1 Five patients have been studied to determine the contribution of the gut wall to the pre-systemic metabolism of ethinyloestradiol. All patients had a catheter inserted into their hepatic portal vein as part of their surgical management. 2 After an oral dose of 50 micrograms (65 microCi) ethinyloestradiol, blood samples were taken from the hepatic portal vein and from a peripheral vein at intervals for 1 h. 3 In each patient the concentration of conjugated ethinyloestradiol in the portal vein was considerably higher than in the peripheral vein. 4 Although a number of assumptions have been made, calculations showed that the gut wall appeared to be twice as effective as the liver in conjugating ethinyloestradiol on the first pass. 5 In two patients there was no evidence of major uptake or metabolism of ethinyloestradiol in the lung.
PIP: 5 patients aged 58-70 were studied to determine the quantification of the gut wall metabolism of ethinylestradiol by sampling simultaneously from the portal vein and from a peripheral vein after an oral dose of 50 mcg of tritated ethinylestradiol. Higher levels of conjugated metabolites were demonstrated in the portal vein than in the systemic vein; the fraction of conjugated ethinylestradiol in the gut wall was 0.44, while the conjugated fraction in the liver was only 0.25. It appeared that the gut wall was almost twice as effective as the liver in conjugating ethinylestradiol. Studies of conjugate concentrations in th lung showed that the lung is not a major organ of uptake for ethinylestradiol. Further studies are necessary.