with prostacyclin

The object of this investigation was to study the effects of prostacyclin (PGI2) upon the evolution of acute focal cerebral ischemia in the cat. Twenty-five fasted adult cats, lightly anesthetized with nitrous oxide, underwent right middle cerebral artery (MCA) occlusion. Eleven cats received an intracarotid infusion of PGI2 in buffered saline pH 10.5 (100 ng/kg/min at 0.01 ml/kg/min), and 11 cats received intracarotid buffered saline pH 10.5 (0.01 ml/kg/min) without therapeutic agents. Treatment with PGI2 was started upon MCA occlusion and continued for 6 hours. Thirty minutes prior to perfusion, the animals were given fluorescein and Evans blue by intravenous injection. The cats were perfused-fixed in vivo with carbon and buffered formalin 6 hours after MCA occlusion. Another 3 cats received tritium labeled intracarotid PGI2, and peripheral venous samples were collected and assayed for PGI2 plasma levels. Mean arterial pressure was stable in PGI2 treated animals during 6 hours of MCA occlusion, while untreated cats had significant progressive hypertension during that period. The rCBF (measured by the intracarotid 133Xe method) decreased markedly in all animals immediately upon MCA occlusion. However, untreated animals had a significant progressive improvement in rCBF during the occlusion period, while PGI2 treated animals had no such improvement. Quantitative EEG changes, gross edema, areas of fluorescein extravasation, patterns of carbon perfusion, and infarct size were not significantly different in the two groups. While most untreated animals had marked Evans blue extravasation after 6 hours of MCA occlusion, most PGI2 treated animals had no such extravasation, indicating some protection of the blood-brain barrier in these animals.