Inactivation of prostaglandin E2 by rat isolated lung during the oestrous cycle

The metabolism of prostaglandin E2 (PGE2) in lungs from female rats was measured during the stages of the oestrous cycle. In isolated lungs perfused through the pulmonary circulation, only 7-20% of PGE2 escaped metabolism, as measured by bioassay and radioimmunoassay. Within these limits, survival was highest at pro-oestrus compared with metoestrus and dioestrus. Uptake of PGE2 from the pulmonary vasculature, assessed by measuring the efflux of radioactivity derived from [14C]PGE2 injected into the pulmonary circulation of the isolated lung, did not show cycle-related variations. Assay of [14C]PGE2 metabolism by tissue homogenates prepared from lungs taken at different stages of the oestrous cycle showed a significant decrease in enzyme activity at pro-oestrus compared with dioestrus. It is concluded that PGE2 metabolism in isolated rat lung is affected by the oestrous cycle and that the increased PGE2 survival at pro-oestrus may be more readily explained by changes in enzyme activity than by changes in uptake of substrate.