Thromboxane synthase inhibition: implications for prostaglandin endoperoxide metabolism. II. Testing the 'redirection hypothesis' in an acute intravenous challenge model

Role of oxygen free radicals in respiratory distress induced by arachidonic acid in the rat

The purpose of our present study is the possible implication of oxygen free radicals in the respiratory distress induced in rats by intravenous administration of arachidonic acid (20 mg/kg). The respiratory frequency was measured and plasma TXB2 concentration was assayed by RIA from blood withdrawn 1 min after arachidonic acid administration. The substances studied were: SOD, catalase, mannitol, DMSO, BHT, imidazole. All the drugs, except imidazole, significantly protect the rats from the respiratory distress induced by arachidonic acid. SOD, catalase, BHT and imidazole inhibit whereas mannitol and DMSO increase the plasma levels of TXB2. We suggest that oxygen free radicals generated in the respiratory burst induced by arachidonic acid are mainly responsible for the consequent respiratory distress.

Preliminary observations of the acute effects of selective serum thromboxane inhibition and angiotensin converting enzyme inhibition on blood pressure and renal hemodynamics in hypertensive humans

CGS 13080, a selective thromboxane synthetase inhibitor, was given intravenously (0.6 mg/kg over 6 hours) to eight hypertensive (diastolic 95-115 mm Hg) euvolemic caucasian females on their customary salt intake (24 hour urine Na: 142.9 +/- 14.8 meq). No change occurred in blood pressure or glomerular filtration rate (GFR): 95.2 +/- 7.2, control versus 95.0 +/- 9.0, CGS 13080 (ml/min); or renal plasma flow (RPF): 363.2 +/- 34.2, control, versus 373.2 +/- 31.2, CGS 13080, (ml/min). Prostaglandin production was altered: platelet generation of thromboxane B2 83.3 +/- 10.9, control, versus 5.4 +/- 1.8, CGS 13080 (ng/hr) (P less than .001); urinary prostaglandin E (PGE) 249.0 +/- 56.3, control, versus 443.9 +/- 79.8, CGS 13080 (ng/6 hr) (P = .06); urinary 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) 188.6 +/- 23.4, control, versus 287.9 +/- 21.8, CGS 13080 (ng/6 hr) (P = .01); urinary thromboxane B2 54.8 +/- 12.9, control, versus 58.6 +/- 20.3 CGS 13080 (ng/6 hr) (P = NS). Serum levels of renin, angiotensin II and aldosterone were not altered by CGS 13080. Captopril when dosed to lower diastolic blood pressure 5-7 mm Hg did not significantly affect GFR, RPF or RVR. Nor did it affect platelet generation of thromboxane B2 or urine concentrations of PGE, 6-keto-PGF1 alpha or thromboxane B2. Captopril did increase renin levels 1.2 +/- 0.2, control, versus 2.9 +/- 1.1, captopril (ng/ml/hr) (P = NS), but did not statistically change angiotensin II, or aldosterone levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Testing the "redirection hypothesis" of prostaglandin metabolism in the kidney

Furosemide increases the synthesis of two major renal eicosanoids, prostacyclin (PGI2) and thromboxane A2 (TXA2), by stimulating the release of arachidonic acid which in turn is metabolized to PGG2/PGH2, then to PGI2 and TXA2. PGI2 may mediate, in part, the early increment in plasma renin activity (PRA) after furosemide. We hypothesized that thromboxane synthetase inhibition should direct prostaglandin endoperoxide metabolism toward PGI2, thereby enhancing the effects of furosemide on renin release. Furosemide (2.0 mg . kg-1 i.v.) was injected into Sprague-Dawley rats pretreated either with vehicle or with U-63,557A (a thromboxane synthetase inhibitor, 2 mg/kg-1 followed by 2 mg/kg-1 X hr-1). Urinary 6ketoPGF1 alpha and thromboxane B2 (TXB2), reflecting renal synthesis of PGI2 and TXA2, as well as PRA and serum TXB2, were measured. Serum TXB2 was reduced by 96% after U-63,557A. U-63,557A did not affect the basal PRA. Furosemide increased PRA in both vehicle and U63,557A treated rats. However, the PRA-increment at 10, 20 and 40 min following furosemide administration was greater in U-63,557A-treated rats than in vehicle-treated rats and urine 6ketoPGF1 alpha excretion rates were increased. These effects of thromboxane synthesis inhibition are consistent with a redirection of renal PG synthesis toward PGI2 and further suggest that such redirection can be physiologically relevant.