Can 19-nortestosterone derivatives be aromatized in the liver of adult humans? Are there clinical implications?

CONTEXT

Previous studies in postmenopausal women have demonstrated that, after oral administration of norethisterone, a small proportion of the compound is rapidly converted into ethinylestradiol. The shape of the concentration - time curve suggested that this occurred in the liver. The results were confirmed by in vitro investigations with adult human liver tissue. In 2002, it was shown that, after oral treatment of women with tibolone, aromatization of the compound occurred, resulting in the formation of a potent estrogen, 7 alpha-methyl-ethinylestradiol. The result has been called into question, because the adult human liver does not express cytochrome P450 aromatase, which is encoded by the CYP 19 gene. Moreover, it has been claimed that the serum level of 7 alpha-methyl-ethinylestradiol measured by gas chromatography/mass spectrometry was an artifact.

REPLY

Aromatization of steroids is a complex process of consecutive oxidation reactions which are catalyzed by cytochrome P450 enzymes. The conversion of the natural C19 steroids, testosterone and androstenedione, into estradiol-17beta and estrone is dependent on the oxidative elimination of the angular C19-methyl group. This complex key reaction is catalyzed by the cytochrome P450 aromatase, which is expressed in many tissues of the adult human (e.g. ovary, fat tissue), but not in the liver. However, 19-nortestosterone derivatives are characterized by the lack of the C19-methyl group. Therefore, for the aromatization of these synthetic steroids, the action of the cytochrome P450 aromatase is not necessary and the oxidative introduction of double bonds into the A-ring can be catalyzed by other hepatic cytochrome P450 enzymes. The final key process in the formation of a phenolic A-ring, both in natural androgens and 19-nortestosterone derivatives, is the enolization of a 3-keto group to the C2-C3-enol or the C3-C4-enol moiety, which occurs without the action of enzymes.

CONCLUSION

19-nortestosterone derivatives (norethisterone, norethynodrel, tibolone) can readily be aromatized in the adult human liver. This leads to the formation of the potent estrogens ethinylestradiol from norethisterone or norethynodrel and 7 alpha-methyl-ethinylestradiol from tibolone. This may have clinical consequences, e.g. the elevated risk of venous thromboembolic disease in premenopausal women treated with high doses of norethisterone for bleeding disorders, or the elevated risk of stroke or endometrial disease in postmenopausal women treated with tibolone.

The estrogenic activity of synthetic progestins used in oral contraceptives enhances fatty acid synthase-dependent breast cancer cell proliferation and survival

Overexpression of the lipogenic enzyme fatty acid synthase (FAS) is a common molecular feature in subsets of sex-steroid-related tumors including breast carcinomas that is associated with poor prognosis. In this study, we explored whether breast-cancer associated FAS (oncogenic antigen-519) is regulated by the progestin component in oral contraceptives. In addition, we examined the role of FAS hyperactivity on progestin-regulated breast cancer cell proliferation, survival and metastatic properties. We found that in estrogen receptor (ER)- and progesterone receptor (PR)-positive MCF-7 human breast cancer cells, synthetic progestins used in oral contraceptives including norethynodrel (NOR) and norethindrone, induced a dose-dependent increase of FAS enzymatic activity, with a maximum response (> or = 4-fold) occurring at a concentration of 10(-8) M. FAS activity was only slightly stimulated after exposure to two other progestins, medroxy-progesterone acetate (MPA) and megestrol acetate (MGA), which are used in postmenopausal hormone replacement therapy and high-dose progestin treatment therapy. Western blot analyses showed that NOR-induced stimulation of FAS activity correlated closely with NOR-induced up-regulation of FAS protein expression. To determine the role of FAS accumulation following NOR exposure, we pharmacologically examined the requirement for FAS activity in NOR-stimulated breast cancer cell proliferation and survival. The novel small compound C75 (a slow-binding FAS inhibitor) blocked NOR-induced breast cancer cell proliferation in anchorage-dependent assays. More importantly, pharmacological inhibition of FAS activity completely abolished NOR-stimulated soft-agar colony formation of MCF-7 cells. To evaluate the involvement of PR and ER signalings in NOR-induced up-regulation of FAS expression and activity, NOR was used in combination with either the anti-progestin RU486 (mifepristone) or the pure antiestrogen ICI 182,780 (Faslodex). RU486 and ICI 182,780 similarly abolished NOR-induced FAS activation, supporting the notion that PR- and ER-mediated FAS up-regulation might play different roles in NOR-stimulated breast cancer cells. Interestingly, when we evaluated the involvement of PR and ER signalings on NOR-induced breast cancer cell proliferation, the anti-estrogen ICI 182,780, but not the anti-progestin RU486, was found to inhibit NOR-stimulated proliferation and survival of MCF-7 cells in anchorage-dependent and -independent assays. To further determine whether NOR produced their effects via the ER, we evaluated its effects on endogenous ER transcriptional activity by using transient transfection assays with an estrogen-response element reporter construct (ERE-Luciferase). In the absence of E2 stimulation, treatment with NOR dramatically increased the levels of ERE-dependent transcriptional activity. This estrogenic like-effect of NOR was blocked by the addition of ICI 182,780, whereas RU486 failed to inhibit NOR-induced ERE activity. In summary, this study provides direct evidence that: a) a number of synthetic progestins used in oral contraceptives significantly activates breast cancer-associated FAS (OA-519) activity and expression in hormone-dependent breast cancer cells; b) FAS activity is necessary for progestin-induced anchorage-independent growth and survival of human breast cancer cells, and c) activation of ER, but not PR signaling, is the stimulatory mechanism through which synthetic progestins enhance a FAS-dependent proliferative and pro-survival signaling. These findings should be helpful to explain the conflicting evidence linking oral contraceptives and breast cancer risk through the estrogenic activation of tumor-associated FAS (OA-519), a molecular marker associated with poor clinical outcome of breast cancer disease.

An environmentally relevant concentration of estrogen induces arrest of male gonad development in zebrafish, Danio rerio

The aim of the present study was to elucidate how full life-cycle exposure to estrogens impacts zebrafish development and reproduction, compared to partial life-cycle exposure only, and whether the estrogen-induced effects in zebrafish are reversible or irreversible. Zebrafish were exposed in a flow-through system to an environmentally relevant concentration (3 ng/L) of the synthetic estrogen 17alpha-ethinylestradiol (EE2) either from fertilization until the all-ovary stage of gonad development (i.e., 42 d postfertilization [DPF] in our experiment) or from fertilization until the reproductive stage (i.e., 118 DPF). Reversibility of the estrogen-induced effects was assessed after 58 d of depuration in EE2-free water until 176 DPE Early life exposure led to a lasting induction of plasma vitellogenin (VTG) in adult females but altered neither the sex ratio nor the reproductive capabilities. Full life-cycle exposure resulted in elevated VTG concentrations and caused gonadal feminization in 100% of exposed fish and thus inhibited reproduction. Two types of ovaries were observed in continuously exposed adult fish, immature ovaries with primary growth stage oocytes only and mature ovaries containing the full range of all oocyte maturation stages. Fish with immature ovaries had plasma VTG levels like control males, while fish with mature ovaries had female-like VTG levels. The effects of full life cycle exposure were at least partly reversible, and 26% of fish of the previous all-female cohort developed fully differentiated testes. These findings suggest that continuous estrogen exposure had arrested the developmental transition of the gonads of genetic males from the early all-ovary stage to functional testes. After the exposure had ceased, however, these males apparently were able to accomplish testicular differentiation.

Effect of calcium channel modulators on temperature regulation in ovariectomized rats

Clinical studies evaluating a calcium channel modulator, gabapentin, for the treatment of vasomotor symptoms have been reported. The present studies evaluated three calcium channel modulators in ovariectomized (OVX) rodent models of temperature regulation. Gabapentin, reported to interact with the alpha(2)delta subunit of voltage-sensitive calcium channels and the L-type voltage-gated calcium channel blockers, verapamil and nifedipine, were examined. These series of experiments demonstrated that orally administered gabapentin, verapamil and nifedipine all acutely and dose-dependently lower tail skin temperature in both models of OVX-induced thermoregulatory dysfunction. These compounds all had a rapid onset of action, however, the efficacy of all three calcium channel modulators is less than that observed following chronic estrogen treatment. Additionally, these compounds were also tested in a telemetric rat model measuring core body temperature to evaluate any temperature effects on internal core temperature. The present data suggests that gabapentin, verapamil and nifedipine all act to globally alter temperature regulation in steroid-dependent models of thermoregulatory function.

Differential effects of estrogens and progestins on the anticoagulant tissue factor pathway inhibitor in the rat

Oral contraceptives (OC) and postmenopausal hormone therapy (HT) modulate plasma levels of proteins that regulate blood coagulation. It remains unclear whether the progestin component contributes to these changes. The present study was designed to determine whether progestins modulate two essential plasma anticoagulants, antithrombin (AT) and tissue factor pathway inhibitor (TFPI), in an animal model. Ovariectomized rats were treated orally with three progestins, norethindrone acetate (NETA), trimegestone (TMG), or drospirenone (DSP), either alone or combined with 17alpha-ethyinylestradiol (EE). Plasma AT levels were unchanged. However, TFPI activity was reduced by EE alone (10-100 microg/kg/day) in a dose-dependent manner; NETA (3 or 10 mg/kg/day) reduced TFPI by approximately 40 or approximately 80%, respectively, while TMG and DSP had no effect. NETA and EE effects were blocked by co-administration of ICI-182,780, an estrogen receptor antagonist, suggesting that both responses were likely estrogen receptor-mediated. Reduced TFPI after NETA or EE treatment was not accompanied by changes in TFPI mRNA levels in tissues that express TFPI, but there was a positive correlation between plasma TFPI and total cholesterol. Sex hormone effects on TFPI in this model and as reported in women may help to shift the coagulation balance to a more prothrombotic state. Progestins such as TMG and DSP that lack estrogenic activity could potentially have an improved clinical profile.

Removal of estrogenic activity and formation of oxidation products during ozonation of 17alpha-ethinylestradiol

This study investigated the oxidation of the oral contraceptive 17alpha-ethinylestradiol (EE2) during ozonation. First, the effect of ozone (O3) on the estrogenic activity of aqueous solutions of EE2 was studied using a yeast estrogen screen (YES). It could be shown that O3 doses typically applied for the disinfection of drinking waters were sufficient to reduce estrogenicity by a factor of more than 200. However, it proved impossible to completely remove estrogenic activity due to the slow reappearance of 0.1-0.2% of the initial EE2 concentration after ozonation. Second, oxidation products formed during ozonation of EE2 were identified with LC-MS/MS and GC/MS and the help of the model compounds 5,6,7,8-tetrahydro-2-naphthol (THN) and 1-ethinyl-1-cyclohexanol (ECH), which represent the reactive phenolic moiety and the ethinyl group of EE2. Additionally, oxidation products of the natural steroid hormones 17beta-estradiol (E2) and estrone (E1) were identified. The chemical structures of the oxidation products were significantly altered as compared to the parent compounds, explaining the diminished estrogenic activity after ozonation. Overall,the results demonstrate that ozonation is a promising tool for the control of EE2, E2, and E1 in drinking water and wastewater.

Developmental effects of prenatal exposure to bisphenol a on the uterus of rat offspring

Exposure to estrogenic compounds during critical periods of fetal development could result in adverse effects on the development of reproductive organs that are not apparent until later in life. Bisphenol A (BPA), which is employed in the manufacture of a wide range of consumer products, is a prime candidate for endocrine disruption. We examined BPA to address the question of whether in utero exposure affects the uterus of the offspring and studied the expression and distribution of the estrogen receptors alpha (ERalpha) and beta (ERbeta), because estrogens influence the development, growth, and function of the uterus through both receptors. Gravid Sprague-Dawley dams were administered by gavage either 0.1 or 50 mg/kg per day BPA or 0.2 mg/kg per day 17alpha-ethinyl estradiol (EE2) as reference dose on gestation days 6 through 21. Female offspring were killed in estrus. Uterine morphologic changes as well as ERalpha and ERbeta distribution and expression were measured by immunohistochemistry and Western blot analysis. Striking morphologic changes were observed in the uterine epithelium of postpubertal offspring during estrus of the in utero BPA-treated animals (the thickness of the total epithelium was significantly reduced). ERalpha expression was increased in the 50-mg BPA and EE2-treated group. In contrast, we observed significantly decreased ERbeta expression in all BPA- and EE2-treated animals when compared with the control. In summary, these results clearly indicate that in utero exposure of rats to BPA promotes uterine disruption in offspring. We hypothesize that the uterine disruption could possibly be provoked by a dysregulation of ERalpha and ERbeta.

Induction of estrogen receptor-alpha and -beta activities by synthetic progestins

The cellular action of steroid hormones is mediated by specific receptors. Recently, two different estrogen receptors (ER), alpha and beta, have been cloned with a specific tissue distribution. Active estrogen as well as active progestin are compounds of oral hormonal contraceptives and hormone replacement therapy. To examine the regulation of ER-alpha and -beta activities after treatment with synthetic progestins and synthetic and natural estrogens, COS 7 cells were transfected with the vector expressing ER-alpha and -beta in combination with a luciferase reporter vector. ER-alpha activity was upregulated in the presence of synthetic progestins in a dose-dependent manner. Norethisterone, norethynodrel and desogestrel proved to be the most potent stimulatory agents of ER-alpha expression. On the other hand, not all progestins exhibited a stimulatory action on ER-beta activity. Only norgestrel, levonorgestrel, norethynodrel and norethisterone induced ER-beta-activating functions in a dose-dependent manner. Luciferase activity due to estrogen stimulation served as a positive control. Our results indicate that progestins have different effects on the activities of ER-alpha and -beta.

The effects of progesterone and progestins on endometrial proliferation

A total of 99 premenopausal and 27 postmenopausal women were evaluated to determine the quantity of glandular proliferation resulting from progestin inhibition of estrogen-primed subjects and of subjects without hormonal stimulation. Endometrial glandular proliferation rates were determined by using mitosis counts, proliferating-cell nuclear antigen (PCNA), and nuclear cyclin (MIB1) immunocytological staining. The endometria of normally cycling premenopausal women, of women who received a synthetic progestin, and of untreated postmenopausal women were studied. In untreated normally cycling premenopausal women, the proliferation of the glandular epithelium was increased during the follicular phase and decreased during the luteal phase. Premenopausal women receiving a synthetic progestin and untreated postmenopausal women who were not estrogen-primed showed minimal epithelial proliferation. Endometrial glandular proliferation is inhibited by endogenous progesterone in premenopausal women. Endometrial proliferation is markedly reduced in premenopausal women receiving a synthetic progestin and in untreated postmenopausal women.

Progestin regulation of vascular endothelial growth factor in human breast cancer cells

Vascular endothelial growth factor (VEGF) is a potent angiogenic factor associated with the degree of vascularity, progression, and metastasis of breast cancer, and cases of this disease with increased vascular density have a poor prognosis. We show that in T47-D human breast cancer cells, progesterone induces a dose-dependent increase of 3-4-fold in media VEGF levels, with a maximum response occurring at a concentration of 10 nM. This effect is blocked by the antiprogestin RU 486. In addition to progesterone, a number of synthetic progestins used in oral contraceptives (e.g., norethindrone, norgestrel, and norethynodrel), hormone replacement therapy (medroxyprogesterone acetate), and high-dose progestin treatment of breast cancer (megestrol acetate) also increase VEGF in the media of cultured T47-D cells. This effect is hormone specific and is not produced by estrogens, androgens, or glucocorticoids. Collectively, these observations suggest that the increase in VEGF caused by progestins is mediated by progesterone receptors present in T47-D cells. The induction of VEGF by progestins is also cell type specific and does not occur in human breast cancer cell lines MCF-7, ZR-75, or MDA-MB-231, nor in Ishikawa cells derived from a human endometrial carcinoma. This is the first report that progestins regulate VEGF expression in human breast cancer cells and raises the possibility that increased angiogenesis in response to endogenous progesterone or its therapeutically used analogues may play a role in cell growth or metastasis in a subset of human breast tumors.

Estrogenic potential of progestins in oral contraceptives to stimulate human breast cancer cell proliferation

Most oral contraceptives (OC) contain a progestin in combination with an estrogen, and the progestin component in OC includes one of the following 19-nortestosterone derivatives: norethynodrel; norethindrone; or norgestrel (levonorgestrel). It is well known that estrogens promote the growth of breast cancer. However, progestins have recently also been implicated in the development of breast cancer. We have compared and contrasted the ability of synthetic progestins to stimulate the proliferation of cultured human breast cancer cells and examined their possible mechanism of action. We found that some progestins used in OC were able to stimulate the growth of estrogen receptor-positive (ER+) MCF-7 and T47DA18 human breast cancer cells but not ER- MDA-MB-231, BT-20, and T47DC4 human breast cancer cells. However, two other progestins, MPA and R5020, which are not used in OC, were either not able to stimulate or only slightly stimulated growth. The potency of norethynodrel [median effective dose (EC50) = 4 x 10(-8) M] and norethindrone (EC50 = 3 x 10(-8) M) was greater than norgestrel (EC50 = 2 x 10(-7) M) in MCF-7 cells. E2 (EC50 = 8 x 10(-13) M) was an even more potent stimulator of growth. More importantly, the progestin-induced growth stimulation was blocked by the antiestrogens 4-hydroxytamoxifen and ICI 164,384 but not the antiprogestin 17 beta-hydroxy-11 beta-(4-dimethylaminophenyl)-17 alpha-(1-propynyl)-estra-4, 9-dien-3-one (RU486). To determine whether the proliferative action of progestins was mediated through the ER, cells were transfected with a chloramphenicol acetyltransferase reporter gene containing an estrogen response element derived from vitellogenin 2A gene. The progestins which stimulated the growth of breast cancer cells also increased chloramphenicol acetyltransferase activity. The induction of chloramphenicol acetyltransferase activity was blocked by the addition of the antiestrogens 4-hydroxytamoxifen and ICI 164,384 but not the antiprogestin RU486. This study provides direct evidence that the 19-nortestosterone derivatives in OC have estrogenic properties and suggests that activation of ER, but not progesterone receptor, is the growth-stimulatory mechanism for these synthetic progestins. Our results may help to explain the conflicting evidence linking OC and breast cancer risk. A rigorous evaluation of the "total" estrogenic potential of OC might produce a better correlation with breast cancer risk.

The hormonal regulation of platelet-activating factor-acetylhydrolase in the rat

Platelet-activating factor-acetylhydrolase (PAF-AH), the enzyme that inactivates PAF, is decreased in the plasma of both rabbits and humans during the latter stages of pregnancy. The activity of the enzyme was decreased in rats by the administration of 1,3,5(10)-estratrien-17 alpha-ethynyl-3,17 beta-diol (17 alpha-ethynylestradiol) and increased by dexamethasone treatment. In the present study, we have further defined the hormonal regulation of PAF-AH levels in plasma of adult and juvenile rats. Estrone (E1), 17 beta-estradiol (E2), estriol (E3), and various progestins [4-pregnen-6 alpha-methyl-17 alpha-ol-3,20-dione (medroxyprogesterone), 4-estren-17 alpha-ethynyl-17 beta-ol-3-one (norethindrone), and 5(10)-estren-17 alpha-ethynyl-17 beta-ol-3-one (norethynodrel)] were administered to adult rats, and the plasma PAF-AH activities were assayed. E1, E2, and E3 administration to adult female rats lowered the plasma PAF-AH activity, E3 being the most effective. After administration of these estrogens the activity returned to the preinjection level within 4 days. The administration of medroxyprogesterone resulted in a 2-fold increase in plasma PAF-AH activity in adult female rats, and the activity remained elevated for up to 30 days. When adult male rats were treated with similar doses only a 20% increase was observed and the PAF-AH activity returned to control values by day 10. In contrast, norethindrone and norethynodrel administration resulted in a reduction of the enzyme activity in adult female rats. The plasma PAF-AH activity in juvenile male and female rats (3 weeks of age, 45-60 g body wt) was two times higher than that in adult rats of both sexes and spontaneously decreased up to the time of puberty. When juvenile male or female rats were injected with either 17 alpha-ethynylestradiol or medroxyprogesterone, a minimal change in PAF-AH activity was observed. In contrast, when dexamethasone was administered to juvenile male and female rats the plasma PAF-AH activity increased in a manner similar to adult animals. It is suggested that estrogens cause a decrease and medroxyprogesterone an increase in plasma PAF-AH activity. It is suggested that the different responsiveness to medroxyprogesterone between adult female and male rats and juvenile animals may depend on the concentration of the hormone receptor in the tissue responsible for the synthesis of PAF-AH. The decrease in PAF-AH activity after the administration of norethindrone and norethynodrel may be due to the known estrogenic activity of these steroids.

Hormone prevention of mammary carcinogenesis by norethynodrel-mestranol

The observation that the susceptibility of the mammary gland to chemical carcinogenesis is inversely related to its level of hormonally induced differentiation led us to test whether treatment of virgin rats with an estrogenic-progestagenic hormone combination protected the gland against this carcinogenesis. Virgin Sprague-Dawley rats aged 45, 55, 65, or 75 days had implanted subcutaneously for 21 days a pellet containing norethynodrel-mestranol (NM) (98.5%-1.5%) at two doses, a physiological or low dose (LD) of 0.5 mg, equivalent to the dose used in Enovid for contraception in humans, and a pharmacological or high dose (HD) of 5.0 mg. Twenty-one days after NM pellet removal, the mammary glands of 5 animals per group were examined for the number of terminal end buds (TEBs), terminal ducts (TDs), alveolar buds (ABs) and lobules, and the DNA labeling index (DNA-LI). The remaining animals received 8 mg 7,12-dimethylbenz(a) anthracene (DMBA)/100 g body weight, and tumorigenesis was evaluated at 24 weeks. The percentage of TEBs decreased with age, and further with NM treatment at both doses. Treatment did not significantly modify the percentage of TDs, but increased that of ABs in most groups. The DNA-LI of TEBs remained constant, even during aging and after treatment, whereas both aging and treatment reduced DNA-LI in TDs and ABs. Tumor incidence declined with increasing age from 75% to 44% in the 45 and 75 day-old control groups respectively. Adenocarcinoma incidence followed the same trend. NM treatment had a dose-related protective effect against development of tumors in general and of adenocarcinomas in particular. LD treatment resulted in a marginally significant reduction in adenocarcinoma incidence, whereas HD-treated animals were 0.24 times as likely as controls to develop carcinomas. There was a statistically significant correlation between the percentage of TEBs present in the gland at the time of carcinogen administration and the incidence of adenocarcinomas. It was concluded that treatment of virgin rats with the hormone combination norethynodrel-mestranol resulted in long lasting structural changes in the mammary gland which protected this organ from a subsequent carcinogenic insult.

A-ring reduction enhances the antigonadotropic potency of norethisterone

To assess whether structural modifications on the A-ring of norethisterone (NET) could modify its antigonadotropic potency, comparative studies using NET, 5 alpha-dihydro NET (5 alpha-NET) and its 3 beta,5 alpha and 3 alpha,5 alpha tetrahydro derivatives in castrated adult rats were undertaken. The antigonadotropic effect of these compounds was evaluated by measuring the serum and pituitary immunoreactive concentrations of LH and FSH following their chronic sc administration to animals depleted of progesterone receptors. The results demonstrated that 3 beta,5 alpha-NET and 5 alpha-dihydro-NET exhibited a significantly greater gonadotropic inhibiting activity as compared with that of their parent compound. The simultaneous administration of tamoxifen with 3 beta,5 alpha-NET resulted in a significant diminution of its antigonadotropic potency, particularly for LH. These data indicate that the potent antigonadotropic effect of 3 beta,5 alpha-NET metabolite was mediated via oestrogen receptors. The LH inhibitory activity of 5 alpha-dihydro-NET was not suppressed by the non-steroidal antioestrogen administration, thus suggesting that 5 alpha-NET might exert its effect via androgen receptors. The overall data were interpreted as demonstrating that metabolic conversion products of NET exhibit potent antigonadotropic effect. The data are consistent with an A-ring enhancement of the antigonadotropic potency of this synthetic progestin and open an alternate approach to the development of fertility regulating agents.

Effect of tumor promoting contraceptive steroids on growth and drug metabolizing enzymes in rat liver

Liver tumor formation in rats treated with oral contraceptive steroids for long periods has been associated with the tumor promoting potential of these agents. As other known liver tumor promoters, e.g., phenobarbital and hexachlorocyclohexane, induce liver growth and hepatic monooxygenases, we investigated whether or not estrogens have similar effects. Female rats were treated with a wide range of doses of ethinylestradiol, including human contraceptive doses, which are approximately 1 microgram/kg. The physiological estrogen estradiol was studied for comparison. Also included were norethynodrel and norethisteron and its acetate and enanthate because these human progestins act predominantly estrogenic in rats. Daily s.c. doses of ethinylestradiol (0.5 mg/kg) produced a rapid increase of liver mass, DNA, RNA, and protein which was almost maximal after 7 days. The percentages of parenchymal cells involved in DNA synthesis and mitosis were enhanced up to 20-fold, suggesting parenchymal hyperplasia as the main cause of liver growth. Sinus wall cells showed a proportionate increase of number and DNA synthesis. Likewise, all other steroids tested produced significant increases of liver mass and DNA. For ethinylestradiol and estradiol extrapolated threshold doses were in the range of 1 microgram/kg. These doses are below those used in previous tumor promotion studies in rats. Using 5 different substrates to check monooxygenase activities of isolated liver microsomes, no induction or only very weak induction by estrogens was found. These studies suggest that induction of liver growth may be a property relevant for the tumor promoting activity of estrogens; in contrast, induction of hepatic monooxygenases does not appear to be necessary for liver tumor promotion in the rat.

Evidence that a non-aromatizable metabolite of norethisterone induces estrogen-dependent pituitary progestin receptors

Neutral reduced metabolites of norethisterone (NET) specifically interact with intracellular estrogen receptors in target organs. To determine if this interaction can effectively initiate estrogen-dependent cellular responses, the effects of an A-ring-reduced NET derivative upon the induction of cytosol-located pituitary progestin receptors (PR) and uterine growth were studied in adult castrated female rats. Different doses of 17 alpha-ethynyl-5 alpha-estran-3 beta, 17 beta-diol (3 beta, 5 alpha-NET) were s.c. administered to ovariectomized animals for 6 days. 17 beta-Estradiol (E2) and oil-treated rats served as experimental controls. Pituitary PR were labeled in vitro by a post-gradient technique using [3H]ORG-2058 as the ligand. PR binding specificity was determined by the use of an excess of radioinert steroids. The results demonstrated that administration of 3 beta, 5 alpha-NET induced specific 8-9S pituitary cytosol PR in a dose-dependent manner. Binding properties of the 3 beta, 5 alpha-NET-induced progestin binding sites (Kd = 1.0 X 10(-9) M; NBS = 1.2 X 10(-9) M) appear indistinguishable from those induced by E2. In addition, 3 beta, 5 alpha-NET administration resulted in a significant increase in uterine weight at the expense of myometrium and endometrium growth in a similar fashion to that observed in the E2-treated group. When 3 alpha, 5 alpha-epimeric alcohol (3 alpha, 5 alpha-NET) was administered, induction of pituitary PR and uterine growth were also observed although to a lesser extent. Inasmuch as the results demonstrate that neutral non-aromatizable NET metabolites induce biochemical and morphological estrogenic responses, they offer an alternative explanation for the mechanism of estrogen-like action of this synthetic contraceptive progestin.

Effect of a steroidal oral contraceptive on intestinal absorptive functions in proteins deficient rat

The effects of steroidal oral contraceptive norethynodrel plus ethinylestradiol-3-methyl ether (SOC) at a daily dose of 5 mg: 0.06 mg per kg body weight for 28 days on intestinal absorptive functions have been investigated in protein-deficient female albino rats. The administration of this contraceptive caused significant increase in glucose and amino acids uptake but had no effect on calcium and zinc uptake in pair-fed as well as in protein-deficient rat. Further studies carried out on glucose transport system showed that the transport of sodium-dependent glucose was significantly enhanced while that of sodium-independent glucose remained unaltered in drug-treated animals. Kinetic studies of glucose transport in the presence of sodium ions revealed that SOC treatment affected the rate of uptake of glucose by elevating Vmax, but the apparent Kt value remained the same in treated and untreated animals.

Effect of some synthetic steroids on rat liver function

Norethynodrel proved to have moderately potent effects on hepatic function in female rats. It causes (a) loss of body mass, (b) increase in the relative liver mass, (c) rise in the protein content of liver, (d) increase in the cytochrome P-450 level, (e) reduction in the length of pentobarbital-induced sleep, and (f) increase in the rate of biotransformation of (i) aniline and (ii) aminopyrine. In contrast, ethynyl estradiol was shown to have little or no effect as judged by the same criteria, but, like norethynodrel, progesterone and estradiol, caused loss of body mass.

Synthetic progestins and sweetness preference in intact female Sprague-Dawley rats

Intact Sprague-Dawley female rats were treated with 0.25 microgram or 1.25 micrograms ethinyl-estradiol (EE) in combination with one of 3 synthetic progestins: (5 micrograms) norethindrone, norethynodrel, or norgestrel. In Experiment 1 both dosages of EE in combination with the synthetic progestins suppressed sweetness preference, with a somewhat greater effect for the 1.25 micrograms EE dosage. Norgestrel in combination with EE produced the longest suppression of sweetness preference. In Experiment 2 progestins administered in the absence of EE showed no significant effect on sweetness preference. When 1.25 micrograms EE was administered singularly, a significant decline in sweetness preference occurred, but not as great a decline as in combination with a progestin.

Effects of norethynodrel on neoplasms in the buccal pouch of the Syrian hamster

This study was instituted to determine the effect of a progestin, norethynodrel, on the induction of experimental carcinogens of the hamster cheek pouch. Thirty-six Syrian hamsters were divided into two groups. One group received 2 mg./kg./day of norethynodrel in subcutaneous injections, and the other group received nothing. The right cheek pouches of both groups were painted three times a week with the chemical carcinogen 9,10-dimethyl-1,2-benzanthracene in a 0.05 percent acetone solution. After 9 weeks of painting, the first tumors developed in the hormone-treated hamsters, while none appeared in the control group until after 10 weeks. After 15 weeks, 100 percent of both groups had tumors. The average latent period was 11.8 weeks for the treated group and 12.7 weeks for the control group (p = less than 0.05 percent, Student's test). Norethynodrel significantly decreased the induction time of the neoplasms.

The binding of 7,12-dimethylbenz[a]anthracene to mammary gland macromolecules in the hamster:effects of Enovid feeding or transplacental exposure to diethylstilboestrol

The covalent binding of 7,12-[3H]dimethylbenz[a]anthracene ([3H--DMBA) to mammary gland macromolecules was studied in hamsters fed a contraceptive mixture, Enovid, those exposed transplacentally to diethylstilboestrol (DES), and controls. Compared with rats, hamsters are relatively resistant to DMBA mammary carcinogenesis, but susceptibility is increased by either of the above treatments with Enovid or DES. The amount of DMBA bound to DNA and protein ws 4-5 times greater than to RNA, but only DNA binding was persistent. Fifty-three percent of the DNA-bound DMBA was still present after 8 days. The amount of DMBA bound to hamster mammary DNA and its persistence was similar to that found in rats. Neither Enovid nor DES treatment altered the levels of binding to mammary macromolecules, nor their persistence. These results indicate that the species differences in the susceptibility to DMBA-induced mammary carcinogenesis in hamsters and rats, and modification of the former by hormones, is not due to differences in the activation of carcinogens. The role of hormones such as prolactin in the promotion phase of mammary gland carcinogenesis may explain these differences.

Increased synthesis of aortic collagen and elastin in experimental atherosclerosis. Inhibition by contraceptive steroids

Rabbits were fed an atherogenic or normal control diet for 3 months; half of each group were treated with mestranol--norethynodrel (M--N) and half with cottonseed oil vehicle. At the end of the 3-month period rabbits were killed and aortic collagen and elastin synthesis determine. Collagen and elastin synthesis was increased in aortas of rabbits on an atherogenic diet, but those treated with M--N had a lower rate of collagen synthesis and less deposition of cholesterol in the aorta than those administered cottonseed oil. It is suggested that long-term administration of the contraceptive steroid combination may retard the progression of atherosclerosis through the hormone's effect on vascular connective tissue.

Enovid-induced exacerbation of high blood pressure in stroke-prone rats (SHR)

Male and female, normotensive Wistar:Kyoto rats, spontaneously hypertensive rats (SHR), and Stroke-prone SHR (SHR/SP) with severe hypertension were treated with a contraceptive drug (Enovid) from the time of weaning until they became 180 days old. Although the Envoid-treated SHR and SHR/SP had exacerbations of their high blood pressure, none of the animals developed renal or cerebral damage. Chronic treatment with Enovid caused testicular and ovarian atrophy and a significant increase in circulating corticosterone. It is suggested that the potentially deleterious effects, e.g., stroke, hypertension, hyperglycemia, hyperlipidemia, etc., of chronic treatment with contraceptive drugs is largely determined by pre-existing genetically endowed proneness or resistance.

Tolerance of estrogen-treated rats to acute cold exposure

Female rats treated chronically with ethynylestradiol (36 micrograms/kg per day) alone, and in combination with the progestational agent, norethynodrel (253 micrograms/kg per day), cooled significantly faster than controls when lightly restrained and exposed to air at 5 degrees C. Rate of cooling of rats given only norethynodrel was similar to that of the control group. In other studies, rate of oxygen consumption was determined for all groups during acute exposure to cold (14 degrees C). All estrogen-treated groups achieved the same maximal rate of oxygen consumption as control and norethynodrel-treated groups during cold exposure, but cooled significantly faster. Two groups of female rats were treated chronically with ethynylestradiol at two separate doses (36 and 61 micrograms/kg per day). An untreated group served as controls. Rate of oxygen consumption of all animals were measured during restraint and exposure to cold (18 degrees C). The estrogen-treated groups again achieved the same maximal rate of oxygen consumption as the control group, but also cooled significantly faster despite the fact that the cold stress was less severe than in the previous experiment. That estrogen-treated rats cooled faster than controls in both studies despite achieving a maximal rate of heat production which did not differ from controls suggests that reduced cold tolerance of estrogen-treated rats may be related to increased heat loss.

Effects of oral contraceptives on zinc and copper levels in human plasma and endometrium during the menstrual cycle

Effects of Ovulen-21, Demulen, Enovid-E and Ovral on zinc and copper levels in human plasma and endometrium during the menstrual cycle have been studied. Both plasma and endometrium copper levels were significantly elevated above the control values (P less than 0.001) in women taking oral contraceptives while the zinc levels remained reasonable constant.

Prolactin and the development and progression of early neoplastic mammary gland lesions

Chronic suppression of prolactin by 2-bromo-alpha-ergocryptine (CB-154) in young nulliparous or mature multiparous C3H mice sharply suppressed the development of preneoplastic mammary gland lesions (hyperplastic alveolar nodules) and markedly inhibited the progression of these preneoplasias to carcinomas. This effect was also observed in C3H mice treated with either 17beta-estradiol or the oral contraceptive Enovid. Chronic CB-154 induced prolactin suppression was more effective than ovariectomy in the suppression of hyperplastic alveolar nodule development and comparable to ovariectomy in the suppression of mammary carcinoma development. Evidence is also provided indicating that human placental lactogen, a peptide chemically and physiologically similar to prolactin, promotes growth both in vitro (organ culture) and in vivo (athymic "nude" mouse) of the epithelium contained in benign human breast tumors. Whether or not human pituitary prolactin is capable of mimicking the mammotrophic action of human placental lactogen and whether a dysplastic, prolactin-sensitive lesion comparable to hyperplastic alveolar nodules exists in the human breast remains to be determined.

[Effect of an estrogen-progestin contraceptive preparation on the enzymatic acitivity of the pentosephosphate carbohydrate metabolic pathway and nucleic acid metabolic indices]

The effect of a long-term (14 days) combined introduction of mestranol and noiethinodrel in contraceptive doses on the activity of pentosophosphate routes enzymes of the carbohydrates metabolism, that of acid and basic ribonucleases and on the level of summary nucleinic acids in the uterus and liver in sexually mature female-rats was studied. It was found that the concentration of summary nucleinic acids in the tissues increases under the effect of the drug, the oxidative reactions enzymes become more active, while the activity of non-oxidative reactions enzymes of the pentosophosphate route and of acid and basic endoribonucleases in inhibited.

The metabolism and motility of human spermatozoa in the presence of steroid hormones and synthetic progestagens

The metabolism and motility of human ejaculated spermatozoa incubated in vitro with steroids were studied. Progesterone and norethynodrel depressed the respiration, glycolytic metabolism and the motility of washed spermatozoa. Lynoestrenol did not affect the respiration or glycolysis of the spermatozoa, but did inhibit motility. Oestradiol did not cause any consistent alteration of the sperm metabolism, and did not affect the motility. Progesterone and norethynodrel appeared to act on the plasma membrane of human spermatozoa to increase its permeability and hence to facilitate the loss of essential cofactors required for the glycolytic and oxidative processes.

Free testosterone concentration in serum: elevation is the hallmark of hirsutism

A simple, reliable procedure for quantitating the concentration of free (not protein bound and thus biologically active) testosterone in serum has been applied to normal and hirsute patients. Each of 32 hirsute women studied had a significantly elevated level of free testosterone (that is, more than two standard deviations above the mean of that found in normal women), although half of them had a total serum testosterone level within normal limits. Suppression of free testosterone to within normal limits could be accomplished by dexamethasone alone in 47 per cent of the hirsute group. In the remainder of the hirsute group, suppression of free testosterone to within normal limits could be accomplished by addition of Enovid-E. Use of free serum testosterone concentration is clearly superior to the use of total serum testosterone concentration for the identification and rational therapy of simple hirsutism.

Responsiveness to various dipsogenic stimuli in rats treated chronically with norethynodrel, ethinyl estradiol and both combined

Administration of the estrogen, ethinyl estradiol (36 microng/kg/day), alone, and in combination with the progestogen, norethynodrel (165 microng/kg/day), significantly attenuated the dipsogenic response characteristically induced by acute s.c. administration of the beta adrenergic agonist, dl-iosproterenol (50 microng/kg). Attenuation was apparent within 1 week of steroid treatment, and remained during the 4 weeks of testing. After 16 weeks of steroid treatment, the drinking response to acute i.p. administration of renin (2 and 4 Goldblatt units/rat) was tested. The groups receiving ethinyl estradiol alone, and in combination with norethynodrel, but not norethynodrel alone, showed a reduced water intake compared with untreated controls. Drinking induced by administration of hypertonic saline (1% of body weight of 1 M NaCl solution, i.p.) was also reduced in rats treated with the estrogenic, but not the progestational, agent. However, estrogen treatment did not affect drinking after a 24-hour period of dehydration. Although the reduced dipsogenic response to isoproterenol observed in estrogen-treated rats may reflect a reduced renin secretion, drinking could not be induced in these animals by administration of renin. In addition, the reduced dipsogenic response to hypertonic NaCl loading suggests that estrogens may inhibit thirst mechanisms centrally. Dehydration, which combines hypovolemic and osmotic thirst situmul was, however, sufficient to overcome the reduced dipsogenic responsiveness of estrogen-treated rats.

Response of heart rate to acute administration of isoproterenol in rats treated chronically with norethynodrel, ethinyl estradiol, and both combined

Chronic (17 to 20 weeks) administration of ethinyl estradiol alone (36 mug/kg/day), and in combination (27 or 50 mug/kg/day) with several doses of norethynodrel (135, 165 or 233 mug/kg/day), attenuated the increase in heart rate accompanying acute SC administration of the beta-adrenergic agonist, l-isoproterenol (50 or 100 mug/kg), to female rats. Dietary administration of an oral contraceptive containing mestranol and norethynodrel (7.5 mg/kg/food) was also accompanied by an attenuated response to isoproterenol. A significant inverse linear relationship was observed between the logarithm of the dose of estrogen received by each group and either heart rate or change in heart rate measured at 10, 20 and 30 min after administration of isoproterenol. Thus, the antagonistic relationship between the dose of estrogen administered chronically and responsiveness of heart rate to a test dose of isoproterenol suggests a reduced beta-adrenergic responsiveness in estrogen-treated rats.

Induction of microsomal drug metabolizing enzymes by oral contraceptives in protein-malnourished rats

In order to examine effects of oral contraceptives (OC) on the microsomal drug matabolizing enzymes in a state of protein malnutrition, weanling Sprague-Dwayley female rats were fed diets containing 3.5% (low protein, LP), 26% (normal protein, NP) or 42% (high protein, HP) casein for 224 days and norethynodrel plus mestranol for the last 182 days. LP rats were smaller in body weight than NP and HP rats and the latter two groups showed depressed weight gain and hypertrophy of liver and kidney due to OC. Concentrations of microsomal proteins and cytochrome P-450 were lowered by LP diet and OC did not induce cytochrome P-450. Activity of biphenyl-4-hydroxylase was lowered in LP and HP rats compared to NP group in which activity of this enzyme was significantly decreased due to OC. The diets alone had no effect on the activity of p-nitrobenzoate reductase, however, its activity was enhanced by OC only in NP rats. LP diet caused reduction of 4-methylumbelliferone glucuronly transferase activity which was lowered by OC in NP as well as in LP rats. It is concluded that NP diet more than either LP or HP diet exposed rats to the modification of microsomal drug metabolizing enzymes by OC.

Effects of contraceptive agents on drug metabolism in various animal species

The effect on liver microsomal enzyme activity of three steroid contraceptive drug (SCD) combinations was compared in rats, mice and guinea-pigs. Lynestrenol plus mestranol, norethisterone plus mestranol and norethynodrel plus mestranol were given orally for 4 consecutive days (acute treatment) or 30 days (chronic treatment) at various doses eliciting an experimentally controlled antifertility activity which varied in its extent. In rats and mice all the combined treatments (with the exception of norethynodrel plus mestranol in mice) were active as inducers of liver microsomal enzymes. This induction seems to be mediated mainly by the progestogenic compounds. Oestrogens showed a very poor effect bordering on significance only in a few cases. No effect on liver microsomal protein or cytochrome P 450 concentration was obtained after treatment with doses capable of increasing the microsomal enzyme activity. The activity of the liver microsomal enzymes did not appear to be reduced immediately (2 h) after the last administration of the SCD given during 4 or 30 days. Contraceptive treatments at doses capable of eliciting complete antifertility activity were inactive on liver microsomal enzyme activity in guinea-pigs.

Reduced beta adrenergic responsiveness in rats treated with estrogenic agents

Chronic treatment with ethynyl estradiol alone (48-50 mug/kg/day) and in combination with several doses of norethynodrel either attenuated or prevented the increase in tail skin temperature accompanying sC. administration of isoproterenol (200 mug/kg b.wt.) to male and female rats. Dietary administration of an oral contraceptive containing norethynodrel and mestranol (7.5 mg/kg of food) was also accompanied by an attenuated response to isoproterenol. Attenuation of the tail skin temperature response was present in all groups after 3 to 5 weeks of treatment but was detectable in the oral contraceptive-treated group after 1 week of treatment. All steroids and combinations, except norethynodrel administered alone (154 mug/kg/day), reduced body weight gain.

Heparin metabolism and heparin-release lipase activity during long-term estrogen-progestin treatment

Short-term oral contraceptive therapy has been reported to decrease postheparin lipolytic activity (PHLA). Resistance to heparin has been held responsible for this effect. To test several alternative explanations, we studied both PHLA and heparin concentrations in nine control women and nine women receiving long-term estrogen-progestin therapy after they were given heparin intravenously (10 units/kg). There were no significant differences in the concentration of heparin, its rate of disappearance, or calculated space of distribution between control and treated groups. PHLA was depressed (p less than 0.05) by approximately 50% during long-term estrongen-progestin therapy. PHLA disappearance was similar in both groups. Thus, reduced PHLA in women receiving long-term oral contraceptive therapy cannot be related to altered heparin metabolism or to accelerated enzyme disappearance from plasma. Long-term estrogen-progestin administration may decrease the heparin-facilitated release of individual triglyceride hydrolase activities or enhance the affinity of enzyme binding to tissues.