L.C. Lai

In vivo conversion of norethisterone to ethynyloestradiol in perimenopausal women

The extent to which norethisterone is converted to ethynyloestradiol is controversial. To investigate the conversion of norethisterone to ethynyloestradiol we have used a double isotope infusion technique to measure the conversion in vivo. The use of acids or bases was precluded to prevent possible artefactual formation of phenolic metabolites of norethisterone. Transfer constants for the conversion of norethisterone to ethynyloestradiol in two perimenopausal women were 2.26 and 2.34% as measured in blood and 2.27 and 0.38% in urine. Results from this study show that a small but significant proportion of norethisterone is converted to ethynyloestradiol in vivo.

Relationship between epidermal growth factor and dehydroepiandrosterone and its sulphate in breast cyst fluid.

Gross cystic breast disease is a common condition. Women with apocrine breast cysts may be at higher risk of breast cancer than women with cysts which are lined by flattened epithelium. Apocrine cysts have been shown to be associated with higher intracystic levels of dehydroepiandrosterone sulphate and intracystic sodium to potassium ratios of less than 3. In this study we measured the concentrations of epidermal growth factor, dehydroepiandrosterone and its sulphate in breast cyst fluid. The concentrations of all three analytes were significantly higher in cysts with intracystic Na+/K+ ratios of less than 3 than in cysts with electrolyte ratios of greater than or equal to 3 (P less than 0.001). The higher levels of EGF in cysts with low intracystic electrolyte ratios may provide an explanation of why women with apocrine cysts may be at greater risk of breast cancer. Positive correlations were obtained between concentrations of EGF and DHAS and between EGF and DHA, compatible with the view that intracystic EGF levels may be androgen-modulated. A positive correlation was also obtained between DHA and DHAS concentrations which supports the view that DHA in cyst fluid may be derived from the metabolism of DHAS in the breast cyst wall.

The effect of medroxyprogesterone acetate on aromatase and DNA polymerase α activities in breast tumours

The effect of treatment with the progestogen medroxyprogesterone acetate (MPA) on the peripheral conversion of androstenedione to oestrone and tumour aromatase activity has been examined in post-menopausal women with advanced breast cancer. In addition to being a potent progestational compound, MPA also possesses glucocorticoid properties and glucocorticoids have been shown to stimulate in vitro aromatase activity. While some evidence was obtained of an increase in aromatase activity in tumour tissue after treatment with MPA, peripheral conversion of androstenedione to oestrone was similar when measured before (2.12 +/- 0.67%) and after (1.89 +/- 0.16%) treatment. DNA polymerase alpha activity, measured as a marker of cellular proliferation, decreased from 331 +/- 145 to 156 +/- 93 pmol thymidine triphosphate (TTP)/mg protein per h (P less than 0.02) in tumour samples examined before and after treatment. It is concluded that treatment with high doses of MPA has no effect on the peripheral conversion of androstenedione to oestrone but results in a significant reduction in tumour DNA polymerase alpha activity.

Effect of breast cyst fluid on oestrogen 17-oxidoreductase activity in MCF-7 breast cancer cells

Breast cyst fluid (BCF) was found to stimulate oestrogen 17-oxidoreductase activity in the reductive direction, i.e., conversion of oestrone (E1) to oestradiol (E2), in MCF-7 breast cancer cells. Dialysis of BCF revealed that this property of BCF was present in both dialysed BCF and dialysate, implying that both high and low mol. wt. substances were responsible for stimulating E1 to E2 conversion. Gel filtration of dialysed BCF revealed that the high mol. wt. substances responsible for the stimulation of E1 to E2 conversion had mol. wts. of approximately 11 kD and 68 kD. This property of BCF would serve to increase the concentration of E2, a steroid which may play a role in mammary carcinogenesis.

The effects of androgens and cortisol on the in vivo metabolism of oestradiol

We have examined the effect of co-administration of dehydroepiandrosterone sulphate, 5-androstenediol or cortisol on the metabolic clearance rate of oestradiol (MCR-E2) and conversion of oestradiol to oestrone (CRE2E1). Previous studies have shown that these androgens influence the metabolism of oestradiol in vitro while cortisol alters the distribution of oestradiol in plasma. The MCR-E2 and CRE2E1 were measured after 2.5 and 5 h of [3H]oestradiol infusion with co-infusion of androgen or cortisol starting after 2.5 h of tracer infusion. For one subject who did not receive co-infusion of another steroid no significant change in MCR-E2 or CRE2E1 occurred over the 5-h period. For other subjects, however, the MCR-E2 decreased by 18 +/- 7% (mean +/- SD) while the CRE2E1 increased by 45 +/- 12%. It is possible that these results are due to: changes in the distribution of oestradiol in plasma; differences in the metabolism of oestradiol bound to albumin or SHBG, or an effect of androgens or cortisol on the uptake of [3H]oestradiol by the liver.

Analysis by DNA polymerase alpha activity of human breast tumour proliferation and the effect of endocrine therapy.

Cytosols of human breast tumours have been assayed for DNA dependent DNA polymerase alpha activity. DNA polymerase alpha activity in benign tumours was found to be significantly lower than in untreated malignant tumours. Biopsy samples removed surgically before and after endocrine therapy showed reduced DNA polymerase alpha activity in 6 out of 9 patients treated with 4-hydroxyandrostenedione, and in 6 out of 7 patients treated with MPA. DNA polymerase alpha activity in malignant breast tumours was higher in oestrogen receptor negative than oestrogen receptor positive tumours.

In vitro metabolism of testosterone by breast microcysts

Breast microcysts are considered to be a normal findings in the adult female breast without any increased risk of developing carcinomatous change. Breast cysts fluid contains steroid but not studies have been reported on the ability of breast microcysts to metabolise steroid hormones. It was, therefore, the aim of this study to identify the metabolites formed on incubation of radiolabelled testosterone with microcysts. In all instances dihydrotestosterone and androstenedione were formed. Oestrogens were not identified. Tis study, therefore, provides evidence for th presence of 5-alpha-reductase and 17-oxidoreductase enzyme systems in breast microcysts.