Human epidermal growth factor (EGF) concentrations were measured by a specific solid phase RIA in random urine samples collected throughout the menstrual cycle of normal menstruating women (n = 8), women with tubal sterilization (n = 6), women taking a low dose oral contraceptive (n = 5), and women throughout pregnancy (n = 52) and delivery (n = 35). There were no differences in EGF concentrations between the proliferative and secretory phases of the menstrual cycle (P greater than 0.05). Normal menstruating women had higher urinary EGF concentrations [mean +/- SE, 37.2 +/- 6.0 micrograms/g creatinine (4.23 +/- 0.68 ng/mumol)] than women with tubal sterilization [32.7 +/- 4.0 (3.71 +/- 0.45)] or women taking a low dose oral contraceptive [19.5 +/- 6.0 (2.21 +/- 0.68)], but the differences were not significant (P greater than 0.05). During pregnancy, urinary EGF concentrations increased linearly from 6-20 weeks gestation (r = 0.76; P less than 0.001), then declined toward term (r = -0.71; P less than 0.001). EGF concentrations in early pregnancy (less than 12 weeks) or at term did not differ significantly from those in normal menstruating women (P greater than 0.05). For women delivering normal, appropriate for gestational age (AGA) infants, there was no correlation between urinary EGF concentrations and fetal weight or sex (P greater than 0.05). Urinary EGF concentrations in women delivering normal AGA infants [52.7 +/- 2.5 (5.98 +/- 0.28); n = 16] did not differ significantly (P greater than 0.05) from those in women with class A/B diabetes [41.9 +/- 2.8 (4.76 +/- 0.31); n = 6] or women delivering twins [45.6 +/- 2.6 (5.18 +/- 0.29); n = 8] with a greater fetoplacental mass. However, women delivering an intrauterine growth-retarded fetus with decreased fetoplacental mass had lower urinary EGF concentrations (24.9 +/- 2.2 (2.83 +/- 0.25); n = 5] than women with normal AGA infants (P less than 0.01). The significance of the rise in the urinary EGF concentration late in the second trimester and lower urinary EGF concentrations in women delivering intrauterine growth-retarded infants is not known, but may reflect an important physiological role for EGF in fetal-maternal hormonal interaction and development.
It is well established that liver microsomal cytochrome P-450 participates in steroid metabolism and probably also in the metabolism of anti-oestrogens such as tamoxifen (Nolvadex). Thus it is possible that variations in cytochrome P-450 levels may influence the responsiveness of human breast and endometrial carcinomas to endocrine therapy. Therefore a simple sensitive spectrophotometric assay for determining levels of cytochrome P-450-dependent cyclohexane hydroxylation activity in breast and uterine microsomes (microsomal fractions) has been developed. Cyclohexane was chosen as a substrate because of the relatively high levels of cyclohexane hydroxylase activity in tumour microsomes and because cyclohexane serves as a substrate for several forms of cytochrome P-450. As previously described [Senler, Dean, Pierce & Wittliff (1985) Anal. Biochem. 144, 152-158], a direct method utilizing isotope-dilution/gas chromatography-mass spectrometry was also developed in order to confirm the results of the spectrophotometric assay. The average activity (cyclohexane-dependent NADPH oxidation) for 139 human breast-tumour microsome preparations was 1.34 nmol/min per mg, which is in the range of that found in untreated mammalian liver (1-3 nmol/min per mg). Also, high enzyme activity was demonstrated in human ovary, normal uterus as well as uterine leiomyomas. Endocrine status appeared to influence enzyme levels, in that mammary tissue from virgin rats contained significantly (P less than 0.025) higher amounts of activity than did tissues from either pregnant or lactating rats. Furthermore, carbon monoxide, as well as an antibody against rat liver cytochrome P-450, completely inhibited NADPH oxidation by breast-carcinoma microsomes. These results strengthen our hypothesis that tumours with high levels of cytochrome P-450 may have a reduced response to additive endocrine therapy.
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