Possible role of Ca2+ channels in the vasodilating effect of 5beta-dihydrotestosterone in rat aorta

Calcium signaling in endothelial and vascular smooth muscle cells: sex differences and the influence of estrogens and androgens

Calcium signaling in vascular endothelial cells (ECs) and smooth muscle cells (VSMCs) is essential for the regulation of vascular tone. However, the changes to intracellular Ca2+ concentrations are often influenced by sex differences. Furthermore, a large body of evidence shows that sex hormone imbalance leads to dysregulation of Ca2+ signaling and this is a key factor in the pathogenesis of cardiovascular diseases. In this review, the effects of estrogens and androgens on vascular calcium-handling proteins are discussed, with emphasis on the associated genomic or nongenomic molecular mechanisms. The experimental models from which data were collected were also considered. The review highlights 1) in female ECs, transient receptor potential vanilloid 4 (TRPV4) and mitochondrial Ca2+ uniporter (MCU) enhance Ca2+-dependent nitric oxide (NO) generation. In males, only transient receptor potential canonical 3 (TRPC3) plays a fundamental role in this effect. 2) Female VSMCs have lower cytosolic Ca2+ levels than males due to differences in the activity and expression of stromal interaction molecule 1 (STIM1), calcium release-activated calcium modulator 1 (Orai1), calcium voltage-gated channel subunit-α1C (CaV1.2), Na+-K+-2Cl- symporter (NKCC1), and the Na+/K+-ATPase. 3) When compared with androgens, the influence of estrogens on Ca2+ homeostasis, vascular tone, and incidence of vascular disease is better documented. 4) Many studies use supraphysiological concentrations of sex hormones, which may limit the physiological relevance of outcomes. 5) Sex-dependent differences in Ca2+ signaling mean both sexes ought to be included in experimental design.

Androgens and Non-Genomic vascular responses in hypertension

Arterial hypertension is a global public health concern. In the last few years, the interest in androgen deficiency has been growing, and the association between androgens and high blood pressure (BP) is still controversial. One purpose of this review was to summarize the available findings in order to clarify whether male sex steroid hormones have beneficial or harmful effect on BP. The second purpose was to enhance the recognition of the acute non-genomic sex-independent vasorelaxing effect of androgens. Remarkably, BP variation is expected to be a consequence of the androgen-induced vasorelaxation which reduces systemic BP; hence the in vivo vasodepressor, hypotensive, and antihypertensive responses of androgens were also analyzed. This article reviews the current understanding of the physiological regulation of vascular smooth muscle contractility by androgens. Additionally, it summarizes older and more recent data on androgens, and some of the possible underlying mechanisms of relaxation, structural-functional differences in the androgen molecules, and their designing ability to induce vasorelaxation. The clinical relevance of these findings in terms of designing future therapeutics mainly the 5-reduced metabolite of testosterone, 5β-dihydrotestosterone, is also highlighted. Literature collected through a PubMed database search, as well as our experimental work, was used for the present review.

Vascular mechanisms of testosterone: The non-genomic point of view

Testosterone (T) is the predominant endogenous androgen in the bloodstream. At the vascular level, T presents genomic and non-genomic effects, and both effects may overlap. The genomic actions assume that androgens can freely cross the plasma membrane of target cells and bind to nuclear androgen receptors, inducing gene transcription and protein synthesis. The non-genomic effects have a more rapid onset and may be related to the interaction with protein/receptor/ion channels of the plasma membrane. The key T effect at the vascular level is vasorelaxation, which is primarily due to its rapid effect. Thus, the main purpose of this review is to discuss the T non-genomic effects at the vascular level and the molecular pathways involved in its vasodilator effect observed in in vivo and in vitro studies. In this sense, the nuclear receptor activation, the influence of vascular endothelium and the activation or inhibition of ion channels (potassium and calcium channels, respectively) will be reviewed regarding all the data that corroborated or not. Moreover, this review also provides a brief update on the association of T with the risk factors for cardiovascular diseases, namely metabolic syndrome, type 2 diabetes mellitus, obesity, atherosclerosis, dyslipidaemia, and hypertension. In summary, in this paper we consider the non-genomic vascular mode of action of androgen in physiological conditions and the main risk factors for cardiovascular diseases.

Androgens are effective bronchodilators with anti-inflammatory properties: A potential alternative for asthma therapy

Changes in plasma androgen levels in asthmatic men may be linked to asthma severity, seemingly acting through nongenomic and genomic effects. Nongenomic effects include rapid relaxation of carbachol or antigenic challenge pre-contracted guinea pig airway smooth muscle (ASM) in vitro: testosterone (TES) blocks l-type voltage dependent Ca²⁺ channels, stored operated Ca²⁺ channels, inositol 1,4,5-trisphosphate receptors and promotes prostaglandin E₂ biosynthesis. In ASM at rest, TES lowers basal intracellular Ca²⁺ concentration and tension, maintaining a proper airway patency keeping steady smooth muscle tension and basal intracellular Ca²⁺ concentration at rest. Moreover, the bronchospasm in sensitized guinea-pigs was ablated by dehydroepiandrosterone (DHEA), a precursor of steroids, TES and its metabolites 5α- and 5β-dihydrotestosterone (DHT). On the other hand, genomic effects related to androgens' anti-inflammatory properties in asthma have been recently studied. Briefly, TES negatively regulates type 2 immune response sustained by CD4+ Th2 and group 2 innate lymphoid cells, diminishing allergic airway inflammation in males. Also, novel findings establish that TES decreases interleukin (IL)-17A protein expression produced by CD4+ Th17 cells and therefore neutrophilic airway inflammation. Clearly, DHEA, TES or its 5β-reduced metabolite that possesses minimal androgenic effect, might have potential therapeutic capacities in the treatment of severe asthma via mechanisms distinct from corticosteroid treatment.

Hypotestosteronemia is an important factor for the development of hypertension: elevated blood pressure in orchidectomized conscious rats is reversed by different androgens

PURPOSE

Hypotestosteronemia is an aging-associated disease. Little is known about experimental evidence linking androgen deficiency to hypertension. Various androgens are acute vasodilators, both in vitro and in vivo. We aimed to systematically investigate blood pressure (BP) in male normotensive intact or orchidectomized (ORX) Wistar and Wistar-Kyoto rats. Furthermore, we studied the acute antihypertensive responses of testosterone (TES), its precursor (DHEA), or its 5β-reduced metabolite (5β-DHT) in conscious, unrestrained, hypertensive Wistar rats caused by orchidectomy to determine their potency and efficacy. Similarly, the mechanism of their action mediated by nitric oxide (NO) was studied in vivo.

METHODS

BP of ORX rats was evaluated weekly for 18 weeks by tail cuff plethysmography. Subsequently, BP of ORX Wistar rats was measured by chronic indwelling vascular catheters, arterial, and venous catheters were implanted under anesthesia for BP recording and androgen administration, respectively. Then, a dose-response curve of each androgen was performed. Likewise, the dose-response curve of 5β-DHT, the most potent androgen, was repeated in the presence of a nonselective NO synthase inhibitor (L-NAME) or an inhibitor of endothelial NO synthesis (Endothelin-1).

RESULTS

ORX rats progressively increased systolic/diastolic BP (167 ± 2.8/141 ± 3.3 mmHg) over 18 weeks. No difference was found between strains. The BP was reduced in a dose-dependent manner caused by i.v. bolus injection of each androgen, with a rank order of potency of: 5β-DHT = DHEA>>TES. Dose-dependent antihypertension induced by 5β-DHT in ORX rats was not abolished in the presence of L-NAME or Endothelin-1.

CONCLUSIONS

These in vivo experimental findings reveal that hypotestosteronemia is a determining factor for the development of hypertension which is powerfully reduced by androgen administration, and 5β-DHT induces a potent and effective antihypertensive response by a NO-independent mechanism.

Vasoactive androgens: Vasorelaxing effects and their potential regulation of blood pressure

BACKGROUND

Testosterone, 5α- and 5β-dihydrotestosterone (-DHT) induce an acute in vitro vasorelaxation and in vivo vasodepressor, hypotensive and antihypertensive responses. Our aim was to study whether androgen-induced blood pressure (BP) reduction is involved with a blockade of Ca²⁺ influx through L-type voltage-operated calcium channels (L-VOCCs) and/or the signaling pathways of α₁-adrenoceptors to induce vasoconstriction, which are one of the major mechanisms of BP maintenance.

MATERIALS AND METHODS

The relaxing potency and efficacy of each androgen in large conduit (thoracic aorta) and resistance (mesenteric) arteries from male hypertensive (SHR) and normotensive (WKY) rats were established. Blood vessels were isometrically recorded and precontracted with KCl or phenylephrine (Phe).

RESULTS

Androgens induced concentration-dependent vasorelaxation in precontracted arteries from SHR and WKY rats. 5β-DHT was always the most potent vasorelaxant in arteries from SHR. The KCl-induced contraction resulted significantly more sensitive to androgen-induced vasorelaxation than the Phe-induced contraction. On Phe-induced contraction, 5β-DHT was more potent in the mesenteric artery than in the thoracic aorta.

CONCLUSIONS

The vasorelaxation induced by androgens is mainly mediated by blocking L-VOCCs and in lesser extent by the blockade of multiple signaling pathways operative during α-adrenoceptor-induced vasoconstriction. 5β-DHT regulates vascular resistance and BP by mainly acting in the mesenteric arterial bed, which may explain its outstanding antihypertensive response previously reported.

Antihypertensive responses of vasoactive androgens in an in vivo experimental model of preeclampsia

Dehydroepiandrosterone (DHEA), testosterone (TES) and its 5-reduced metabolites induce a nongenomic vasorelaxation in several vascular beds of mammals; similarly these hormones produce systemic hypotensive and antihypertensive responses in normotensive and hypertensive male rats. Thus, it was hypothesized that the antihypertensive response of androgens, whose levels are elevated during gestation, protect against gestational hypertension. An animal model of preeclampsia was induced in female Wistar rats using DOCA-salt-treated pregnant (PT) and normal pregnant (NP) rats. In vivo experiments in conscious rats revealed that bolus intravenous injections of DHEA, TES, 5α- or 5β-dihydrotestosterone (-DHT) log -1.0 to 2.0μmolk^-1min^-1, produced substantial transient reductions in arterial blood pressure (BP), without significant changes in heart rate (HR). Mean arterial blood pressure (MAP) was reduced significantly in both groups. PT rats were more sensitive to the antihypertensive responses of androgens than NP. DHEA and 5β-DHT were the most potent to reduce MAP: 66±07 and 69±2.0mmHg in PT but only 33±0.5 and 35±1.2mmHg in NP rats, respectively. In isolated aortas of PT and NP, the concentration-response curves to each androgen (0.1-100μM) indicated that KCl-induced pre-contraction is more sensitive to all androgens than phenylephrine (Phe) pre-contractions. Notably, 5β-DHT is the greatest vasorelaxant with KCl-induced contraction than with Phe contraction of both groups, suggesting a preferential blockade on L-VOCCs. TES exhibited minor vasorelaxing effect of aortas pre-contracted with KCl, compared to its precursor DHEA and its 5-reduced metabolites. These data show that these androgens exert acute vasorelaxing effects in vitro and remarkably, reduce the BP in vivo in PT and NP at term pregnancy. Moreover, a deficit in feto-placental androgen production during pregnancy may trigger the development of preeclampsia or gestational hypertension.

Antihypertensive effects of androgens in conscious, spontaneously hypertensive rats

Androgens are vasoactive steroids that induce acute vasodilation in a number of isolated vascular beds from different species, but the effects of these hormones on systemic blood pressure (BP) have been studied little. Although it has been reported that androgens exert systemic hypotensive effects through peripheral vasodilation in normotensive rats, there have not been any reports of systemic hypotensive effects of androgens in animals with hypertension. This study was designed to evaluate the acute effects of testosterone (TES) and its 5-reduced metabolites on systemic BP in hypertensive rats and to test the hypothesis that hypotestosteronemia may be involved in the pathogenesis of hypertension. Chronic, indwelling catheters were implanted in carotid artery and jugular vein of 18-21-week-old male spontaneously hypertensive rats (SHR) and normotensive-control Wistar-Kyoto (WKY) rats, for BP recording and drug administration, respectively. Bolus injections of TES, 5α- or 5β-dihydrotestosterone (5α- and 5β-DHT), were administrated cumulatively to conscious rats at doses of 0.1-100μmolkg^-1min^-1. 5β-DHT was also administrated during the pressor effect of Bay K 8644, an L-type voltage-operated Ca²⁺ channel (L-VOCC) agonist. In separate experiments, BP of orchidectomized normotensive male WKY and Wistar rats, with or without androgen-replacement therapy, was evaluated weekly for 10 weeks by tail-cuff plethysmography. TES and its metabolites reduced BP in a dose-dependent manner, while heart rate was reduced with some androgens at the highest doses. The hypotensive effects of androgens were markedly greater in SHR, with a rank order potency of: 5β-DHT>TES>5α-DHT. 5β-DHT, the most potent antihypertensive androgen, abolished the pressor response to Bay K 8644 in SHR. TES deprivation by orchidectomy increased BP in normotensive WKY and Wistar rats, but this hypertension was prevented by TES replacement therapy. BP responses to androgens are androgen structure-dependent. These data indicate that: 1) androgens play a significant role in the control of BP and may contribute to the pathogenesis of hypertension; 2) blockade of L-VOCC is involved in the antihypertensive effects of androgens, which are non-genomically mediated; and 3) hypotestosteronemia may be a risk factor for hypertension.

Androgen deprivation therapy and cardiovascular disease: what is the linking mechanism?

The past decade has brought increased awareness of the potential adverse effects of androgen deprivation therapy (ADT) in men with prostate cancer. Arguably the most important and controversial of these is the increased risk of cardiovascular morbidity and mortality. Although multiple observational studies have shown that men treated with ADT are at increased risk of developing atherosclerotic cardiovascular disease, our understanding of the biological mechanisms that might underlie this phenomenon is still evolving. In this review, we discuss some of the mechanisms that have been proposed to date, including ADT-induced metabolic changes that promote the development and progression of atherosclerotic plaques as well as direct local effects of hormonal factors on plaque growth, rupture and thrombosis.

Systemic hypotensive effects of testosterone are androgen structure-specific and neuronal nitric oxide synthase-dependent

Testosterone (TES) and other androgens exert a direct vasorelaxing action on the vasculature in vitro that is structurally specific and independent of cytosolic androgen receptor (AR). The effects of intravenous androgen infusions on mean arterial blood pressure (BP) and heart rate (HR) were determined in conscious, unrestrained, chronically catheterized, ganglionically blocked (hexamethonium, HEX; 30 mg/kg ip) male Sprague-Dawley (SD) and testicular-feminized male (Tfm; AR-deficient) rats, 16-20 wk of age. BP and HR were recorded at baseline and with increasing doses of androgens (0.375-6.00 μmol·kg(-1)·min(-1) iv; 10 min/dose). Data are expressed as means ± SE (n = 5-8 rats/group). In SD rats, baseline BP and HR averaged 103 ± 4 mmHg and 353 ± 12 beats/min (bpm). TES produced a dose-dependent reduction in BP to a low of 87 ± 4 mmHg (Δ16%), while HR was unchanged (354 ± 14 bpm). Neither BP (109 ± 3 mmHg) nor HR (395 ± 13 bpm) were altered by vehicle (10% EtOH in 0.9% saline; 0.15 ml·kg(-1)·min(-1), iv). In Tfm, TES produced a similar reduction in BP (99 ± 3 to 86 ± 3 mmHg, Δ13%); HR was unchanged (369 ± 18 bpm). In SD, 5β-dihydrotestosterone (genomically inactive metabolite) produced a greater reduction in BP than TES (102 ± 2 to 79 ± 2 mmHg, Δ23%); HR was unchanged (361 ± 9). A 20-μg iv bolus of sodium nitroprusside in both SD and Tfm rats reduced BP 30-40 mmHg, while HR was unchanged, confirming blockade by HEX. Pretreatment of SD rats with neuronal nitric oxide synthase (nNOS) inhibitor (S-methyl-thiocitrulline, SMTC; 20 μg·kg(-1)·min(-1) × 30 min) abolished the hypotensive effects of TES infusion on BP (104 ± 2 vs. 101 ± 2 mmHg) and HR (326 ± 11 vs. 324 ± 8 bpm). These data suggest the systemic hypotensive effect of TES and other androgens involves a direct vasodilatory action on the peripheral vasculature which, like the effect observed in isolated arteries, is structurally specific and AR-independent, and involves activation of nNOS.

Dehydroepiandrosterone, its metabolites and ion channels

This review is focused on the physiological and pathophysiological relevance of steroids influencing the activities of the central and peripheral nervous systems with regard to their concentrations in body fluids and tissues in various stages of human life like the fetal development or pregnancy. The data summarized in this review shows that DHEA and its unconjugated and sulfated metabolites are physiologically and pathophysiologically relevant in modulating numerous ion channels and participate in vital functions of the human organism. DHEA and its unconjugated and sulfated metabolites including 5α/β-reduced androstane steroids participate in various physiological and pathophysiological processes like the management of GnRH cyclic release, regulation of glandular and neurotransmitter secretions, maintenance of glucose homeostasis on one hand and insulin insensitivity on the other hand, control of skeletal muscle and smooth muscle activities including vasoregulation, promotion of tolerance to ischemia and other neuroprotective effects. In respect of prevalence of steroid sulfates over unconjugated steroids in the periphery and the opposite situation in the CNS, the sulfated androgens and androgen metabolites reach relevance in peripheral organs. The unconjugated androgens and estrogens are relevant in periphery and so much the more in the CNS due to higher concentrations of most unconjugated steroids in the CNS tissues than in circulation and peripheral organs. This article is part of a Special Issue entitled "Essential role of DHEA".

Attenuation of cerebral vasospasm and secondary injury by testosterone following experimental subarachnoid hemorrhage in rabbit

BACKGROUND

The vasodilatator effects of testosterone have been widely studied and demonstrated. Based on previous studies of these vasodilatatory activities, we hypothesized that testosterone might have potential effects on subarachnoid hemorrhage-induced cerebral vasospasm.

METHODS

Thirty-two adult male New Zealand white rabbits were randomly divided into four groups of eight rabbits in each group: group 1 (control); group 2 (subarachnoid hemorrhage); group 3 (subarachnoid hemorrhage + vehicle); and group 4 (subarachnoid hemorrhage + testosterone). Testosterone (15 mg/kg, intraperitoneally) was administered 5 min after the intracisternal blood injection and continued for 72 h once per day in the same dose for group 4. Animals were killed 72 h after subarachnoid hemorrhage. Basilar artery cross-sectional areas, arterial wall thicknesses, and hippocampal degeneration scores were evaluated in all groups.

RESULTS

Intraperitoneal administration of testosterone was found to attenuate cerebral vasospasm and provide neuroprotection after subarachnoid hemorrhage in rabbits. Testosterone treatment was determined to be effective at increasing the luminal area and reducing the wall thickness of the basilar artery.

CONCLUSIONS

Our findings show that testosterone has some preventive effects on SAH-induced vasospasm and secondary neuronal injury in rabbits. We propose that the vasodilatatory activity of testosterone is due to its effects on inhibiting calcium channels, activating potassium channels, augmenting nitric oxide synthesis, and inhibiting oxidant stress and inflammation.

SHBG is an important factor in stemness induction of cells by DHT in vitro and associated with poor clinical features of prostate carcinomas

Androgen plays a vital role in prostate cancer development. However, it is not clear whether androgens influence stem-like properties of prostate cancer, a feature important for prostate cancer progression. In this study, we show that upon DHT treatment in vitro, prostate cancer cell lines LNCaP and PC-3 were revealed with higher clonogenic potential and higher expression levels of stemness related factors CD44, CD90, Oct3/4 and Nanog. Moreover, sex hormone binding globulin (SHBG) was also simultaneously upregulated in these cells. When the SHBG gene was blocked by SHBG siRNA knock-down, the induction of Oct3/4, Nanog, CD44 and CD90 by DHT was also correspondingly blocked in these cells. Immunohistochemical evaluation of clinical samples disclosed weakly positive, and areas negative for SHBG expression in the benign prostate tissues, while most of the prostate carcinomas were strongly positive for SHBG. In addition, higher levels of SHBG expression were significantly associated with higher Gleason score, more seminal vesicle invasions and lymph node metastases. Collectively, our results show a role of SHBG in upregulating stemness of prostate cancer cells upon DHT exposure in vitro, and SHBG expression in prostate cancer samples is significantly associated with poor clinicopathological features, indicating a role of SHBG in prostate cancer progression.

Testosterone: a vascular hormone in health and disease

Coronary heart disease is a leading cause of premature death in men. Epidemiological studies have shown a high prevalence of low serum testosterone levels in men with cardiovascular disease (CVD). Furthermore, a low testosterone level is associated in some but not in all observational studies with an increase in cardiovascular events and mortality. Testosterone has beneficial effects on several cardiovascular risk factors, which include cholesterol, endothelial dysfunction and inflammation: key mediators of atherosclerosis. A bidirectional relationship between low endogenous testosterone levels and concurrent illness complicates attempts to validate causality in this association and potential mechanistic actions are complex. Testosterone is a vasoactive hormone that predominantly has vasodilatory actions on several vascular beds, although some studies have reported conflicting effects. In clinical studies, acute and chronic testosterone administration increases coronary artery diameter and flow, improves cardiac ischaemia and symptoms in men with chronic stable angina and reduces peripheral vascular resistance in chronic heart failure. Although the mechanism of the action of testosterone on vascular tone in vivo is not understood, laboratory research has found that testosterone is an L-calcium channel blocker and induces potassium channel activation in vascular smooth muscle cells. Animal studies have consistently demonstrated that testosterone is atheroprotective, whereas testosterone deficiency promotes the early stages of atherogenesis. The translational effects of testosterone between in vitro animal and human studies, some of which have conflicting effects, will be discussed in this review. We review the evidence for a role of testosterone in vascular health, its therapeutic potential and safety in hypogonadal men with CVD, and some of the possible underlying mechanisms.

Mechanisms involved in testosterone-induced relaxation to the pig urinary bladder neck

OBJECTIVES

Testosterone replacement therapy improves bladder capacity in urinary tract dysfunction. There is no information, however, about the role of this steroid hormone on the muscle tension of the bladder outflow region. The current study investigated the mechanisms underlying the testosterone-induced action in the pig bladder neck.

METHODS

Urothelium-denuded bladder neck strips were mounted in myographs for isometric force recordings and for simultaneous measurements of intracellular Ca(2+) concentration ([Ca(2+)](i)) and tension. The relaxations to testosterone, the non-aromatizable metabolite 4,5α-dihydrotestosterone (DHT) and electrical field stimulation (EFS) were carried out on phenylephrine (PhE)-precontracted strips.

RESULTS

Testosterone and DHT evoked similar concentration-dependent relaxations only at very high pharmacological concentrations. The presence of the urothelium and the inhibition of intracellular androgenic receptor (AR), aromatase, 5α-reductase, nitric oxide (NO) synthase, guanylyl cyclase, cyclooxygenase (COX), large-, intermediate- and small-Ca(2+)-activated K(+) channels or ATP-dependent K(+) channels failed to modify the testosterone relaxations. Neuronal voltage-gated Ca(2+) (VOC) channels and voltage-gated K(+) (K(V)) channel blockers potentiated these responses. EFS evoked frequency-dependent relaxations, which were not changed by threshold concentrations of testosterone. In Ca(2+)-free potassium rich physiological saline solution, testosterone inhibited the contractions induced by CaCl(2) and the L-type VOC channel activator (±)-BAY K 8644. Relaxations elicited by testosterone were accompanied by simultaneous decreases in smooth muscle [Ca(2+)](i).

CONCLUSIONS

Testosterone produces relaxation of the pig urinary bladder neck through mechanisms independent of urothelium, AR, aromatase, 5α-reductase, NO synthase, guanylyl cyclase, COX and K(+) channels. Testosterone-induced relaxation is produced via the inhibition of the extracellular Ca(2+) entry through L-type VOC channels.

Regional differences in the vasorelaxing effects of testosterone and its 5-reduced metabolites in the canine vasculature

Although the vasorelaxing effects of testosterone (T) and various androgen metabolites have been observed in a variety of blood vessels and species, previous studies have not systematically compared the vasorelaxing effects of androgen metabolites in different vascular beds within the same species. Therefore, we studied the vasorelaxing effects of T and its 5-reduced metabolites (5α- and 5β-DHT) on KCl-induced contractions of the canine left coronary artery, femoral artery and saphenous vein, using standard isometric recordings. KCl contractions were inhibited by each androgen in a concentration-dependent manner from 1.8 to 310μM. Vascular sensitivity and efficacy were expressed as inhibitory concentration 50 (IC₅₀) and maximal relaxation (R(max)), respectively. The coronary artery was significantly more sensitive to androgen-induced vasorelaxation than the saphenous vein or femoral artery. These vasorelaxing responses were unaffected by an antiandrogen (Flutamide) or the sulfhydryl reagent, N-ethylmaleimide, suggesting a nongenomic mechanism independent of signaling mediated by the androgen receptor or G proteins. Concentration-response curves were unchanged in endothelium-denuded preparations; thus, the endothelium appears to have no role in androgen-induced vasorelaxation. 5β-DHT was the most potent androgen in both coronary and femoral artery, but all three androgens were equipotent in the saphenous vein. It is concluded that: 1) significant regional differences exist in vasorelaxing effects of androgen metabolites in the canine vasculature; 2) structural differences in these androgens determine their vasorelaxing efficacy; and 3) regional differences in androgen-induced vasorelaxation may account for some of the conflicting findings reported on the vasorelaxing effects of the androgens.

Testosterone-induced relaxation of coronary arteries: activation of BKCa channels via the cGMP-dependent protein kinase

Androgens are reported to have both beneficial and detrimental effects on human cardiovascular health. The aim of this study was to characterize nongenomic signaling mechanisms in coronary artery smooth muscle (CASM) and define the ionic basis of testosterone (TES) action. TES-induced relaxation of endothelium-denuded porcine coronary arteries was nearly abolished by 20 nM iberiotoxin, a highly specific inhibitor of large-conductance, calcium-activated potassium (BK(Ca)) channels. Molecular patch-clamp studies confirmed that nanomolar concentrations of TES stimulated BK(Ca) channel activity by ∼100-fold and that inhibition of nitric oxide synthase (NOS) activity by N(G)-monomethyl-L-arginine nearly abolished this effect. Inhibition of nitric oxide (NO) synthesis or guanylyl cyclase activity also attenuated TES-induced coronary artery relaxation but did not alter relaxation due to 8-bromo-cGMP. Furthermore, we detected TES-stimulated NO production in porcine coronary arteries and in human CASM cells via stimulation of the type 1 neuronal NOS isoform. Inhibition of the cGMP-dependent protein kinase (PKG) attenuated TES-stimulated BK(Ca) channel activity, and direct assay determined that TES increased activity of PKG in a concentration-dependent fashion. Last, the stimulatory effect of TES on BK(Ca) channel activity was mimicked by addition of purified PKG to the cytoplasmic surface of a cell-free membrane patch from CASM myocytes (∼100-fold increase). These findings indicate that TES-induced relaxation of endothelium-denuded coronary arteries is mediated, at least in part, by enhanced NO production, leading to cGMP synthesis and PKG activation, which, in turn, opens BK(Ca) channels. These findings provide a molecular mechanism that could help explain why androgens have been reported to relax coronary arteries and relieve angina pectoris.

PKG is involved in testosterone-induced vasorelaxation of human umbilical artery

The cyclic nucleotides involvement in the vasorelaxation induced by testosterone in human umbilical artery was investigated. The effect of this hormone on denuded human umbilical arteries contracted by serotonin (5-HT), histamine or KCl was analysed. Testosterone effect on potassium current (IK) was also studied in human umbilical artery vascular smooth muscle cells (HUASMC). In general, the relaxant effects of testosterone, sodium nitroprusside (SNP) and atrial natriuretic peptide (ANP) are similar. The testosterone relaxant effect is not different to the induced by the conjoint application of ANP and testosterone. However, the effects of SNP and testosterone seem additive. The inhibition of protein kinase A (PKA) did not modify the testosterone relaxant effect, but protein kinase G (PKG) inhibition significantly reduced the testosterone effect independently of the contractile stimuli. In HUASMC, the IK is mainly constituted by potassium exit through voltage sensitive (KV) and large-conductance Ca2+ activated (BKCa) potassium channels. Testosterone significantly activates the basal IK. SNP does not induce a significant modification in basal or testosterone stimulated IK. In contrast, ANP stimulates the basal IK, but does not increase the testosterone stimulation on IK. The IK increases induced by testosterone or by ANP are not significantly affected by the PKA inhibition, but are completely inhibited by the PKG inhibition. Our results show that testosterone and ANP stimulate the activity of BKCa and KV channels due to PKG activation and suggest that this hormone relaxes by activating particulate guanylate cyclase which increases the cGMP intracellular level.

Testosterone and cholesterol vasodilation of rat aorta involves L-type calcium channel inhibition

Testosterone has rapid nongenomic vasodilator effects which could be involved in protective cardiovascular actions. Several authors suggested specific mechanisms to explain this effect, but this matter was not clarified yet. We studied the actions of testosterone and cholesterol on endothelium-denuded rat aorta and their effects on the L-type Ca²⁺ current (I_Ca,L) and potassium current (I_K). Testosterone (1–100 μM) totally relaxed, in a rapid and concentration-dependent way, the aortic rings contracted by KCl or by (−)-Bay K8644 (BAY). Cholesterol also fully relaxed the contractions induced by KCl. None of the potassium channel antagonists tested (glibenclamide, tetraethylammonium and 4-aminopyridine) modified significantly the relaxant effect of testosterone. The antagonist of classic testosterone receptors, flutamide, did not modify the vasorelaxant effect of testosterone. Furthermore, testosterone and cholesterol inhibited either basal and BAY-stimulated I_Ca,L in A7r5 cells and they have no effects on I_K. In summary, our results demonstrate that cholesterol and testosterone relax rat aorta by inhibiting LTCC. This effect of testosterone is not mediated by the classic hormone receptor or by potassium channel activation. These results suggest that the vasodilator mechanism of cholesterol and testosterone is the same.

Do androgens play a beneficial role in the regulation of vascular tone? Nongenomic vascular effects of testosterone metabolites

The marked sexual dimorphism that exists in human cardiovascular diseases has led to the dogmatic concept that testosterone (Tes) has deleterious effects and exacerbates the development of cardiovascular disease in males. While some animal studies suggest that Tes does exert deleterious effects by enhancing vascular tone through acute or chronic mechanisms, accumulating evidence suggests that Tes and other androgens exert beneficial effects by inducing rapid vasorelaxation of vascular smooth muscle through nongenomic mechanisms. While this effect frequently has been observed in large arteries at micromolar concentrations, more recent studies have reported vasorelaxation of smaller resistance arteries at nanomolar (physiological) concentrations. The key mechanism underlying Tes-induced vasorelaxation appears to be the modulation of vascular smooth muscle ion channel function, particularly the inactivation of L-type voltage-operated Ca(2+) channels and/or the activation of voltage-operated and Ca(2+)-activated K(+) channels. Studies employing Tes analogs and metabolites reveal that androgen-induced vasodilation is a structurally specific nongenomic effect that is fundamentally different than the genomic effects on reproductive targets. For example, 5alpha-dihydrotestosterone exhibits potent genomic-androgenic effects but only moderate vasorelaxing activity, whereas its isomer 5beta-dihydrotestosterone is devoid of androgenic effects but is a highly efficacious vasodilator. These findings suggest that the dihydro-metabolites of Tes or other androgen analogs devoid of androgenic or estrogenic effects could have useful therapeutic roles in hypertension, erectile dysfunction, prostatic ischemia, or other vascular dysfunctions.

Androgens induce nongenomic stimulation of colonic contractile activity through induction of calcium sensitization and phosphorylation of LC20 and CPI-17

We show that androgens, testosterone and 5alpha-dihydrotestosterone (DHT), acutely (approximately 40 min) provoke the mechanical potentiation of spontaneous and agonist-induced contractile activity in mouse colonic longitudinal smooth muscle. The results using flutamide, finasteride, cycloheximide, and actinomycin D indicate that androgen-induced potentiation is dependent on androgen receptors, requires reduction of testosterone to DHT, and occurs independently of transcriptional and translational events. Using permeabilized colonic smooth muscle preparations, we could demonstrate that mechanical potentiation is entirely due to calcium sensitization of contractile machinery. In addition, DHT (10 nm) increased phosphorylation of both 20-kDa myosin light chain (LC(20)) [regulatory myosin light chain, (MLC)] and CPI-17 (an endogenous inhibitor of MLC phosphatase). Paralleling these findings, inhibition of Rho-associated Rho kinase (ROK) and/or protein kinase C (PKC) with, respectively, Y27632 and chelerythrine, prevented LC(20) phosphorylation and abolished calcium sensitization. In addition, inhibition of ROK prevents CPI-17 phosphorylation, indicating that ROK is located upstream PKC-mediated CPI-17 modulation in the signalling cascade. Additionally, androgens induce a rapid activation of RhoA and its translocation to the plasma membrane to activate ROK. The results demonstrate that androgens induce sensitization of colonic smooth muscle to calcium through activation of ROK, which in turn, activates PKC to induce CPI-17 phosphorylation. Activation of this pathway induces a potent steady stimulation of LC(20) by inhibiting MLC phosphatase and displacing the equilibrium of the regulatory subunit towards its phosphorylated state. This is the first demonstration that colonic smooth muscle is a physiological target for androgen hormones, and that androgens modulate force generation of smooth muscle contractile machinery through nongenomic calcium sensitization pathways.

Castration modifies aortic vasoreactivity and serum fatty acids in a sucrose-fed rat model of metabolic syndrome

Levels of testosterone and estradiol influence the incidence of cardiovascular diseases: generally, estrogens in females are protective before menopause; coronaropathies, hypertension, and dyslipidemias in normal men are more frequent at comparable ages. We investigated the modulation by castration of in vitro vasoreactivity, serum lipid content, and systolic blood pressure (SBP) in rats with sucrose-induced metabolic syndrome. The main characteristics of the rat model are: hypertriglyceridemia, moderately high blood pressure, intra-abdominal accumulation of adipose tissue, hyperinsulinemia, nephropathy, increased oxidative stress, and altered vasoreactivity. Male weanling rats received 30% sucrose solution for 16 weeks (metabolic syndrome; MS), controls (C) had plain water; both had commercial rodent chow. They were subdivided into five groups with two subgroups each: Group 1, intact C and MS rats, Groups 2-5, C and MS rats castrated for periods of 16, 12, 8, and 4 weeks. At the end of the study period, systolic blood pressure was measured, and blood and aortas were obtained for fatty acid determination and vasoreactivity assays, respectively. After 16 weeks' sucrose treatment MS aortas showed hypercontractility and decreased vasodilation. Palmitic and palmitoleic acids were increased in MS versus C. Arachidonic acid levels in MS were lower than in intact or castrated C. Long-term castration of 16 weeks normalized the levels of palmitic and oleic acids. With the shorter periods of castration, contractility increased and relaxation decreased in C and MS, but it was more significant in C. Regarding fatty acid composition, long-term castration increased polyunsaturated (arachidonic and eicosapentaenoic) fatty acids. The shorter periods did not modify the fatty acid profile in either C or MS. Metabolic syndrome altered SBP, aortic reactivity, and levels of fatty acids; castration of long duration normalized them in some cases.

Modulatory role of endogenous androgens on airway smooth muscle tone in isolated guinea-pig and bovine trachea; involvement of beta2-adrenoceptors, the polyamine system and external calcium

Androgens relax several smooth muscles, including the airways. They also contract ileum and myocardium via nongenomic mechanisms. To find out whether androgens modulate airway smooth muscles in different species and further assess their mechanism of action, regarding the role of beta-adrenoceptors, polyamines and extracellular Ca(2+), and the modulation of contraction, 5 alpha-dihydrotestosterone, testosterone and 5 beta-dihydrotestosterone were used. A preliminary study was performed to evaluate the effect of 5 alpha-dihydrotestosterone, a non-aromatisable derivate of testosterone, in isolated guinea-pig trachea and a more exhaustive characterisation was followed in bovine trachea, to also characterise the effect of testosterone and 5 beta-dihydrotestosterone. The androgens elicited a nongenomic epithelium-independent relaxation of the trachea which had been precontracted. In the bovine trachea, the order of potency was: testosterone>5 alpha-dihydrotestosterone=5 beta-dihydrotestosterone. This effect was inversely proportional to the magnitude of carbachol-raised tone and was independent of beta(2)-adrenoceptors, since the beta-blockers, propranolol and ICI-118,551, and beta(2)-adrenoceptor desensitisation did not modify 5 alpha-dihydrotestosterone-elicited relaxation. 5 alpha-Dihydrotestosterone was unable to displace the radiolabel, [(3)H]dihydroalprenolol, from these receptors in the binding assay. Polyamine synthesis was not involved in this androgen effect, since an ornithine decarboxylase inhibitor, alpha-difluoromethylornithine, was ineffective. The androgens were more effective relaxing bovine trachea precontracted by KCl (80 mM), suggesting a calcium entry blockade, as reported for several smooth muscles. This mechanism might be involved in the observed 5 alpha-dihydrotestosterone facilitation of salbutamol-relaxation. Androgens facilitated carbachol-elicited contraction independently of polyamine synthesis, contrary to what has been reported in the ileum. Therefore, androgens modulate tracheal smooth muscle tone which might be of importance in the regulation of airway reactivity.

Rapid actions of androgens

The biological activity of androgens is thought to occur predominantly through binding to intracellular androgen-receptors, a member of the nuclear receptor family, that interact with specific nucleotide sequences to alter gene expression. This genomic-androgen effect typically takes at least more than half an hour. In contrast, the rapid or non-genomic actions of androgens are manifested within in seconds to few minutes. This rapid effect of androgens are manifold, ranging from activation of G-protein coupled membrane androgen-receptors or sex hormone-binding globulin receptors, stimulation of different protein kinases, to direct modulation of voltage- and ligand gated ion-channels and transporters. The physiological relevance of these non-genomic androgen actions has not yet been determined in detail. However, it may contribute to modulate several second messenger systems or transcription factors, which suggests a cross-talk between the fast non-genomic and the slow genomic pathway of androgens. This review will focus on the rapid effects of androgens on cell surface and cytoplasmic level.

Relaxation of androgens on rat thoracic aorta: testosterone concentration dependent agonist/antagonist L-type Ca2+ channel activity, and 5beta-dihydrotestosterone restricted to L-type Ca2+ channel blockade

Androgen vasorelaxing action is a subject of recent interest. We investigated the involvement of l-type voltage-operated Ca(2+) channels (L-VOCCs), K(+) channels, intracellular Ca(2+) concentration ([Ca(2+)]i), and cAMP in the vasorelaxing effect of testosterone and 5beta-dihydrotestosterone (5beta-DHT) on rat thoracic aorta. Isolated aortic rings were used to study the vasorelaxing potency of testosterone and 5beta-DHT on KCl- and noradrenaline-induced contractions. Patch-clamp was used to analyze androgen effects on Ca(2+) inward and K(+) outward currents. The fluorescence technique was used to evaluate [Ca(2+)]i in single myocytes; moreover, simultaneous measurements of [Ca(2+)]i and vascular contraction were evaluated. 5beta-DHT was more potent than testosterone to relax KCl-induced contraction, but they were equipotent to relax noradrenaline contraction. l-type Ca(2+) currents were blocked by nifedipine, both androgens, and an estrogen in a concentration-dependent manner, and the order of potency was: testosterone > nifedipine > 5beta-DHT > 17beta-estradiol. We observed that testosterone has different mechanism of action by the concentration range used: at nm concentrations it was a powerful L-VOCCs antagonist, whereas at mum concentrations it was observed that: 1) its Ca(2+) antagonist property is reverted by increasing the l-type inward Ca(2+) currents (Ca(2+) agonist property); and 2) the [Ca(2+)]i and cAMP production was increased. The total K(+) currents were unaffected by testosterone or 5beta-DHT. The data show that 5beta-DHT-induced vasorelaxation is due to its selective blockade on L-VOCCs (from nm to microm concentrations), but testosterone-induced vasorelaxation involves concentration-dependent additional mechanisms: acting as an L-VOCCs antagonist at low concentrations, and increasing [Ca(2+)]i and cAMP production at high concentrations.

Evidence for the participation of calcium in non-genomic relaxations induced by androgenic steroids in rat vas deferens

BACKGROUND AND PURPOSE

Androgens cause non-genomic relaxation in several smooth muscle preparations. However, such an effect has not been investigated in rat vas deferens yet. Our purpose was to study the effect of testosterone and derivatives in this tissue.

EXPERIMENTAL APPROACH

The influence of androgens was tested on contraction and translocation of intracellular Ca(2+) induced by KCl in rat vas deferens in vitro.

KEY RESULTS

The testosterone derivative 5alpha-dihydrotestosterone produced a rapid and reversible concentration-dependent relaxation of KCl-induced contractions. Other androgens were also effective, showing the following rank order of potency: androsterone >5beta-dihydrotestosterone >androstenedione >5alpha-dihydrotestosterone >testosterone. Calcium-induced contractions were also inhibited (about 45%) by 5alpha-dihydrotestosterone (30 microM). Moreover 5alpha-dihydrotestosterone blocked the increase of intracellular Ca(2+) induced by KCl, measured by the fluorescent dye fura-2. Relaxation to 5alpha-dihydrotestosterone was resistant to the K(+) channel antagonists glibenclamide, 4-aminopyridine and charybdotoxin. It was not affected by removal of epithelium or by L-NNA (300 microM), an inhibitor of nitric oxide biosynthesis, nor by selective inhibitors of soluble guanylate cyclase, ODQ or LY 83583, indicating that nitrergic or cGMP mediated mechanisms were not involved. The androgen-induced relaxation was also not blocked by the protein synthesis inhibitor cycloheximide (300 microM) or by the classical androgen receptor flutamide (up to 100 microM), corroborating that the effect is non-genomic.

CONCLUSIONS AND IMPLICATIONS

Testosterone derivatives caused relaxation of the rat vas deferens, that did not involve epithelial tissue, K(+) channels, or nitric oxide-dependent mechanisms, but was related to a partial blockade of Ca(2+) influx.

The modulatory role of androgens and progestins in the induction of vasorelaxation in human umbilical artery

Sex steroids have been described as protectors of the cardiovascular system and one of their relevant actions is inhibition of vascular tone. However, this information has been derived from animal models. The aim of this study was to investigate the vasorelaxant properties of several progestins and androgens on the vascular tone of human umbilical artery (HUA) to elucidate their potential regulatory role on fetoplacental blood flow. HUA rings, obtained from umbilical cords at vaginal deliveries and cesarean section from term uncomplicated pregnancies, were isometrically recorded and precontracted with either KCl or serotonin. Subsequently, dehydroepiandrosterone, testosterone, progesterone and some of their 5-reduced metabolites were added at different noncumulative concentrations on KCl-induced precontraction. There were significant differences in the vasorelaxing responses to these steroids; excluding 5alpha-pregnandione, the remaining steroids induced concentration-dependent vasorelaxations. In general, androgens were more potent than progestins, with 5beta-dihydrotestosterone being the most potent one. These vasorelaxations remained unaffected by inhibitors of transcription and translation, selective steroid receptor antagonists, a nitric oxide synthase inhibitor or specific blockers of K(+) channels. Interestingly, the serotonin contraction was significantly less sensitive to steroid-induced vasorelaxation. Moreover, the contraction evoked by Ca(2+) in depolarized tissues (by KCl-Ca(2+) free solution) was prevented by steroids. These data, taken together, suggest that sex steroids (particularly androgens) induce an acute (nongenomically-mediated) vasorelaxing effect on the HUA which may be mediated by: (i) a nitric oxide-independent pathway; and/or (ii) a decrease in external Ca(2+) influx by inactivating Ca(2+) channels, but not by activating K(+) channels.

Potential role of female sex hormones in the pathophysiology of migraine

Clinical evidence indicates that female sex steroids may contribute to the high prevalence of migraine in women, as well as changes in the frequency or severity of migraine attacks that are in tandem with various reproductive milestones in women's life. While female sex steroids do not seem to be involved in the pathogenesis of migraine per se, they may modulate several mediators and/or receptor systems via both genomic and non-genomic mechanisms; these actions may be perpetuated at the central nervous system, as well as at the peripheral (neuro)vascular level. For example, female sex steroids have been shown to enhance: (i) neuronal excitability by elevating Ca(2+) and decreasing Mg(2+) concentrations, an action that may occur with other mechanisms triggering migraine; (ii) the synthesis and release of nitric oxide (NO) and neuropeptides, such as calcitonin gene-related peptide CGRP, a mechanism that reinforces vasodilatation and activates trigeminal sensory afferents with a subsequent stimulation of pain centres; and (iii) the function of receptors mediating vasodilatation, while the responses of receptors inducing vasoconstriction are attenuated. The serotonergic, adrenergic and gamma-aminobutyric acid (GABA)-ergic systems are also modulated by sex steroids, albeit to a varying degree and with potentially contrasting effects on migraine outcome. Taken together, female sex steroids seem to be involved in an array of components implicated in migraine pathogenesis. Future studies will further delineate the extent and the clinical relevance of each of these mechanisms, and will thus expand the knowledge on the femininity of migraine.

Non-genomic effect of testosterone on airway smooth muscle

BACKGROUND AND PURPOSE

Recent studies on blood vessels have provided evidence that testosterone may exert direct effects on smooth muscle. However, an acute effect on airway reactivity has not been shown yet. The aim of this study was to assess the direct effect of testosterone on the responsiveness of male adult rabbit airway smooth muscle (ASM), precontracted with 10 microM acetylcholine, 10microM carbachol or 80 mM KCl.

EXPERIMENTAL APPROACH

Contractility studies of rabbit tracheal smooth muscle were performed.

KEY RESULTS

Testosterone at concentrations of or above 1 nM had a significant relaxant effect on ASM precontracted with acetylcholine or carbachol, but did not affect ASM precontracted with KCl. The mechanical removal of airway epithelium as well as the inhibition of NO synthetase (by 100microM L-NAME) reduced the relaxation caused by testosterone. The effect of testosterone was not altered by impairing prostanoid synthesis (by 10microM indomethacin). The nitric oxide donor, sodium nitroprusside, had the same relaxant effect on ASM precontracted with either carbachol or KCl. Inhibitors of androgen receptors (10microM flutamide) or DNA transcription (100microM actinomycin D) did not alter the effect of testosterone. Prolonged incubation of ASM with 100 nM or 100 microM testosterone for 24 or 48 h did not alter their responsiveness to acetylcholine. BSA-testosterone (1pM to 100nM) relaxed significantly ASM precontracted with carbachol. The mechanical removal of airway epithelium abolished the relaxant effect of BSA-testosterone.

CONCLUSIONS AND IMPLICATIONS

Testosterone relaxes precontracted ASM via an epithelium and NO-mediated way. This effect is mediated via a non-genomic pathway.

Effect of testosterone on ex vivo vascular reactivity in man

Testosterone is reported to have an acute vasodilating action in vitro, an effect that may impart a favourable haemodynamic response in patients with chronic heart failure. However, the effect of chronic testosterone exposure on general vascular reactivity is poorly described. In the present study, fresh subcutaneous resistance arteries were obtained from patients with heart failure (n=10), healthy controls (n=9) and men with androgen-deficiency (n=17). All arteries were studied using a wire myograph to examine the effect of cumulative additions of testosterone (1 nmol/l–100 μmol/l) compared with vehicle control following maximal pre-constriction with KCl (1–100 μmol/l). The vascular reactivity of arteries from androgen-deficient patients was examined further by recording tension concentration curves to cumulative additions of noradrenaline (1 nmol/l–100 μmol/l) and U46619 (1–300 nmol/l), followed by relaxation concentration curves to additions of ACh (acetylcholine; 10 nmol/l–30 μmol/l) and SNP (sodium nitroprusside; 10 nmol–30 μmol/l) respectively. In all cases, statistical analysis was performed by ANOVA. Patients with proven androgen-deficiency were treated according to clinical recommendations for a minimum of 3 months and further arteries (n=19) were taken for experimentation using the same protocol. In all groups, testosterone was confirmed to be an acute concentration-dependent vasodilator at concentrations ≥1 μmol/l (P=0.0001). The dilating effect of testosterone was augmented in patients with androgen-deficiency prior to treatment, and this effect was abrogated following appropriate testosterone replacement. Testosterone therapy significantly reduced the normal vascular dilating response to ACh and SNP (P<0.01) and significantly increased the contractile response to noradrenaline (P<0.01), but not U46619. Testosterone is an acute dose-dependent vasodilator of resistance arteries. Physiological testosterone replacement attenuates general vascular reactivity in androgen-deficient subjects. The numerous perceived benefits of testosterone replacement may be offset by a decline in vascular reactivity and, therefore, further studies and careful monitoring of patients is recommended.

Testosterone and atherosclerosis in aging men: purported association and clinical implications

Two of the strongest independent risk factors for coronary heart disease (CHD) are increasing age and male sex. Despite a wide variance in CHD mortality between countries, men are consistently twice as likely to die from CHD than their female counterparts. This sex difference has been attributed to a protective effect of female sex hormones, and a deleterious effect of male sex hormones, upon the cardiovascular system. However, little evidence suggests that testosterone exerts cardiovascular harm. In fact, serum levels of testosterone decline with age, and low testosterone is positively associated with other cardiovascular risk factors. Furthermore, testosterone exhibits a number of potential cardioprotective actions. For example, testosterone treatment is reported to reduce serum levels of the pro-inflammatory cytokines interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha, and to increase levels of the anti-inflammatory cytokine IL-10; to reduce vascular cell adhesion molecule (VCAM)-1 expression in aortic endothelial cells; to promote vascular smooth muscle and endothelial cell proliferation; to induce vasodilatation and to improve vascular reactivity, to reduce serum levels of the pro-thrombotic factors plasminogen activator inhibitor (PAI)-1 and fibrinogen; to reduce low-density lipoprotein-cholesterol (LDL-C); to improve insulin sensitivity; and to reduce body mass index and visceral fat mass. These actions of testosterone may confer cardiovascular benefit since testosterone therapy reduces atheroma formation in cholesterol-fed animal models, and reduces myocardial ischemia in men with CHD. Consequently, an alternative hypothesis is that an age-related decline in testosterone contributes to the atherosclerotic process. This is supported by recent findings, which suggest that as many as one in four men with CHD have serum levels of testosterone within the clinically hypogonadal range. Consequently, restoration of serum levels of testosterone via testosterone replacement therapy could offer cardiovascular, as well as other, clinical advantages to these individuals.

Calcium channel blocking activity of calycosin, a major active component of Astragali Radix, on rat aorta

AIM

To investigate the vasoactivity of calycosin, a major active component of Astragali Radix.

METHODS

Experiments were performed on isolated rat thoracic aortic rings pre-contracted with phenylephrine (PHE) or KCl.

RESULTS

Calycosin produced a concentration-dependent relaxation on the tissue pre-contracted using PHE with 4.46+/-0.13 of pD(2) and 95.85%+/-2.67% of E(max); or using KCl with 4.27+/-0.05 of pD2 and 99.06%+/-2.15% of Emax, and displaced downwards the concentration-response curves of aortic rings to PHE or KCl. The relaxant effect of calycosin on denuded endothelium aortic rings was the same as on intact endothelium aortic rings, and its vasorelaxant effect was not influenced by L-NAME or indomethacin. In Ca(2+)-free solution, calycosin (30 micromol/L) did not have an effect on PHE (1 micromol/L)-induced aortic ring contraction. The effects of calycosin and nifedipine where somewhat different; calycosin decreased aortic ring contractions induced by the two agonists, but nifedipine displayed a more potent inhibitory effect on KCl-induced contractions than on PHE-induced contractions, and the vascular relaxing effects of calycosin and nifidipine were additive on PHE-induced contraction but not KCl-induced.

CONCLUSION

Calycosin is a vasorelaxant. Its action is endothelium-independent and is unrelated to intracellular Ca(2+) release. It is a noncompetitive Ca(2+) channel blocker. The effect of calycosin on Ca(2+) channel blockade may be different from that of dihydropyridines. This study demonstrated a novel pharmacological activity of calycosin, and supplied a theoretic foundation for Astragali Radix application.

Selective inhibition of L-type Ca2+ channels in A7r5 cells by physiological levels of testosterone

Testosterone has marked beneficial cardiovascular effects, many of which have been attributed to a vasodilatory action. However, the molecular target of testosterone underlying this effect is subject to debate. In this study, we have used microfluorimetry as a noninvasive means of examining whether testosterone could exert dilatory effects via inhibition of voltage-gated Ca2+ entry in the model vascular smooth muscle cell line, A7r5. Rises of [Ca2+]i evoked by 50 mm K+ -containing solution were suppressed in a concentration-dependent manner by testosterone (IC50, 3.1 nm) and by the nonaromatizable analog, 5beta-dihydrotestosterone (IC50, 6.9 nm). The effects of testosterone were apparent in the presence of pimozide (to block T-type Ca2+ channels) but not nifedipine (to block L-type Ca2+ channels). Testosterone did not alter Ca2+ mobilization from intracellular stores by the prostaglandin analog U46619 or capacitative Ca2+ entry in cells pretreated with thapsigargin. Our results indicate that testosterone, at physiological concentrations, can selectively suppress Ca2+ entry into A7r5 cells via L-type Ca2+ channels. We suggest this effect is a likely mechanism underlying its vasodilatory actions and beneficial cardiovascular effects.

Androgens Induce Relaxation of Contractile Activity in Pregnant Human Myometrium at Term: A Nongenomic Action on L-Type Calcium Channels1

It has long been accepted that progesterone regulates uterine contractile activity. However, little is known about the role of androgens in female physiology, and their importance and biological function on myometrial contractility so far have received limited attention. In this work, we examined the direct effect of androgens on the contractile activity of the isolated human myometrium. Myometrial biopsies were obtained, with consent, from pregnant women undergoing elective cesarean section at term. Each androgen tested (dehydroepiandrosterone, testosterone, 5alpha- and 5beta-dihydrotestosterone, androsterone, or androstanediol) caused a concentration-dependent inhibition of spontaneous contractile activity; a relaxing effect of these androgens was also observed on the contractions induced by high potassium (KCl) solution. Interestingly, nonpregnant myometrium was also sensitive to androgen-induced relaxation. 5beta-Dihydrotestosterone (5beta-DHT) was dramatically more potent than the other androgens in inducing myometrial relaxation in all preparations. Relaxation response to androgens had very rapid time courses and was affected by neither the specific antiandrogen (flutamide) nor inhibitors of protein synthesis (cycloheximide) and transcription (actinomycin D), implying that androgens act through a nongenomic mechanism. Importantly, 5beta-DHT significantly reduced the increase in intracellular calcium concentration associated with exposure to KCl in human myometrial smooth-muscle cells loaded with Fura-2-AM. The blockade of l-type calcium channels seems to be involved in the nongenomic relaxing action of androgens. These observations demonstrate that androgens may play a crucial role in maintaining pregnancy.

Evidence that 17alpha-estradiol is biologically active in the uterine tissue: antiuterotonic and antiuterotrophic action

BACKGROUND

17alpha-Estradiol has been considered as the hormonally inactive isomer of 17beta-estradiol. Recently, nongenomic (smooth muscle relaxation) and genomic (light estrogenic activity) effects of 17alpha-estradiol have been reported, but no reports have yet determined its possible antiestrogenic activity. Therefore, this study investigated: the nongenomic action of 17alpha-estradiol on uterine contractile activity and its potential agonist-antagonist activity on uterine growth.

METHODS

Uterine rings from rats were isometrically recorded. Different concentrations (0.2-200 microM) of 17alpha-estradiol were tested on spontaneous contraction and equimolarly compared with 17beta-estradiol. To examine the mechanism of 17alpha-estradiol action, its effect was studied in presence of beta2-antagonist (propranolol), antiestrogens (tamoxifen and ICI 182,780) or inhibitors of protein synthesis (cycloheximide) and transcription (actinomycin D). Moreover, contractions induced by high potassium (KCl) solution or calcium in depolarized tissues by KCl-calcium free solution were exposed to 17alpha-estradiol. Collaterally, we performed an uterotrophic assay in adult ovariectomized rats measuring the uterine wet weight. The administration for three days of 0.3 microM/day/Kg 17beta-estradiol was equimolarly compared with the response produced by 17alpha-estradiol. Antiuterotrophic activity was assayed by administration of 0.3 microM/day/Kg 17beta-estradiol and various doses ratios (1:1, 1:3, 1:5, and 1:100) of 17alpha-estradiol.

RESULTS

The estradiol isomers elicited an immediate relaxation, concentration-dependent and reversible on spontaneous contraction. 17alpha-Estradiol presented lower potency than 17beta-estradiol although it did not antagonize 17beta-estradiol-induced relaxation. Relaxation to 17alpha-estradiol was not inhibited by propranolol, tamoxifen, ICI 182,780, cycloheximide or actinomycin D. The KCl contractions were also sensitive to 17alpha-estradiol-induced relaxation and calcium contractions in depolarized tissues were markedly prevented by 17alpha-estradiol, implying a reduction of extracellular calcium influx through voltage-operated calcium channels (VOCCs). Uterotrophic assay detected significant increase in uterine weight using 17alpha-estradiol, which was significantly minor as compared with 17beta-estradiol. 17alpha-Estradiol, at all doses ratios, significantly antagonized the hypertrophic response of 17beta-estradiol.

CONCLUSION

17alpha-Estradiol induces a relaxing effect, which may be independent of the classical estrogen receptor, nongenomic action, apparently mediated by inactivation of VOCCs. 17alpha-Estradiol is also a weak estrogen agonist (uterotrophic response); likewise, 17alpha-estradiol may act as an antiestrogen (antiuterotrophic response). The overall data document a nongenomic relaxing action and a novel antiestrogenic action of 17alpha-estradiol, which are relevant in estrogen-mediated uterine physiology.

Interactions of androgens, green tea catechins and the antiandrogen flutamide with the external glucose-binding site of the human erythrocyte glucose transporter GLUT1

This study investigates the effects of androgens, the antiandrogen flutamide and green tea catechins on glucose transport inhibition in human erythrocytes. These effects may relate to the antidiabetogenic effects of green tea. Testosterone, 4-androstene-3,17-dione, dehydroepiandrosterone (DHEA) and DHEA-3-acetate inhibit glucose exit from human erythrocytes with half-maximal inhibitions (Ki) of 39.2+/-8.9, 29.6+/-3.7, 48.1+/-10.2 and 4.8+/-0.98 microM, respectively. The antiandrogen flutamide competitively relieves these inhibitions and of phloretin. Dehydrotestosterone has no effect on glucose transport, indicating the differences between androgen interaction with GLUT1 and human androgen receptor (hAR). Green tea catechins also inhibit glucose exit from erythrocytes. Epicatechin 3-gallate (ECG) has a Ki ECG of 0.14+/-0.01 microM, and epigallocatechin 3-gallate (EGCG) has a Ki EGCG of 0.97+/-0.13 microM. Flutamide reverses these effects. Androgen-screening tests show that the green tea catechins do not act genomically. The high affinities of ECG and EGCG for GLUT1 indicate that this might be their physiological site of action. There are sequence homologies between GLUT1 and the ligand-binding domain (LBD) of hAR containing the amino-acid triads Arg 126, Thr 30 and Asn 288, and Arg 126, Thr 30 and Asn 29, with similar 3D topology to the polar groups binding 3-keto and 17-beta OH steroid groups in hAR LBD. These triads are appropriately sited for competitive inhibition of glucose import at the external opening of the hydrophilic pore traversing GLUT1.

Vasodilating effect of norethisterone and its 5 alpha metabolites: a novel nongenomic action

Estrogens are generally administered in hormone replacement therapy in combination with synthetic progestins. Studies of cardiovascular risk factors in postmenopausal women have shown a variety of responses according to the molecular structure of the progestin used in hormone replacement therapy schemes. The present study sets out to determine the vasoactive effects of norethisterone and its 5alpha-dihydro (5alpha-norethisterone) and -tetrahydro (3alpha,5alpha-norethisterone and 3beta,5alpha-norethisterone) metabolites in isolated precontracted rat thoracic aorta. The addition of norethisterone and 3alpha,5alpha-norethisterone in rat aorta exhibited a potent, concentration-response inhibition of noradrenaline-induced contraction, while 5alpha- and 3beta,5alpha-norethisterone had very little, if any, vasorelaxing effect. Relaxation to norethisterone and 3alpha,5alpha-norethisterone had very rapid time-courses and it was neither affected by the absence of endothelium nor by the inhibitor of nitric oxide synthase, Nomega-nitro-L-arginine methyl ester (L-NAME). The addition of specific anti-androgen, anti-progestin and anti-estrogen compounds and protein synthesis inhibitors did not preclude the vasorelaxing effect of norethisterone and its 3alpha,5alpha-reduced metabolite. The results strongly suggest that these effects are not mediated by nuclear sex steroid hormone receptors. The overall data document a novel nongenomic endothelium-independent vasorelaxing action of a 19-nor synthetic progestin and one of its A-ring-reduced derivatives.

Nongenomic steroid action: controversies, questions, and answers

Steroids may exert their action in living cells by several ways: 1). the well-known genomic pathway, involving hormone binding to cytosolic (classic) receptors and subsequent modulation of gene expression followed by protein synthesis. 2). Alternatively, pathways are operating that do not act on the genome, therefore indicating nongenomic action. Although it is comparatively easy to confirm the nongenomic nature of a particular phenomenon observed, e.g., by using inhibitors of transcription or translation, considerable controversy exists about the identity of receptors that mediate these responses. Many different approaches have been employed to answer this question, including pharmacology, knock-out animals, and numerous biochemical studies. Evidence is presented for and against both the participation of classic receptors, or proteins closely related to them, as well as for the involvement of yet poorly understood, novel membrane steroid receptors. In addition, clinical implications for a wide array of nongenomic steroid actions are outlined.

Androgens and cardiovascular disease

Globally, cardiovascular disease will continue causing most human deaths for the foreseeable future. The consistent gender gap in life span of approximately 5.6 yr in all advanced economies must derive from gender differences in age-specific cardiovascular death rates, which rise steeply in parallel for both genders but 5-10 yr earlier in men. The lack of inflection point at modal age of menopause, contrasting with unequivocally estrogen-dependent biological markers like breast cancer or bone density, makes estrogen protection of premenopausal women an unlikely explanation. Limited human data suggest that testosterone exposure does not shorten life span in either gender, and oral estrogen treatment increases risk of cardiovascular death in men as it does in women. Alternatively, androgen exposure in early life (perinatal androgen imprinting) may predispose males to earlier onset of atherosclerosis. Following the recent reevaluation of the estrogen-protection orthodoxy, empirical research has flourished into the role of androgens in the progression of cardiovascular disease, highlighting the need to better understand androgen receptor (AR) coregulators, nongenomic androgen effects, tissue-specific metabolic activation of androgens, and androgen sensitivity. Novel therapeutic targets may arise from understanding how androgens enhance early plaque formation and cause vasodilatation via nongenomic androgen effects on vascular smooth muscle, and how tissue-specific variations in androgen effects are modulated by AR coregulators as well as metabolic activation of testosterone to amplify (via 5alpha-reductase to form dihydrotestosterone acting on AR) or diversify (via aromatization to estradiol acting upon estrogen receptor alpha/beta) the biological effects of testosterone on the vasculature. Observational studies show that blood testosterone concentrations are consistently lower among men with cardiovascular disease, suggesting a possible preventive role for testosterone therapy, which requires critical evaluation by further prospective studies. Short-term interventional studies show that testosterone produces a modest but consistent improvement in cardiac ischemia over placebo, comparable to the effects of existing antianginal drugs. By contrast, testosterone therapy has no beneficial effects in peripheral arterial disease but has not been evaluated in cerebrovascular disease. Erectile dysfunction is most frequently caused by pelvic arterial insufficiency due to atherosclerosis, and its sentinel relationship to generalized atherosclerosis is insufficiently appreciated. The commonality of risk factor patterns and mechanisms (including endothelial dysfunction) suggests that the efficacy of antiatherogenic therapy is an important challenge with the potential to enhance men's motivation for prevention and treatment of cardiovascular diseases.

The vasodepressor effect of androgens in pithed rats: potential role of calcium channels

Estrogens induce vasodilatation and/or hypotension in several experimental models, probably by a blockade of calcium currents. However, very little is known about the potential cardiovascular effects of androgens. We have previously shown that 5 beta-reduced androgens are more potent vasorelaxants than their precursors (delta 4-3 keto), 5-reduced progestins and 17beta-estradiol. The present study set out to investigate if this vasorelaxant effect of 5-reduced androgens is operative in vivo in the analysis of the potential vasodepressor effect of these compounds in vagosympathectomized, pithed rats. After increasing diastolic blood pressure (DBP) by a continuous infusion of norepinephrine (0.059 micromol x kg(-1)min(-1)), i.v. bolus injections of 3 alpha-hydroxy-5 beta-androstan-17-one (etiocholanolone), 5 beta-dihydrotestosterone (5 beta-DHT), and its isomer 5 alpha-dihydrotestosterone (5 alpha-DHT) (5-25 micromol x kg(-1) each) produced, separately, dose-dependent vasodepressor responses. These responses were biphasic: an immediate fall in DBP (reaching the nadir within 1.7 min) was followed by a further slow decrease that reached a maximum between 80 and 100 min after steroid administration. The order of potency of androgens in decreasing DBP was: 5 beta-DHT>5 alpha-DHT=etiocholanolone for the short-lasting response and 5 alpha-DHT>5 beta-DHT>or=etiocholanolone for the longer lasting response. Importantly, the same doses of these compounds produced no significant changes in heart rate. Moreover, 5 beta-DHT significantly antagonized the vasopressor responses to methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluromethylphenyl)-pyridine-5-carboxylate (Bay K 8644) with a blocking profile similar to that of nifedipine (NIF). This finding suggests that a blockade of voltage-operated calcium channels may be involved in androgen-induced hypotension.

Rapid action of cortisol and testosterone on lipogenic enzymes in a fresh water fish Oreochromis mossambicus: short-term in vivo and in vitro study

Rapid action of steroid hormones on lipid metabolism is not reported so far in any vertebrate. The present study was intended to evaluate the quick actions of cortisol and testosterone on enzymes, namely malic enzyme (ME), glucose-6-phosphate dehydrogenase (G6PDH), and isocitrate dehydrogenase (ICDH) in Oreochromis mossambicus. Cortisol and testosterone produced rapid and opposite effects on the lipogenic enzymes studied. Cortisol significantly decreased the activities of ME, G6PDH, as early as 5 min and ICDH as early as 10 min in vitro (10(-6) M), and 30 min in vivo (0.1 microg/g body wt.) whereas the same doses of testosterone significantly stimulated the activity of all enzymes as early as 5 min in vitro and 30 min in vivo. Actinomycin D treatment did not interfere with the inhibiting effect of cortisol on enzyme activities when measured at 10 min in the in vitro system. The transcriptional inhibitor appeared to partially block the effect of cortisol in vivo. The stimulatory effect of testosterone was insensitive to the action of actinomycin D both in vivo and in vitro. These effects appear to be brought about independently of new protein synthesis because the rapid responses occurred within a latent period of 5-30 min and were insensitive to the action of actinomycin D, suggesting a non-genomic action.

Differential effects of progesterone and 17beta-estradiol on the Ca(2+) entry induced by thapsigargin and endothelin-1 in in situ endothelial cells

The effects of progesterone and 17beta-estradiol on Ca(2+) signaling in in situ endothelial cells were investigated using front-surface fluorometry of fura-2-loaded strips of porcine aortic valve. Progesterone inhibited the thapsigargin-induced sustained [Ca(2+)](i) elevation (IC(50)=33.9 microM, n=4), while 17beta-estradiol added a transient [Ca(2+)](i) elevation. Progesterone and 17beta-estradiol had no significant effect on the thapsigargin-induced [Ca(2+)](i) elevations in the absence of extracellular Ca(2+). A Mn(2+)-induced decline of fluorescent intensity at 360 nm excitation was accelerated by thapsigargin. This acceleration was completely reversed by progesterone, but not by 17beta-estradiol. Progesterone inhibited, and 17beta-estradiol enhanced the endothelin-1 (ET-1)-induced [Ca(2+)](i) elevation, while both had no effect on the ET-1-induced Ca(2+) release observed in the absence of extracellular Ca(2+) or in the pertussis toxin-treated strips. Progesterone and 17beta-estradiol thus had different effects on Ca(2+) signaling, especially on Ca(2+) influx, in endothelial cells.