Human forearm and kidney conversion of arachidonic acid to prostaglandins

The capacity of the human forearm and kidney to synthetize different prostaglandins (PGs) was studied, together with the quantitative relationship between the various PGs formed in these organs. 14C-labelled arachidonic acid (14C-AA) was infused in healthy male volunteers at a constant rate into the brachial or the renal artery, with simultaneous sampling of regional venous blood. The venous plasma content of 14C-PGs was extracted, separated with thin-layer chromatography (TLC) and quantified using fractionated liquid scintillation spectrometry. Most of the 14C-AA infused was metabolized and radiopeaks parallel to unlabelled standards of PGD2, PGE2, PGF2 alpha, 6-keto-PGF1 alpha and 13,14-dihydro-15-keto-PGE2 (Me) were obtained. The chromatograms of both the forearm and the kidney plasma contained all the peaks described, but the relative distribution of the 14C-PGs differed between the two tissues. In the cubital venous plasma, the main PG (apart from Me) was 6-keto-PGF1 alpha, indicating a considerable synthesis of PGI2 in the forearm. In the renal venous plasma, on the other hand, PGD2 accounted for the largest part of the authentic 14C-PGs found. Besides the tissue differences, large inter-individual variations were observed. The results demonstrate the existence of both a considerable tissue specificity and an appreciable inter-individual variation in the local conversion of AA to PGs in man.