EFFECTS OF THE OESTROUS CYCLE AND EXOGENOUS OVARIAN STEROIDS ON METABOLISM OF β‐PHENYLETHYLAMINE IN RAT LUNG

Abstract

Metabolism of [14C]‐β‐phenylethylamine (PEN), a substrate for monoamine oxidase‐B (MAO‐B), was measured in lung homogenates and in perfused lungs during the 4 day oestrous cycle of the rat. Metabolism in vitro was high during met‐oestrus and di‐oestrus and low during pro‐oestrus and oestrus; this variation in activity correlated with changes in Vmax of the enzyme without changes in Km. PEN metabolism in lung homogenates was also altered by treatment of rats with 17β‐oestradiol but not by progesterone treatment. Metabolism of [14C]‐PEN in perfused lungs was the same during either pro‐oestrus or met‐oestrus. Uptake of [14C]‐PEN in perfused lung measured directly was also the same at these two stages. These results demonstrate that in lungs MAO‐B activity was affected by endogenous changes in steroid level but that such changes in enzymic activity were not reflected in the metabolic properties of whole lung.