Simultaneous measurement of two major prostacyclin metabolites in urine

We describe a combined HPLC-RIA technique to measure both major metabolites of prostacyclin (PGI2): 6-keto PGF1 alpha and 2,3-dinor-6 keto PGF1 alpha. The measurement of the former, which originates from renal blood vessels, and the latter, from systemic vessels and the liver, may provide a better overall evaluation of production than measurement of one metabolite. An aliquot of acidified urine with added 3H-labeled metabolites is adsorbed and then eluted from a C18 Bond-Elut column. The sample is then passed through an HPLC system by use of an isocratic solvent combination that separates the two metabolites from known prostaglandins. The purified metabolites are then quantified by RIA. Using a logit-log10 transform, one can measure between 12 and 250 pg of either metabolite, with high accuracy and precision (CVs of 12% for a low concentration and 7% for a high concentration). Reference values for apparently healthy subjects were, respectively, 107 (SD 45) and 171 (SD 69) ng/g creatinine for 6-keto PGF1 alpha and the dinor metabolite in men (n = 18) and 45 (SD 22) and 141 (SD 28) ng/g creatinine, respectively, in women (n = 15). Indomethacin in standard doses reduced both metabolite values by 50%. Intravenous administration of angiotensin II (5 ng/kg of body wt per minute) did not alter excretion rates, but equipressor doses of norepinephrine (0.1 microgram/kg per minute) increased the production of both metabolites (6-keto greater than dinor).