Metabolites of PGF2 alpha in blood plasma and urine as parameters of PGF2 alpha release in cattle.

The metabolism of PGF in cattle results initially in the formation of 15-keto-13,14-dihydro-PGF (15-ketodihydro-PGF) and later the 11-ketotetranor PGF metabolites. Both types of metabolites appear in the peripheral circulation and finally the 11-ketotetranor PGF metabolites are found in large quantities in the urine in a species-related pattern. Several approaches can be made to the quantitative analysis of PGF release during reproductive studies. First, assay of the 15-ketodihydro-PGF metabolite in the peripheral circulation; second, analysis of the longer-lived 11-ketotetranor PGF metabolites in the peripheral circulation; and finally analysis of the latter metabolites in the urine. The antibodies used in radioimmunoassays of both types of metabolites of PGF were found to be specific and the results agree well with those obtained earlier by mass spectrometric analysis. The assay of 11-ketotetranor PGF metabolites was used to study the excretion of urinary metabolites in the cow after i.v. infusion of PGF and also during the normal estrous cycle and early pregnancy. These studies suggest that 11-ketotetranor PGF metabolites in cow urine serve as a good parameter of PGF release, especially for long–term studies, but when a precise pattern of PGF release is required, measurement of 15-ketodihydro-PGF levels in frequently collected plasma samples is preferable.