Direct inhibition of tyrosine hydroxylase activity by catechol estrogens

Sex differences in heart failure medications targeting the renin-angiotensin-aldosterone system

Heart failure (HF) is a major healthcare problem. Sex-related differences in clinical manifestations, outcomes, risk factors and symptoms in HF have been described in the literature. Sex-related differences have also been described in the regulation of the renin-angiotensin-aldosterone system (RAAS), which is at the core of the pathophysiology of HF. Considering that drugs targeting RAAS are cornerstones in the treatment of HF, it is important to determine whether sex-related differences exist in the use of angiotensin converting enzyme inhibitors (ACEIs), angiotensin receptor blockers (ARBs), mineralocorticoid receptor antagonists (MRAs) and ARB/neprilysin inhibitors (ARNIs). In regards to the relative efficacy of RAAS drugs in men vs. women in HF, there are conflicting results, which may stem from the fact that a lot of clinical trials were not specifically designed to investigate sex differences, with many of them having an underrepresentation of women. With respect to optimal dosage of RAAS drugs, even though, current HF guidelines, recommend up-titration to the same target dose in both men and women, evidence suggests that lower doses could be used in women. Furthermore, several studies have reported underutilization of guideline-directed medical therapy in women, including ACEIs, ARBs and MRAs, which may be at least partially attributed to increased prevalence of HF with a preserved ejection fraction and increased propensity for adverse effects in women. Overall, these investigations have shed some light on sex-related differences but there is scope for conducting further studies to determine the optimal use of RAAS drugs in men and women with failing hearts.

Addiction and Dopamine: Sex Differences and Insights from Studies of Smoking

Mesolimbic dopaminergic function influences addiction through effects on reinforcement learning, decision-making, and impulsivity. This review covers sex differences in dopaminergic neurochemistry, their hormonal and genetic determinants, and how differences in dopaminergic tone interact with sex and/or ovarian hormone status to affect cognitive functions. Findings from research on cigarette smoking reveal sex differences in striatal and midbrain dopamine D2-type receptor availability and striatal dopamine release that suggest mechanisms of nicotine dependence, and stronger subjective responses to nicotine and efficacy of nicotine replacement therapies in male smokers than in their female counterparts. Opportunities exist to extend such efforts in studies of how sex and hormone status influence other addictions.

Should there be sex-specific criteria for the diagnosis and treatment of heart failure?

All-cause mortality from cardiovascular disease is declining in the USA. However, there remains a significant difference in risk factors for disease and in mortality between men and women. For example, prevalence and outcomes for heart failure with preserved ejection fraction differ between men and women. The reasons for these differences are multifactorial, but reflect, in part, an incomplete understanding of sex differences in the etiology of cardiovascular diseases and a failure to account for sex differences in pre-clinical studies including those designed to develop new diagnostic and treatment modalities. This review focuses on the underlying physiology of these sex differences and provides evidence that inclusion of female animals in pre-clinical studies of heart failure and in development of imaging modalities to assess cardiac function might provide new information from which one could develop sex-specific diagnostic criteria and approaches to treatment.

Fatty acid composition and lipogenic enzyme protein expression in subcutaneous adipose tissue of male pigs vaccinated against boar taint, barrows, and entire boars

Objectives of this study were to compare fatty acid composition of subcutaneous adipose tissue of entire boars, barrows, and male pigs vaccinated against boar taint with a vaccine containing a GnRH analogue-protein conjugate (Improvac, Pfizer Animal Health) and to investigate the association between fatty acid composition and protein expression of key lipogenic enzymes in entire boars, barrows, and vaccinated pigs. Differences between groups were observed in the content of total SFA (P≤0.001), MUFA (P=0.035), and n-6 PUFA (P≤0.001) but not n-3 PUFA (P=0.373). Total SFA were greater (P<0.001) in barrows and vaccinated pigs compared with entire animals. This was accompanied by an increase (P<0.05) in the protein expression of the lipogenic enzyme fatty acid synthase in barrows and vaccinated pigs. Total MUFA content was increased (P<0.001) in barrows compared with entire and vaccinated pigs. This was not accompanied (P>0.05) by an increase in expression of stearoyl-CoA desaturase protein, the enzyme catalyzing MUFA biosyntheses. Total n-6 PUFA content did not differ (P<0.001) between entire and vaccinated pigs but was lower in barrows. Expression of Δ6-desaturase protein, one of the key enzymes of PUFA biosynthesis, was greater (P<0.05) in vaccinated pigs than in barrows but did not differ significantly between vaccinated and entire animals. We conclude that fatty acid profile of animals vaccinated against boar taint is similar to that of entire male pigs and that the effect of physical castration and vaccination on fatty acid composition involves changes in lipogenic enzyme protein expression.

A novel role for an endothelial adrenergic receptor system in mediating catecholestradiol-induced proliferation of uterine artery endothelial cells

Sequential conversion of estradiol-17β to its biologically active catecholestradiols, 2-hydroxyestradiol (OHE(2)) and 4-OHE(2), contributes importantly to its angiogenic effects on uterine artery endothelial cells (UAECs) derived from pregnant, but not nonpregnant ewes via an estrogen receptor-independent mechanism. Because catecholestradiols and catecholamines exhibit structural similarities and have high affinity for α- and β-adrenergic receptors (ARs), we investigated whether the endothelial α- or β-ARs mediate catecholestradiol-induced proliferation of P-UAECs and whether catecholamines alter these responses. Western analyses revealed expression of specific AR subtypes in nonpregnant UAECs and P-UAECs, including α(2)-, β(2)-, and β(3)-ARs but not α(1)- and β(1)-ARs. Levels of β(2)-ARs and β(3)-ARs were unaltered by pregnancy, whereas α(2)-ARs were decreased. Norepinephrine and epinephrine increased P-UAEC, but not nonpregnant UAEC proliferation, and these effects were suppressed by propranolol (β-AR blocker) but not phentolamine (α-AR blocker). Catecholamines combinations with 2-OHE(2) or 4-OHE(2) enhanced P-UAEC mitogenesis. Catecholestradiol-induced P-UAEC proliferation was also inhibited by propranolol but not phentolamine. β(2)-AR and β(3)-AR antagonists (ICI 118 551and SR 59230A, respectively) abrogated the mitogenic effects of both 2-OHE(2) and 4-OHE(2). Stimulation of β(2)-ARs and β(3)-ARs using formoterol and BRL 37344 dose-dependently stimulated P-UAEC proliferation, which was abrogated by ICI 118 551 and SR 59230A, respectively. Proliferation effects of both catecholamines and catecholestradiols were only observed in P-UAECs (not nonpregnant UAECs) and were mediated via β(2)-ARs and β(3)-ARs. We demonstrate for the first time convergence of the endothelial AR and estrogenic systems in regulating endothelial proliferation, thus providing a distinct evolutionary advantage for modulating uterine perfusion during stressful pregnancies.

Sex, hormones and neuroeffector mechanisms

Incidence and rate of cardiovascular disease differ between men and women across the life span. Although hypertension is more prominent in men than women, there is a group of vasomotor disorders [i.e. Raynaud's disease, postural orthostatic tachycardia syndrome and vasomotor symptoms (hot flashes) of menopause and migraine] with a female predominance. Both sex and hormones interact to modulate neuroeffector mechanisms including integrated regulation of the Sry gene and direct effect of sex steroid hormones on synthesis, release and disposition of monoamine neurotransmitters, and distribution and sensitivity of their receptors in brain areas associated with autonomic control. The interaction of the sex chromosomes and steroids also modulates these effector tissues, that is, the heart, vascular smooth muscle and endothelium. Although involvement of central serotonergic centres has been studied in regard to mood disorders such as depression, their contribution to cardiovascular risk is gaining attention. Studies are needed to further evaluate how hormonal treatments and drugs used to modulate adrenergic and serotonergic activity affect progression and risk for cardiovascular disease in men and women.

Gender and the renin-angiotensin-aldosterone system

Premenopausal women are protected to some extent from cardiovascular and kidney diseases. Because this protection weakens after menopause, sex hormones are believed to play an important role in the pathogenesis of cardiovascular and kidney diseases. The cardiovascular system and the kidneys are regulated by the renin-angiotensin-aldosterone system (RAAS), which in turn, appears to be regulated by sex hormones. In general, oestrogen increases angiotensinogen levels and decreases renin levels, angiotensin-converting enzyme (ACE) activity, AT(1) receptor density, and aldosterone production. Oestrogen also activates counterparts of the RAAS such as natriuretic peptides, AT(2) receptor density, and angiotensinogen (1-7). Progesterone competes with aldosterone for mineralocorticoid receptor. Less is known about androgens, but testosterone seems to increase renin levels and ACE activity. These effects of sex hormones on the RAAS can explain at least some of the gender differences in cardiovascular and kidney diseases.

Seasonal variation in tissue estrogen-2/4-hydroxylases (EH) and in vitro effects of steroids on ovarian EH activity in the catfish Heteropneustes fossilis

A radiometric assay was used to measure microsomal EH activity from tritiated H(2)O formed during the conversion of [2,4 (3)H] estradiol-17β into catecholestrogens in the microsomal fractions of liver, brain and ovary of the catfish Heteropneustes fossilis. The validation data show that enzyme activity increased with incubation time, and substrate and cofactor (NADPH) concentrations, elicited temperature optima of 30-37°C and pH optima of 6.8-7.8. EH activity was strongly NADPH-dependent and in its absence only 13.48% activity was recorded. Liver recorded the highest enzyme activity, followed by brain and ovary. EH activity showed a significant seasonal variation with the peak activity in spawning phase and the lowest activity in resting phase. In the ovary, the follicular layer (theca and granulosa) elicited the highest activity over that of the denuded oocytes. Modulatory effects of steroids on ovarian enzyme activity were further demonstrated. The incubation of postvitellogenic follicles with 1, 10 or 100 nM concentrations of various steroids for 24 h produced varied effects on EH activity. Progesterone and 2-hydroxyestradiol-17β elicited strong suppressive effects on enzyme activity. Estrogens (E(1), E(2) and E(3)) suppressed the activity in a concentration-dependent manner. Among the progestins tested, 17,20α-dihydroxy-4-pregnen-3-one, the isomer of 17,20β-dihydroxy-4-pregnen-3-one (a teleost maturation-inducing steroid) showed the lowest depressing effect. Among androgens, the testosterone metabolite 11-ketotestosterone (functional teleost androgen) showed a high suppressing effect. Corticosteroids elicited low activity with cortisol suppressed the activity at higher concentrations. The study will form a basis to understand the physiological role of catecholestrogens in ovarian functions.

Ovariectomy does not affect the cardiac sympathovagal balance of female SHR but estradiol does

The low incidence of cardiovascular diseases, including hypertension, in premenopausal women has led to the conclusion that ovarian hormones may have a protective effect on the cardiovascular system. We evaluated the effects of ovariectomy and/or estradiol on sympathovagal balance and heart rate variability (HRV) in female spontaneously hypertensive rats (SHR) with tachycardia and compared them to Wistar rats (12 weeks old; N = 8-12). Ovariectomy (OVX) and/or estradiol (10 µg/kg) did not affect basal arterial pressure in either rat strain, but estradiol increased basal heart rate (HR) in OVX SHR (454 ± 18 vs 377 ± 9 bpm). HR changes elicited by methylatropine and propranolol were used to evaluate the sympathovagal balance. Ovariectomy did not affect the cardiac sympathovagal balance of any group, while estradiol increased sympathetic tone in OVX SHR (120 ± 8 vs 56 ± 10 bpm) and sham-operated Wistar rats (57 ± 7 vs 28 ± 4 bpm), and decreased the parasympathetic tone only in OVX SHR (26 ± 7 vs 37 ± 5 bpm). HRV was studied in the frequency domain (Fast Fourier Transformation). Spectra of HR series were examined at low frequency (LF: 0.2-0.75 Hz) and high frequency (HF: 0.75-3 Hz) bands. The power of LF, as well as the LF/HF ratio, was not affected by ovariectomy, but estradiol increased both LF (29 ± 4 vs 18 ± 3 nu in Wistar sham-operated, 26 ± 5 vs 15 ± 3 nu in Wistar OVX, 50 ± 3 vs 38 ± 4 nu in SHR sham-operated, and 51 ± 3 vs 42 ± 3 nu in SHR OVX) and LF/HF (0.48 ± 0.08 vs 0.23 ± 0.03 nu in Wistar sham-operated, 0.41 ± 0.14 vs 0.19 ± 0.05 nu in Wistar OVX, 0.98 ± 0.11 vs 0.63 ± 0.11 nu in SHR sham-operated, and 1.10 ± 0.11 vs 0.78 ± 0.1 nu in SHR OVX). Thus, we suggest that ovariectomy did not affect the cardiac sympathovagal balance of SHR or Wistar rats, while estradiol increased the sympathetic modulation of HR.

Physiology of Kidney Renin

The protease renin is the key enzyme of the renin-angiotensin-aldosterone cascade, which is relevant under both physiological and pathophysiological settings. The kidney is the only organ capable of releasing enzymatically active renin. Although the characteristic juxtaglomerular position is the best known site of renin generation, renin-producing cells in the kidney can vary in number and localization. (Pro)renin gene transcription in these cells is controlled by a number of transcription factors, among which CREB is the best characterized. Pro-renin is stored in vesicles, activated to renin, and then released upon demand. The release of renin is under the control of the cAMP (stimulatory) and Ca2+(inhibitory) signaling pathways. Meanwhile, a great number of intrarenally generated or systemically acting factors have been identified that control the renin secretion directly at the level of renin-producing cells, by activating either of the signaling pathways mentioned above. The broad spectrum of biological actions of (pro)renin is mediated by receptors for (pro)renin, angiotensin II and angiotensin-( 1 – 7 ).

Expression of the IGF and the aromatase/estrogen receptor systems in human adrenal tissues from early infancy to late puberty: implications for the development of adrenarche

Adrenarche is a process of postnatal sexual maturation occurring in higher primates, in which there is an increase in the secretion of adrenal androgens. It is the consequence of a process of postnatal organogenesis characterized by the development of a new zone in the adrenal cortex, the zona reticularis (ZR). The mechanism of this phenomenon remains poorly understood, suggesting that it might be a multifactorial event. A relationship between circulating IGF-I, insulin sensitivity, and adrenal androgens has been postulated. Boys and girls have different patterns of changes in insulin sensitivity at puberty, perhaps secondary to differences in the estrogen milieu. Estrogen effects may also play a role in premature adrenarche. Peripheral or local IGF-1 actions could regulate adrenal progenitor cell proliferation and migration. Since adrenal progenitor cells as well as IGF-I and the IGF-R1 are located in the outer zone of the adrenal cortex during childhood and adolescence, this peripheral cell layer, below the capsule, may contain undifferentiated progenitor cells. Therefore, the IGF-R1 signaling pathway might positively modulate the proliferation and migration of adrenal progenitor cell to stimulate the development of adrenal zones, including ZR. However, no evidence of a direct action of IGF-I on ZR was found. In addition, a role for estrogens in the ontogenesis of ZR is suggested by the presence of aromatase (CYP19) in the subcapsular zona glomerulosa and in the adrenal medulla. Estrogens produced locally could act on ZR by interacting with estrogen receptor beta (ERbeta), but not alpha, and membrane estrogen receptor GPR-30. An estradiol-induced increase in DHEA/cortisol ratio was indeed seen in cultures of adrenocortical cells from post-adrenarche adrenals. In summary, several lines of evidence point to the action of multiple factors, such as local adrenal maturational changes and peripheral metabolic signals, on postnatal human adrenal gland ZR formation.

Sexual dimorphism in the catecholamine-containing thymus microenvironment: a role for gonadal hormones

The study was undertaken to explore whether there were: i) apart from neural and circulatory, some other sources of catecholamines (CAs) in rat thymus and ii) gender-specific differences in thymic CA levels, and if so to elucidate the role of sex steroids in this phenomenon. Tyrosine hydroxylase (TH) immunoreactivity was found in thymocytes and thymic epithelial cells (some of which showed morphological features of nurse cells). The density of CA-synthesizing cells was greater in male than in female rats. Noradrenaline (NA), but not dopamine (DA), was detected in thymocytes. NA and DA levels in thymi, and the NA level in thymocytes, were higher in male rats. To explore the putative role of sex steroids in this dichotomy in the thymi of adult rats gonadectomized (Gx) or sham-Gx at the age of 30 days the density of TH+ cells and CA levels were measured. Gonadectomy abolished sexual dimorphism in the density of thymic TH+ cells (diminishing their density in male rats) and thymic CA levels (the NA levels were reduced in rats of both sexes and also the DA level in male rats). Therefore, it can be assumed that testicular and ovarian hormones control thymic NA and DA levels via different mechanisms. Moreover, in Gx rats, despite the decrease in the overall thymic NA level, an increase in the thymocyte NA level was found indicating that gonadal hormones exert differential effects on the NA level in distinct thymic cellular compartments.

Oestrogens and the structural and functional plasticity of neurons: implications for memory, ageing and neurodegenerative processes

Oestrogens have numerous effects on the brain, beginning during gestation and continuing on into adulthood. Many of these actions involve areas of the brain that are not primarily involved in reproduction, such as the basal forebrain, hippocampus, caudate putamen, midbrain raphe and brainstem locus coeruleus. This paper describes three actions of oestrogens that are especially relevant to brain mechanisms involved in memory processes and their alterations during ageing and neurodegenerative diseases: (1) the regulation of cholinergic neurons by oestradiol in the rat basal forebrain, involving induction of choline acetyltransferase and acetylcholinesterase according to a sexually dimorphic pattern; (2) the regulation of synaptogenesis in the CA1 region of the hippocampus by oestrogens and progestins during the four- to five-day oestrus cycle of the female rat. Formation of new excitatory synapses is induced by oestradiol and involves N-methyl-D-aspartate receptors; removal of these synapses involves intracellular progestin receptors; (3) sex differences in hippocampal structure, which may help to explain differences in the strategies that male and female rats use to solve spatial navigation problems. During the period of development when testosterone is elevated in the male, aromatase and oestrogen receptors are also elevated, making it likely that this pathway is involved in the masculinization of hippocampal structure.

Identification and developmental changes of aromatase and estrogen receptor expression in prepubertal and pubertal human adrenal tissues

CONTEXT

The mechanisms of postnatal adrenal zonation remain unclear.

OBJECTIVE

To provide a clue for a possible role of estrogens in adrenarche, we studied the expression of estrogen receptor (ER)alpha, ERbeta, G protein-coupled receptor (GPR)30, and cP450aromatase (cP450arom) in human adrenal tissue.

DESIGN

Human adrenal tissue was collected from three postnatal age groups (Grs): Gr 1, younger than 3 months (n = 12), fetal zone involution; Gr 2, 3 months to 6 yr (n = 17), pre-adrenarche; and Gr 3, older than 6-20 yr (n = 12), post-adrenarche period.

RESULTS

ERbeta mRNA in Grs 1 and 3 was higher than in Gr 2 (P < 0.05). By immunohistochemistry and laser capture microdissection followed by RT-PCR, ERbeta was expressed in zona reticularis and fetal zone, GPR30 in zona glomerulosa (ZG) and adrenal medulla, while ERalpha mRNA and protein were undetectable. cP450arom mRNA in Gr 3 was higher than in Grs 1 and 2 (P < 0.05), and localized to ZG and adrenal medulla by laser capture microdissection. cP450arom Immunoreactivity was observed in adrenal medulla in the three Grs and in subcapsular ZG of Gr 3. Double-immunofluorescence studies revealed that cP450arom and chromogranin A only colocalize in adrenal medulla of subjects younger than 18 months. In these samples, exon 1.b-derived transcript was 3.5-fold higher, while exon 1.a-, 1.c-, and 1.d-derived transcripts were 3.3-, 1.9-, and 1.7-fold lower, respectively, than in subjects older than 6 yr.

CONCLUSIONS

Our results suggest that estrogens produced locally in adrenal medulla would play a role in zona reticularis functional differentiation through ERbeta. The cP450arom and GPR30 expression in subcapsular ZG, colocalizing with a high-cell proliferation index, previously reported, suggests a local GPR30-dependent estrogen action in proliferation and migration of progenitor adrenal cells.

Estrogen regulation of neurotrophin expression in sympathetic neurons and vascular targets

We hypothesize that estrogen exerts a modulatory effect on sympathetic neurons to reduce neural cardiovascular tone and that these effects are modulated by nerve growth factor (NGF), a neurotrophin that regulates sympathetic neuron survival and maintenance. We examined the effects of estrogen on NGF and tyrosine hydroxylase (TH) protein content in specific vascular targets. Ovariectomized, adult Sprague-Dawley rats were implanted with placebo or 17beta-estradiol (release rate, 0.05 mg/day). Fourteen days later, NGF levels in the superior cervical ganglia (SCG) and its targets, the heart, external carotid artery, and the extracerebral blood vessels, as well as estrogen receptor alpha (ERalpha) content levels in the heart, were determined using semi-quantitative Western blot analysis. TH levels in the SCG and extracerebral blood vessels were determined by Western blotting and immunocytochemistry, respectively. Circulating levels of 17beta-estradiol and prolactin (PRL) were quantified by RIA. Estrogen replacement significantly decreased NGF protein in the SCG and its targets, the external carotid artery, heart and extracerebral blood vessels. TH protein associated with the extracerebral blood vessels was also significantly decreased, but ERalpha levels were significantly increased in the heart following estrogen replacement. These results indicate that estrogen reduces NGF protein content in sympathetic vascular targets, which may lead to decreased sympathetic innervations to these targets, and therefore reduced sympathetic regulation. In addition, the estrogen-induced increase in ERalpha levels in the heart, a target tissue of the SCG, suggests that estrogen may sensitize the heart to further estrogen modulation, and possibly increase vasodilation of the coronary vasculature.

A novel mechanism for adenylyl cyclase inhibition from the crystal structure of its complex with catechol estrogen

Catechol estrogens are steroid metabolites that elicit physiological responses through binding to a variety of cellular targets. We show here that catechol estrogens directly inhibit soluble adenylyl cyclases and the abundant trans-membrane adenylyl cyclases. Catechol estrogen inhibition is non-competitive with respect to the substrate ATP, and we solved the crystal structure of a catechol estrogen bound to a soluble adenylyl cyclase from Spirulina platensis in complex with a substrate analog. The catechol estrogen is bound to a newly identified, conserved hydrophobic patch near the active center but distinct from the ATP-binding cleft. Inhibitor binding leads to a chelating interaction between the catechol estrogen hydroxyl groups and the catalytic magnesium ion, distorting the active site and trapping the enzyme substrate complex in a non-productive conformation. This novel inhibition mechanism likely applies to other adenylyl cyclase inhibitors, and the identified ligand-binding site has important implications for the development of specific adenylyl cyclase inhibitors.

Effect of excitotoxic lesions of the neonatal ventral hippocampus on the immobility response in rats

Rats with neonatal ventral hippocampal (nVH) lesions show postpubertal hypersensitivity to dopamine agonists, which may be reversed by neuroleptic treatment. In addition, the immobility response (IR) may be regulated by dopaminergic activity. We investigated the influence of the IR caused by clamping the neck of rats that had received bilateral ibotenic acid lesions of the ventral hippocampus at postnatal day 7 (PD7). At both ages, prepubertal (PD35) and postpubertal (PD56), the duration of the IR was significantly increased in animals with lesions when compared to controls. These findings indicate that nVH damage results in behavioral changes, such as enhancement of the IR, related to mesolimbic dopaminergic transmission.

Catecholamines block the antimitogenic effect of estradiol on human coronary artery smooth muscle cells

Sequential conversion of estradiol to catecholestradiols and methoxyestradiols by cytochrome-P(450) (CYP450) and catechol-O-methyltransferase (COMT), respectively, contributes to the antimitogenic effects of estradiol on vascular smooth muscle cell (SMC) growth via estrogen receptor-independent mechanisms. Because catecholamines are also substrates for COMT, we hypothesize that catecholamines may abrogate the vasoprotective effects of estradiol by competing for COMT and inhibiting methoxyestradiol formation. To test this hypothesis, we investigated the antimitogenic/inhibitory effects of estradiol on human coronary artery SMC growth (cell number, DNA synthesis, collagen synthesis, and SMC migration) and ERK1/2 phosphorylation in the presence and absence of catecholamines. Norepinephrine, epinephrine, isoproterenol, and OR486 (COMT inhibitor) abrogated the inhibitory effects of estradiol on SMC growth and ERK1/2 phosphorylation. The interaction of catecholamines with estradiol was not affected by phentolamine or propanolol, alpha- and beta-adrenoceptor antagonists, respectively. The antimitogenic effects of 2-hydroxy-estradiol, but not 2-methoxyestradiol, were abrogated by epinephrine, isoproterenol, and OR486. Catecholamines inhibited the conversion of both estradiol and 2-hydroxy-estradiol to 2-methoxyestradiol, and SMCs expressed CYP1A1 and CYP1B1. Our findings suggest that catecholamines within the coronary arteries may abrogate the antivasoocclusive effects of estradiol by blocking the conversion of catecholestradiols to methoxyestradiols. The interaction between catecholamines and estradiol metabolism may importantly define the cardiovascular effects of estradiol therapy in postmenopausal women.

In vitro effects of catecholamines and catecholestrogens on brain tyrosine hydroxylase activity and kinetics in the female catfish Heteropneustes fossilis

Effects of catecholamines and catecholestrogens on tyrosine hydroxylase (TH) activity and kinetics were investigated in the telencephalon and hypothalamus of female Heteropneustes fossilis in gonad quiescent (resting) and recrudescent (preparatory) phases. Dopamine, noradrenaline and adrenaline and the catecholestrogen, 2-hydroxyestradiol-17 beta inhibited TH activity in a concentration-dependent manner in both resting and preparatory phases, with a higher effect in the resting phase. Two- methoxyestradiol-17 beta did not alter TH activity in any season. The catecholamines inhibited TH in a competitive manner increasing apparent K(m) values significantly without altering the apparent V(max). Two-hydroxyestradiol-17 beta inhibited significantly the enzyme in a noncompetitive manner and decreased apparent V(max) without altering apparent K(m) values. The apparent K(i) is higher for dopamine than noradrenaline or adrenaline. The apparent K(i) for 2-hydroxyestradiol-17 beta is not significantly different from that of noradrenaline. The present results suggest an interaction between oestradiol-17beta (E2) and catecholamine metabolism at the level of tyrosine hydroxylation and E2 effects on catecholamines may be mediated through its 2-hydroxylation.

Estrogen effect on heart rate variability in hypertensive postmenopausal women

Healthy postmenopausal women and hypertensive patients show an imbalance in the modulation of autonomic nervous control of the cardiovascular system, which may increase the cardiovascular risk.

OBJECTIVE

To examine the heart rate variability (HRV) response to estrogen replacement therapy (ERT) and its association with changes in metabolic variables in hypertensive postmenopausal women.

METHODS

A double-blind, placebo-controlled clinical trial was conducted in 30 hypertensive postmenopausal women receiving 180 mg/day of verapamil. The experimental group (n=16) received 0.625 mg OD of natural conjugated estrogens during 4 months, while control group (n=14) received a placebo. Lipids, lipoproteins, apolipoproteins, glucose and insulin were measured at 0, 2 and 4 months. HRV was determined in time and frequency domains using a 24-h Holter before and after ERT.

RESULTS

Significant higher values of spectral and non-spectral parameters of HRV, associated with a lower LF/HF ratio, were found at the end of 4 months of ERT. Multiple regression analysis revealed that estrogen treatment itself and changes in total cholesterol, LDL-cholesterol, glucose and waist circumference, contributed to the changes observed in indexes reflecting parasympathetic activity in time and frequency domains.

CONCLUSIONS

We conclude that ERT partially improves HRV favoring increased parasympathetic drive, and that part of the effect may be mediated by changes in metabolic variables.

The effects of transdermal estradiol on the response to mental stress in postmenopausal women: a randomized trial

PURPOSE

Estrogens inhibit adrenomedullary catecholamine release and catecholamine-mediated responses to stress. We examined whether estrogen supplementation reduces the sympathoadrenal response to mental stress in postmenopausal women.

MATERIALS AND METHODS

We compared the effects of 3-week treatment with transdermal 17-beta-estradiol and placebo in 10 postmenopausal women using a randomized, blinded, crossover design. We measured plasma catecholamine levels and the cardiovascular and metabolic responses to a 15-minute stress with mental arithmetic. Treatments were compared using repeated measures analysis of variance.

RESULTS

During placebo treatment, mean (+/- SD) epinephrine levels reached a peak of 431 +/- 135 pmol/liter after 15 minutes of stress; the epinephrine response was blunted during estradiol treatment, with a peak of 357 +/- 77 pmol/liter (P <0.05). Estradiol also blunted the diastolic blood pressure response to stress (baseline levels of 78 +/- 15 mm Hg vs peak of 90 +/- 6 mm Hg during placebo; baseline of 80 +/- 8 mm Hg vs peak of 84 +/- 6 mm Hg during estradiol; P <0.05). Estradiol treatment also blunted the decrease in the standard deviation of the mean of the electrocardiographic RR intervals and the increase in the ratio between the low-frequency and high-frequency bandwidths.

CONCLUSION

We observed a moderate, although significant, reduction in markers of the stress response to mental arithmetic in postmenopausal women treated with transdermal 17-beta-estradiol.

Dioxin-like and non-dioxin-like toxic effects of polychlorinated biphenyls (PCBs): implications for risk assessment

Polychlorinated biphenyls (PCBs) are persistent, bioaccumulative, and toxic contaminants in the environment. Individual PCB congeners exhibit different physicochemical properties and biological activities that result in different environmental distributions and toxicity profiles. The variable composition of PCB residues in environmental matrices and their different mechanisms of toxicity complicate the development of scientifically based regulations for the risk assessment. In this article various approaches for the assessment of risks of PCBs have been critically examined. Recent developments in the toxic equivalency factor (TEF) approach for the assessment of toxic effects due to dioxin-like PCBs have been examined. PCB exposure studies that describe non-dioxin-like toxic effects, particularly neurobehavioral effects and their effective doses in animals were compiled. A comparative assessment of effective doses for dioxin-like and non-dioxin-like effects by PCBs has been made to evaluate the relative significance of non-ortho-and ortho-substituted PCBs in risk assessment. Using mink as an example, relative merits and implications of using TEF and total PCB approaches for assessing the potential for toxic effects in wildlife was examined. There are several advantages and limitations associated with each method used for PCB risk assessment. Toxic effects due to coplanar PCBs occur at relatively smaller concentrations than those due to non-dioxin-like PCBs and therefore the TEF approach derives the risk assessment of PCBs, in the environment. The need for the refinement of TEF approach for more accurate assessment of risks is discussed.

Role of 17beta-estradiol in the modulation of baroreflex sensitivity in male rats

Female mammals have an enhanced baroreflex sensitivity compared with their male counterparts, leading researchers to speculate that estrogen modulates autonomic tone. Therefore, this study tests the hypothesis that exogenous estrogen can enhance the baroreflex sensitivity of male rats. Male Sprague-Dawley rats anesthetized with thiobutabarbitol sodium (50 mg/kg) were instrumented to measure blood pressure and heart rate and for the intravenous injection of drugs. The baroreflex was tested using intravenous injections of phenylephrine (0.025, 0.05, and 0.1 mg/kg), and the cardiovascular responses were plotted to obtain a measure of the sensitivity of the cardiac baroreflex. Intravenous injection of estrogen produced dose-related increases in the baroreflex sensitivity due to an increase in the magnitude of the reflex bradycardia. In a separate group of animals, stimulation of the vagus nerve for 2 h resulted in a decrease in baroreflex sensitivity. This effect was blocked when estrogen (1 x 10(-2) mg/kg) was administered immediately before the end of stimulation. In conclusion, intravenous injection of estrogen in male rats significantly enhanced baroreflex sensitivity and blocked the attenuation in the baroreflex sensitivity observed after vagal stimulation.

Oxidation of 4-alkylphenols and catechols by tyrosinase: ortho-substituents alter the mechanism of quinoid formation

Numerous phenols and catechols are known to be substrates for tyrosinase. While the catalytic mechanism of phenol oxidation by tyrosinase has been well studied, little work has been done to determine the influence of substituents on the reaction. In the present investigation, we explored the effects of changing substituents at the 2 and 6 position on the mechanism of tyrosinase-catalyzed oxidation of 4-allyl and 4-propylphenols and catechols. We have previously demonstrated that tyrosinase initially oxidizes hydroxychavicol (4-allyl-catechol) to an o-quinone (3,5-cyclohexadien-1,2-dione) which because of the relatively acidic protons in the benzyl position, readily isomerizes to the tautomeric p-quinone methide (4-allylidene-2,5-cyclohexadien-1-one, QM) (Bolton et al., 1994). We have confirmed through GSH trapping studies that oxidation of 4-allylphenol by tyrosinase yields the same o-quinone GSH conjugates as hydroxychavicol. In contrast, the presence of additional ortho substituents dramatically alters the mechanism of tyrosinase-catalyzed oxidation of 4-alkylphenols. For example, eugenol (4-allyl-2-methoxyphenol), which possesses 1 ortho-methoxy substituents, is not oxidized to a o-quinone or a QM. However, when both ortho o-quinones or QMs which may be selectively toxic to the malignant melanocyte. Although mammalian tyrosinase is much more substrate specific compared to the mushroom tyrosinase used in this study [42], it should be possible to identify compounds which are substrates for the mammalian form but are otherwise oxidatively stable. In order to develop such target compounds an improved understanding of substituent effects on tyrosinase-catalyzed oxidation of catechols and phenols is necessary. This should for the development of strategies for therapeutic compounds that are selectively toxic toward melanoma.

Epidemiological and laboratory evidence of PCB-induced neurotoxicity

The purpose of this review is to provide a selective, but critical, assessment of important findings derived from both epidemiological and laboratory studies suggesting that: (1) exposure to polychlorinated biphenyls (PCBs) and related halogenated aromatic hydrocarbons induces significant neurological and behavioral dysfunctions in humans and laboratory animals, particularly following exposure during gestation and lactation; (2) the neurochemical actions of PCBs depend on their structure and the developmental status of the animal at the time of exposure; and (3) the mechanisms responsible for these changes may involve alterations in basic cellular signaling processes and endocrine function that influence the synthesis and activity of important central nervous system neurotransmitters, the organization of the developing brain, and the behavioral responses to these environmental contaminants.

Equine cytochrome P450 aromatase exhibits an estrogen 2-hydroxylase activity in vitro

Aromatase (estrogen synthetase) is a steroidogenic enzyme complex which catalyzes the conversion of androgens to estrogens (termed aromatization). This enzyme was purified from adult equine testis to homogeneity by five chromatographic steps. The ability of purified and reconstituted equine aromatase to exhibit an estrogen 2-hydroxylase activity was tested and compared to testosterone aromatization. Enzymatic activities were assessed by tritiated water release from labelled estradiol and testosterone. Kinetic analysis of estradiol 2-hydroxylation showed an apparent K(m) of 23 microM and a V(max) of 18 nmol/min/mg, whereas the values for testosterone aromatization were a K(m) of 15.7 nM and a V(max) of 34.6 pmol/min/mg. A specific antiserum raised against purified testicular equine P450arom and known to inhibit aromatase activity [1] was also found to inhibit the estrogen hydroxylase activity of equine placental microsomes in a dose-dependent manner with an IC50 value of 15 microl serum: 0.5 ml incubate. The estrogen hydroxylase activity was inhibited in a dose-dependent manner by two classes of aromatase inhibitors, i.e. steroidal-- (4-hydroxyandrostenedione and 7alpha-([4-aminophenyl]thio)-androst-4-ene-3, 17-dione)--and non-steroidal--(fadrozole and miconazole). The IC50 values were approximately 300 and 890 nM for 4-hydroxyandrostenedione and 7alpha-([4-aminophenyl]thio)-androst-4-ene-3, 17-dione, and 92 and 285 nM, for fadrozole and miconazole, respectively. Furthermore, 4-hydroxyandrostenedione caused a time-dependent inactivation of estrogen hydroxylase activity. We conclude that equine aromatase is able to use estradiol as a substrate, and converts it to catechol estradiol in vitro, possibly using the active site of aromatization. This is the first demonstration that equine aromatase functions as an estrogen 2-hydroxylase, in addition to transforming androgens into estrogen.

Tyrosine hydroxylase activity and dopamine turnover of rainbow trout (Oncorhynchus mykiss) brain: the special status of the hypothalamus

The dynamics of catecholamine (CA)-synthesis enzymes have been poorly studied in fish. Tyrosine hydroxylase (TH), the rate-limiting enzyme of CA synthesis has been only studied inin vitro conditions. In the present report thein vivo CA synthesis and the CA metabolism were studied in different regions of the forebrain of the rainbow trout. Levels of norepinephrine (NE), dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and the rate of accumulation of 3,4-dihydroxyphenylalanine (DOPA) were determined by HPLC following a treatment with hydroxybenzylhydrazine (NSD), a potential inhibitor of DOPA decarboxylase. Kinetics of the accumulation of DOPA and of the decline of DOPAC were in agreement with those found in rat, evidencing that the accumulation of DOPA following NSD can be used in trout to quantify thein vivo enzymatic activity of tyrosine hydroxylase. Experiments using treatment with NSD or with methyl-p-tyrosine reached a same conclusion: the DA neuronal activity in trout is much higher than NE neuronal activity. However, the hypothalamus had high DA levelsvs. lowin vitro andin vivo TH activities and exhibited a low CA turnover.

Sex and gonadal activity modify the effect of 2-hydroxyestradiol on hypothalamic GABA uptake in the rat

The aim of this study was to determine the changes induced by sex and sexual steroids on the effect of the catecholestrogen 2-hydroxyestradiol (2OHE2) upon hypothalamic GABA uptake. For this purpose we have measured [3H]-GABA uptake by crude synaptosomal fractions obtained from normal female and male rats and from ovariectomized and virilized female rats in the presence or absence of increasing concentrations (0.1 to 100 microM) of 20HE2. The results presented in this paper demonstrate that the effect of the catecholestrogen varied according to sex: it potentiated the specific [3H]-GABA uptake in female rats, whereas it clearly inhibited the uptake in male and virilized rats. The enhancing effect of the catecholestrogen was not affected by ovariectomy, but a higher specific GABA uptake was observed in the ovariectomized animals. The present study provides the first evidence that the effect of 2OHE2 on hypothalamic GABA uptake depends on sex, thus suggesting the existence of a sexual dimorphism. Further studies in this field are required to elucidate the physiological significance and the underlying mechanism of the mentioned effect.

Effect of catecholestrogens on [3H]-GABA uptake by hypothalamic crude synaptosomes

Catecholestrogens (CE), 2-hydroxyestradiol, 2-hydroxyestrone and primary estrogens, estradiol and estrone were tested in their ability to compete for the high affinity uptake of [3H]-GABA into crude synaptosomal fractions. Aliquots of the crude synaptosomal fraction obtained from normal rats were incubated for 10 min at 37 degrees C with [3H]-GABA in the presence, or absence, of estrogens and catecholestrogens. Neither estradiol nor estrone modified the specific [3H]-GABA uptake into crude synaptosomal fractions. On the contrary, CE significantly affected the specific [3H]-GABA uptake in a dose-dependent manner: low concentrations of CE enhanced the uptake; this effect disappeared with high concentrations of the compounds. The stimulatory effect of CE on [3H]-GABA uptake was blocked when samples were coincubated with nipecotic acid, thus suggesting that this effect is specific rather than the result of non-specific interactions of CE with the hypothalamic membrane.

Effects of estrogens on human melanocytes in vitro

Subjects with elevated serum estrogen concentrations, such as those who are pregnant or ingesting estrogen-containing contraceptive medication, may develop increased skin pigmentation. As little information is available on the mechanism(s) underlying this relationship, the in vitro effects of estrogens on melanocytes cultured from normal human skin were examined. Physiological concentrations of 17 beta-estradiol (10(-11) to 10(-9) M) significantly increased the activity of tyrosinase in melanocytes from 15 of 23 subjects. The observed increases ranged from 1.2- to 2.4-fold. Melanin synthesis, which correlated with tyrosinase activity (r = 0.98, P < 0.001) was increased to a similar extent. Melanin extrusion was also increased by 17 beta-estradiol (10(-9) M). The estrogens, estriol (10(-9) M) and estrone (10(-9) M) stimulated tyrosinase activity and melanin extrusion to a lesser extent than 17 beta-estradiol. The analogue 17 alpha-estradiol (10(-9) M) was shown to have effects on melanocyte tyrosinase activity and melanin extrusion that were equivalent to those of 17 beta-estradiol. The pure estrogen antagonist ICI 164384 (10(-6) M) also stimulated tyrosinase activity. Cycloheximide (50 micrograms/ml) inhibited 17 beta-estradiol-induced tyrosinase stimulation (P < 0.001). These results indicate that several aspects of melanocyte function respond directly to estrogenic stimulation. The equivalent effects of the 17 alpha-analogue and a "pure" anti-estrogen suggest that the 17 beta-estradiol response may be mediated through a non-classical mechanism which is similar to that described in other tissues of neural crest origin.

Distribution and regulation of estrogen-2-hydroxylase in the quail brain

The anatomical distribution and endocrine regulation of the estrogen-2-hydroxylase activity were investigated in the brain of adult male and female Japanese quail. Significant levels of enzymatic activity were detected in all brain regions that were studied, but the highest levels were observed in preoptic and hypothalamic brain nuclei that are known to contain high levels of aromatase activity. These data are consistent with previous results suggesting that the placental aromatase is also responsible for the estrogen-2-hydroxylase activity. However, there is a marked sex difference and a control by T of aromatase activity in the quail brain, and no such difference in 2-hydroxylase activity could generally be detected except in the VMN. Further studies will be needed to know whether the previously published conclusions concerning the human placenta also apply to the brain. The present data are consistent with the idea that estrogens formed locally in the brain by testosterone aromatization could affect reproduction by interfering with the catecholaminergic transmission after being metabolized into catechol-estrogens.

Oxidative stress: free radical production in neural degeneration

It is not yet established whether oxidative stress is a major cause of cell death or simply a consequence of an unknown pathogenetic factor. Concerning chronic diseases, as Parkinson's and Alzheimer's disease are assumed to be, it is possible that a gradual impairment of cellular defense mechanisms leads to cell damage because of toxic substances being increasingly formed during normal cellular metabolism. This point of view brings into consideration the possibility that, besides exogenous factors, the pathogenetic process of neurodegeration is triggered by endogenous mechanisms, either by an endogenous toxin or by inherited metabolic disorders, which become progressively more evident with aging. In the following review, we focus on the oxidative stress theory of neurodegeneration, on excitotoxin-induced cell damage and on impairment of mitochondrial function as three major noxae being the most likely causes of cell death either independently or in connection with each other. First, having discussed clinical, pathophysiological, pathological and biochemical features of movement and cognitive disorders, we discuss the common features of these biochemical theories of neurodegeneration separately. Second, we attempt to evaluate possible biochemical links between them and third, we discuss experimental findings that confirm or rule out the involvement of any of these theories in neurodegeneration. Finally, we report some therapeutic strategies evolved from each of these theories.

Catecholamine synthesis in the rainbow trout (Oncorhynchus mykiss) brain: modulation of tyrosine hydroxylase activity

Levels of catecholamines and tyrosine hydroxylase (TH) activity were measured in brain homogenates from female rainbow trout. In triploid fish or in diploid fish in ovarian recrudescence, the patterns of catecholamine content expressed as a function of in vitro TH activity vary in different areas of the brain. Km for the pterin cofactor is lower in the telencephalon than in the hypothalamus. Dopamine (DA) and 2-hydroxyestradiol (20HE2) inhibit TH activity (by competitive and non-competitive interaction respectively).The K1 for DA were different in the telencephalon and the hypothalamus and this could explain the different patterns of catecholamine levels and TH activity for these two structures. 20HE2 inhibits TH activity in vitro; a catechol moiety is required since estradiol (E2) is notinhibitory. However, the exact mechanism of inhibition remains unclear. The rapid effect of 20HE2 cannot explain the previously reported activation of catecholamine synthesis by E2 in vivo.

Sex steroids do not alter sex differences in tyrosine hydroxylase activity of dopaminergic neurons in vitro

In order to distinguish the effects of genetic sex from those of sex hormones on the sexual differentiation of dopaminergic neurons, catecholamine synthesis was studied in gender-specific cultures of embryonic day-14 rat diencephalon. In addition to embryos from normal dams, embryos were used whose mothers had been treated with the estrogen antagonist tamoxifen or the testosterone antagonist cyproterone acetate on days 12 and 13 of gestation. Cultures from embryos of untreated dams were fed daily with a medium containing 17 beta-estradiol or testosterone. After 10 days in vitro, cultures were immunostained for tyrosine hydroxylase and the accumulation of dihydroxyphenylalanine (DOPA) was measured in the presence of the DOPA decarboxylase inhibitor NSD 1015. Rates of DOPA synthesis, unlike the numbers of tyrosine hydroxylase-immunoreactive neurons, were markedly higher in female cultures under all experimental conditions. Treatment of dams with antisteroids prior to removal of the embryos had no influence on these results. Treatment of cultures with both steroids decreased DOPA formation in a dose-dependent manner without altering the sex difference. These results suggest that cultured diencephalic dopaminergic neurons develop sex differences in the activity of tyrosine hydroxylase. This sexual dimorphism is initiated independently on the activity of gonadal steroid hormones. Sex hormones exert an additional modulatory influence on the activity of the enzyme but do not abolish or reverse sex differences. Therefore, the concept of a purely epigenetic mode of sexual differentiation of the mammalian brain needs to be broadened to incorporate other mechanisms, such as the cell-autonomous fulfillment of a sex-specific genetic program.

Gas chromatography/mass spectrometry of catechol estrogens

Catecholestrogens (CCEs), namely 2- or 4-hydroxyestradiol and hydroxyestrone, are highly polar, reactive, and extremely labile estrogen metabolites in many experimental conditions. For these reasons, indirect assay methods mainly have been used. Some experimental evidence suggests that CCEs are synthesized and biologically active mostly in target cells. At this level, unfortunately, the indirect assays cannot be used. We present a method of gas chromatographic/mass spectral (GC/MS) analysis for the identification of individual CCEs; the major fragmentation ions of authentic estrogen standards as trimethylsilylether derivatives, and the MS patterns of the major CCEs, namely, 2-hydroxyestradiol and hydroxyestrone, are included. Few examples of CCEs detected in human breast cancer tissues and in breast cyst fluids are reported. Sample extracts were submitted to reversed-phase, high-performance liquid chromatography (RP-HPLC) and were quantified by "on line" electrochemical (EC) detection; thereafter, either crude extracts or single eluted peaks were submitted to GC/MS, by which detection limits of less than 5 pmol were attained. As expected, the molecular ion was the most relevant molecule in all but one case. On the contrary, the other relative intensities of major fragmentation ions M -15, M -30, M -90, and M -15 + (-90) were unevenly distributed, although represented in the majority of cases. In all cases, the GC/MS of peak fractions, purified by RP-HPLC and UV detection, confirmed the results of liquid chromatographic analysis combined with EC detection. In contrast, GC/MS of crude extracts was not equally satisfactory. Comparison of a liquid chromatography system with EC detection and the GC/MS approach revealed some inconsistency in quantitation of individual CCEs.(ABSTRACT TRUNCATED AT 250 WORDS)

The amino acid substrate of bovine tyrosine hydroxylase

Tyrosine hydroxylase catalyzes the tetrahydropterin-dependent hydroxylation of tyrosine to form 3,4-dihydroxyphenylalanine. Several nonphysiological aromatic amino acids have been examined as inhibitors and substrates for bovine adrenal tyrosine hydroxylase. The Ki values for para-substituted phenylalanines increase as the size of the substituent increases. For each A2 increase in surface area of the substituent, the free energy of binding becomes 50 cal more positive. Replacement of the phenyl ring with a pyridyl ring decreases the affinity about one order of magnitude. A number of these aromatic amino acids are also substrates for the enzyme. The KM values again increase in size with increasing size of the substituent, but the Vmax value is independent of the reactivity of the amino acid. The effect of size on binding is consistent with a tight interaction between the para position region of the substrate and the enzyme. The lack of a change in the Vmax value is consistent with the rate-limiting step in catalysis by bovine tyrosine hydroxylase being formation of the hydroxylating intermediate rather than hydroxylation of the amino acid. These results will be useful in designing mechanism-based inhibitors of catecholamine biosynthesis and establish that the mechanisms of rat and bovine tyrosine hydroxylase do not differ significantly.

Inhibitory actions of acute estradiol treatment on the activity and quantity of tyrosine hydroxylase in the median eminence of ovariectomized rats

Abstract The effects of acute estradiol (E(2)) treatment on both the activity of tyrosine hydroxylase (TH) in the median eminence and the serum level of prolactin (PRL) were investigated. Twelve-day-ovariectomized rats were injected with 17beta-E(2) (25mug sc) at 1100 h and sacrificed hourly from 1200 to 2300 h. TH activity was quantified by measuring the amount of exogenous tyrosine converted to L-DOPA in vitro by aliquots of median eminence homogenates. Serum PRL levels were evaluated by radioimmunoassay. A biphasic response of TH activity to treatment was observed: an immediate decrease occurred-preceding and accompanying a rise in serum PRL-followed by an increase beyond control levels 2 h after the maximal release of PRL. The increase in TH activity could be prevented by the pretreatment of rats with a specific rat PRL antiserum, suggesting it was not due to E(2) per se but rather mediated by the E(2)-induced PRL elevation. To pin-point the process underlying the E(2)-induced decrease in TH activity, we evaluated the kinetic parameters of TH in the median eminence as well as its quantity (by Western blot analysis) in the median eminence and arcuate nucleus. Finally, we used a sensitive dot-blot assay to quantify specific TH messenger ribonucleic acid in the arcuate nucleus. The decrease in TH activity after E(2) treatment paralleled an immediate decrease in the affinity of TH for its pterin cofactor (6-MPH4), while V(max) remained unchanged. A decrease in the amount of TH protein in the arcuate nucleus and median eminence as well as in the TH messenger ribonucleic acid level in the arcuate nucleus was also observed, but the latency of these effects precluded a major involvement in the immediate decline of TH activity. Therefore, when observed separately from those of PRL, E(2) effects on TH in tuberoinfundibular dopaminergic neurons are clearly inhibitory consisting of a 'deactivation' of the enzyme together with a reduction of its synthesis.

Formation and metabolism of catecholestrogens in depressed patients

The evidence that catecholestrogens are formed in the brain and exert behavioral effects in animal models suggest that these steroids might have psychotropic activities. In the present investigation, the formation and metabolism of catecholestrogens were studied in depressed patients. Twenty-four-hr urine samples were collected from 6 male patients (59 +/- 8 years) with endogenous retarded depression (subtype primary, endogenous, and recurrent according to Research Diagnostic Criteria) and from 12 male control subjects (51 +/- 4 years). The patients were treated with the monoamine oxidase inhibitor tranylcypromine (10-40 mg/day for 3-4 weeks). The concentrations of primary estrogens, 4- and 2-hydroxyestrogens and 2-methoxyestrogens, were measured in the urine samples after multiple chromatographic separation steps by radioimmunoassay. In the depressed patients, the excretion rates of 4-hydroxyestrogens were significantly lower than in control subjects. The ratio 2-methoxyestrogens:2-hydroxyestrogens as an index for 2-O-methylation was 3.8 +/- 1.6 in patients and 1.8 +/- 0.7 in controls. The increased methylation and reduced 4-hydroxylation rates of patients were not affected by treatment with tranylcypromine though the psychopathological state was improved by 46%. Therefore, it seemed unlikely that the observed alterations were pathognomonically relevant in these depressed patients. The alterations in the formation and methylation of catecholestrogens show that the depressed patients exhibited remarkable metabolic disturbances. The functional role of these disturbances remains to be clarified.

Changes in ingestive behaviors and body weight following intracranial application of 17 alpha-estradiol

The present experiment was conducted to determine if central implants of 17 alpha-estradiol could influence food intake, water intake, and body weight in ovariectomized rats. A total of fifteen animals were fitted with bilateral guide cannulae in the paraventricular nucleus (PVN) and stimulated unilaterally with cholesterol and 17 alpha-estradiol in each side of the brain. Compared with cholesterol treatment, 17 alpha-estradiol implants in the PVN significantly lowered food intake and body weight but did not affect water intake. These findings indicate that the PVN is a brain region responsive to the effects of 17 alpha-estradiol on feeding behavior, and support the hypothesis that the effects of estrogens on ingestive and reproductive behaviors are organized separately within the brain.

Effects of intrastriatal hormones on the dorsal immobility response in male rats

Previous research has shown that estradiol administered either peripherally or directly into the striatum potentiates the dorsal immobility response (DIR) in ovariectomized female rats. Male rats are even more responsive than females to intrastriatal estradiol, and furthermore respond to the effects of catecholestrogens while females do not. In order to determine whether the heightened effects of estrogens in males are due to conversion to catecholestrogens, castrated male rats were given bilateral intrastriatal implants of moxestrol, which cannot be readily converted to a catecholestrogen, and diethylstilbestrol, which can. To determine whether the effects of intrastriatal estradiol in male rats might be related to the effects of androgens on the striatum, castrated male rats were given bilateral intrastriatal implants of testosterone, which can be aromatized to estrogen, and 5 alpha-dihydrotestosterone, which cannot. The effects of each of the hormones tested were measured against those of cholesterol (an inactive control substance) and 17 beta-estradiol. In each case the DIR was measured four hours after the hormone implant. Both synthetic estrogens and 17 beta-estradiol significantly potentiated the DIR, while neither of the androgens had an effect. Thus, the effects of estradiol, synthetic estrogens and catecholestrogens on the male striatum appear to be due to the estrogenic properties of these hormones.

The effects of intrastriatal hormones on the dorsal immobility response in gonadectomized male and female rats

Previous research has shown that intrastriatal estradiol potentiates the dorsal immobility response in ovariectomized female rats. In order to test whether the gonadal steroid hormones act on the male striatum in the same way, gonadectomized male and female Long-Evans hooded rats were given bilateral intrastriatal implants of 17 beta-estradiol (17 beta-E2), 17-alpha-estradiol (17-alpha-E2), 2-hydroxyestradiol (2-OH-E2), 4-hydroxyestradiol (4-OH-E2), or cholesterol. Four hours after the hormone implant the dorsal immobility response (DIR) was measured. In the ovariectomized females, the DIR was significantly potentiated only by 17 beta-E2 and 17-alpha-E2. In the castrated males, the DIR was significantly potentiated by 17 beta-E2, 17-alpha-E2, 2-OH-E2, and 4-OH-E2. While the DIR durations did not differ between males and females after intrastriatal cholesterol, the males had significantly longer DIR durations after each of the other hormones. These results are discussed in terms of estradiol stereospecificity and the properties of catechol estrogens in male and female rats.

O dealkylation and aliphatic and aromatic hydroxylation of 3-methoxy-17 beta-estradiol by Aspergillus alliaceus

Aspergillus alliaceus UI 315 was examined for its ability to metabolize 3-methoxy-17 beta-estradiol. Preparative-scale incubations with this substrate afforded good yields of 6 beta-hydroxy-17 beta-estradiol, 4-hydroxy-17 beta-estradiol, and 4,6 beta-dihydroxy-17 beta-estradiol, which were identified by high-pressure liquid chromatography, 1H and 13C nuclear magnetic resonance, and high-resolution mass spectrometry.

Catechol-O-methyltransferase in the brain of the male African catfish,Clarias gariepinus; distribution and significance for the metabolism of catecholestrogens and dopamine

Catechol-O-methyltransferase, involved in the methylation of catechol substrates, was localized in the brain of the male African catfish,Clarias gariepinus, by means of a radiometric assay using [Methyl-(3)H]S-adenosylmethionine as methyldonor and catecholestrone as substrate. Fore- and midbrain were divided into eighteen, 500 μm thick, transverse sections. With a hollow needle (diameter 1 mm), specific areas of the brain were punched out and assayed. The catechol-O-methyltransferase activity was calculated from the amount of radioactive methoxyestrone formed from catecholestrone and expressed in pmol.mg(-1) tissue.h(-1).The enzyme could be demonstrated throughout the brain. Although the enzyme activity did not differ very much between the various brain regions (max. 15.4; min. 7.5 pmol), there were some areas in the brain with a more than average activity,i.e., the lateral telencephalon (10.3 pmol), the nucleus preopticus (13.1 pmol), nucleus lateralis tuberis (11.0 pmol) and nucleus recessus posterioris (12.0 pmol) of the diencephalon, the tectum opticum (15.4 pmol) and torus semicircularis (13.6 pmol) of the mesencephalon, and the caudal cerebellum of the metencephalon (10.8 pmol). The lowest activity was detected in the caudal metencephalon (7.5 pmol).The presence of the enzyme catechol-O-methyltransferase in the brain of the African catfish and the observation that both catecholestrogens and dopamine can be methylated by this enzyme suggest that catecholestrogens can influence the methylation (inactivation) of dopamine. Incubations of forebrain homogenates with dopamine and catecholestrone or catecholestradiol confirmed that both catecholestrogens can inhibit the methylation of dopamine. Lineweaver-burk plots with various concentrations of the catecholestrogens indicated that the inhibition is competitive. Dixon plots from the inhibition studies gave inhibition constants of 1.4 and 0.6 μM for catecholestrone and catecholestradiol, respectively, indicating that catecholestradiol is a two times stronger inhibitor than catecholestrone.The significance of the inhibition of the methylation of dopamine by the catecholestrogens in the brain is discussed in the light of the negative feedback of gonadal steroids on the central regulation of reproductive processes.

Opposite effects of estrogen and catecholestrogen on hormone-sensitive breast cancer cell growth and differentiation

Catecholestrogens and especially 2-hydroxyestrone (2OH-E1) are estradiol metabolites locally formed in breast cancer cells. The present study demonstrates that the two parent compounds, estradiol (E2) and its metabolite 2OH-E1, exert opposite effects on hormone-sensitive breast cancer cell growth assessed by cell counts and transferrin receptor levels, and also on cell differentiation assessed by secreted proteins such as alpha-lactalbumin and gross cystic disease fluid protein (GCDFP-15). The present findings may highlight estradiol regulation in hormone-sensitive breast cancer cells.