Antibodies to 5,6-dihydroprostaglandin I2 trap endogenously produced prostaglandin I2 in the rat circulation.

Abstract Rabbit immunoglobulins raised against 5,6-dihydroprostaglandin I 2 which crossreact with prostaglandin I 2 were infused intravenously into Inactinanaesthetised male adult rats. Clearance of intravenously administered [ 3 H] prostaglandin I 2 from the blood, which is normally rapid ( t 1 2 approx. 45 s), was delayed strikingly in the presence of antibody ( t 1 2 approx. 60 min). The antibodies also sequestered the endogeneously synthesized prostaglandin I 2 and inhibited its metabolism. The rate of appearance of endogenous prostaglandin I 2 in the circulation of the rat was measured in the following way: arterial blood samples (0.5 ml) were withdrawn before, during and at various time intervals (up to 180 min) after infusion of antibodies had terminated; the prostaglandins were extracted from the blood with ethanol, and the extracts were assayed by radioimmunoassay (before and after separation by highpressure liquid chromatography) for the following prostaglandins: 6-keto-F 1α , E 2 , F 2α and 13,14-dihydro-15-keto-metabolites of E 2 and F 2α . Rapid and specific time-related increments of prostaglandin I 2 (detected serologically as 6-keto-F 1α ) were observed. At 180 min these increases ranged from 1500-to 2500-fold over preinfusion levels. No significant increases were observed in the other prostaglandins measured; nor were there increases in 6-keto-F 1α when saline or immunoglobulins from non-immune plasma were infused into rats. When measured by these procedures, no appreciable differences in 6-keto-F 1α production were found between Japanese normotensive and spontaneously hypertensive rats.