The effect of oral contraceptive steroids on bile secretion and bilirubin Tm in rats.

1. The effect of oestrogens and progestogens and their 17alpha-ethinyl derivatives on bile flow, maximum rate of bilirubin secretion, serum and liver bilirubin has been studied.2. Both 17alpha-ethinyl substituted oestrogens and progestogens greatly reduced the basal bile flow. The parent compounds, oestradiol-17beta and 19-nortestosterone had little or no effect.3. A much larger dose of progestogens (40 mg/kg) than oestrogens (5 mg/kg) was needed.4. Between 12 and 48 h were required for 17alpha-ethinyloestradiol to produce the effect.5. Bilirubin maximum secretion rate (Tm) was little affected, the only significant reduction being produced by the 3-methyl ether of 17alpha-ethinyloestradiol (mestranol).6. Rises in serum conjugated bilirubin following infusion of bilirubin were produced by 17alpha-ethinyloestradiol and mestranol but not by the progestogens.