Influence of gender and estrous cycle on plasma and renal catecholamine levels in rats

Age and sex mediated effects of estrogen and Β3-adrenergic receptor on cardiovascular pathophysiology

Sex differences are consistently identified in determining the prevalence, manifestation, and response to therapies in several systemic disorders, including those affecting the cardiovascular (CV), skeletal muscle, and nervous system. Interestingly, such differences are often more noticeable as we age. For example, premenopausal women experience a lower risk of CV disease than men of the same age. While at an advanced age, with menopause, the risk of cardiovascular diseases and adverse outcomes increases exponentially in women, exceeding that of men. However, this effect appears to be reversed in diseases such as pulmonary hypertension, where women are up to seven times more likely than men to develop an idiopathic form of the disease with symptoms developing ten years earlier than their male counterparts. Explaining this is a complex question. However, several factors and mechanisms have been identified in recent decades, including a role for sex hormones, particularly estrogens and their related receptors. Furthermore, an emerging role in these sex differences has also been suggested for β-adrenergic receptors (βARs), which are essential regulators of mammalian physiology. It has in fact been shown that βARs interact with estrogen receptors (ER), providing further demonstration of their involvement in determining sexual differences. Based on these premises, this review article focused on the β3AR subtype, which shows important activities in adipose tissue but with new and interesting roles in regulating the function of cardiomyocytes and vascular cells. In detail, we examined how β3AR and ER signaling are intertwined and whether there would be sex- and age-dependent specific effects of these receptor systems.

Zonisamide attenuates pressure overload-induced myocardial hypertrophy in mice through proteasome inhibition

Myocardial hypertrophy is a pathological thickening of the myocardium which ultimately results in heart failure. We previously reported that zonisamide, an antiepileptic drug, attenuated pressure overload-caused myocardial hypertrophy and diabetic cardiomyopathy in murine models. In addition, we have found that the inhibition of proteasome activates glycogen synthesis kinase 3 (GSK-3) thus alleviates myocardial hypertrophy, which is an important anti-hypertrophic strategy. In this study, we investigated whether zonisamide prevented pressure overload-caused myocardial hypertrophy through suppressing proteasome. Pressure overload-caused myocardial hypertrophy was induced in mice by trans-aortic constriction (TAC) surgery. Two days after the surgery, the mice were administered zonisamide (10, 20, 40 mg·kg-1·d-1, i.g.) for four weeks. We showed that zonisamide administration significantly mitigated impaired cardiac function. Furthermore, zonisamide administration significantly inhibited proteasome activity as well as the expression levels of proteasome subunit beta types (PSMB) of the 20 S proteasome (PSMB1, PSMB2 and PSMB5) and proteasome-regulated particles (RPT) of the 19 S proteasome (RPT1, RPT4) in heart tissues of TAC mice. In primary neonatal rat cardiomyocytes (NRCMs), zonisamide (0.3 μM) prevented myocardial hypertrophy triggered by angiotensin II (Ang II), and significantly inhibited proteasome activity, proteasome subunits and proteasome-regulated particles. In Ang II-treated NRCMs, we found that 18α-glycyrrhetinic acid (18α-GA, 2 mg/ml), a proteasome inducer, eliminated the protective effects of zonisamide against myocardial hypertrophy and proteasome. Moreover, zonisamide treatment activated GSK-3 through inhibiting the phosphorylated AKT (protein kinase B, PKB) and phosphorylated liver kinase B1/AMP-activated protein kinase (LKB1/AMPKα), the upstream of GSK-3. Zonisamide treatment also inhibited GSK-3's downstream signaling proteins, including extracellular signal-regulated kinase (ERK) and GATA binding protein 4 (GATA4), both being the hypertrophic factors. Collectively, this study highlights the potential of zonisamide as a new therapeutic agent for myocardial hypertrophy, as it shows potent anti-hypertrophic potential through the suppression of proteasome.

Disrupted Circadian Rhythm of Epinephrine in Males With Youth-Onset Type 2 Diabetes

Context

Blood pressure and plasma catecholamines normally decline during sleep and rapidly increase in early morning. This is blunted in adults with type 2 diabetes (T2D).

Objective

We hypothesize that increased sympatho-adrenal activity during sleep differentiates youth with T2D from nondiabetic obese youth and lean youth.

Methods

Fasting spot morning and 24-hour urines were collected in obese adolescents with and without T2D, and normal-weight controls. Fractionated free urine catecholamines (epinephrine, norepinephrine, and dopamine) were measured, and the ratio of fasting spot morning to 24-hour catecholamines was calculated.

Results

Urinary 24-hour catecholamine levels were comparable across the 3 groups. Fasting morning epinephrine and the ratio of fasting morning/24-hour epinephrine were higher in youth with T2D (P = 0.004 and P = 0.035, respectively). In males, the ratio of fasting morning/24-hour epinephrine was also higher in youth with T2D (P = 0.005). In females, fasting morning norepinephrine and the ratio of fasting morning/24-hour dopamine were lower in obese youth with and without T2D (P = 0.013 and P = 0.005, respectively) compared with lean youth. Systolic blood pressure was higher in diabetic participants than other groups; males trended higher than females.

Conclusion

Circadian rhythm in catecholamines is disrupted in youth-onset T2D, with a blunted overnight fall in urinary epinephrine in males. Conversely, fasting morning norepinephrine and dopamine levels were lower in obese females with or without T2D. Higher nocturnal catecholamines in males with T2D might associate with, or predispose to, hypertension and cardiovascular complications. Lower catecholamine excretion in females with obesity might serve an adaptive, protective role.

Sex/Gender- and Age-Related Differences in β-Adrenergic Receptor Signaling in Cardiovascular Diseases

Sex differences in cardiovascular disease (CVD) are often recognized from experimental and clinical studies examining the prevalence, manifestations, and response to therapies. Compared to age-matched men, women tend to have reduced CV risk and a better prognosis in the premenopausal period. However, with menopause, this risk increases exponentially, surpassing that of men. Although several mechanisms have been provided, including sex hormones, an emerging role in these sex differences has been suggested for β-adrenergic receptor (β-AR) signaling. Importantly, β-ARs are the most important G protein-coupled receptors (GPCRs), expressed in almost all the cell types of the CV system, and involved in physiological and pathophysiological processes. Consistent with their role, for decades, βARs have been considered the first targets for rational drug design to fight CVDs. Of note, β-ARs are seemingly associated with different CV outcomes in females compared with males. In addition, even if there is a critical inverse correlation between β-AR responsiveness and aging, it has been reported that gender is crucially involved in this age-related effect. This review will discuss how β-ARs impact the CV risk and response to anti-CVD therapies, also concerning sex and age. Further, we will explore how estrogens impact β-AR signaling in women.

The potential protective effects of estradiol and 2-methoxyestradiol in ischemia reperfusion-induced kidney injury in ovariectomized female rats

AIMS

Investigating the impact of 17β estradiol (E2) and its endogenous non-hormonal metabolite 2-methoxyestradiol (2ME) on renal ischemia-reperfusion (RIR) induced kidney injury in ovariectomized (OVX) rats and the role of catechol-O-methyltransferase (COMT) in their effects.

MAIN METHODS

Eighty female rats were allocated into eight groups. Control group, Sham group, OVX group, OVX and RIR group, OVX + RIR + E2 group, OVX + RIR + 2ME group, OVX + RIR + E2 + Entacapone group and OVX + RIR + 2ME + Entacapone group, respectively. Twenty-four hours post RIR, creatinine (Cr) and blood urea nitrogen (BUN) were determined in serum, while malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), Glutathione (GSH), myeloperoxidase (MPO), as well as the expressions of COMT, hypoxia inducible factor-1α (HIF-1α) and tyrosine hydroxylase (TH) were assessed in the kidney tissues.

KEY FINDINGS

Serum Cr, BUN, MPO, as well as HIF-1α and TH expressions were significantly higher with concomitant decrease in COMT expression, SOD and CAT activities and GSH content observed in OVX and RIR group compared to sham group. E2 and 2ME treatment significantly ameliorated all parameters measured in OVX and RIR rats. On the other hand, Entacapone significantly decreased the effect of E2, with no effect on 2ME treatment.

SIGNIFICANCE

E2 ameliorates RIR-induced kidney injury and this effect is mediated, at least in part, via its COMT-mediated conversion to 2ME. Thus, 2ME by the virtue of its pleiotropic pharmacological effects can be used as a safe and effective treatment of RIR injury.

Obesity: sex and sympathetics

Obesity increases sympathetic nerve activity (SNA) in men, but not women. Here, we review current evidence suggesting that sexually dimorphic sympathoexcitatory responses to leptin and insulin may contribute. More specifically, while insulin increases SNA similarly in lean males and females, this response is markedly amplified in obese males, but is abolished in obese females. In lean female rats, leptin increases a subset of sympathetic nerves only during the high estrogen proestrus reproductive phase; thus, in obese females, because reproductive cycling can become impaired, the sporadic nature of leptin-induced sympathoexcitaton could minimize its action, despite elevated leptin levels. In contrast, in males, obesity preserves or enhances the central sympathoexcitatory response to leptin, and current evidence favors leptin’s contribution to the well-established increases in SNA induced by obesity in men. Leptin and insulin increase SNA via receptor binding in the hypothalamic arcuate nucleus and a neuropathway that includes arcuate neuropeptide Y (NPY) and proopiomelanocortin (POMC) projections to the paraventricular nucleus. These metabolic hormones normally suppress sympathoinhibitory NPY neurons and activate sympathoexcitatory POMC neurons. However, obesity appears to alter the ongoing activity and responsiveness of arcuate NPY and POMC neurons in a sexually dimorphic way, such that SNA increases in males but not females. We propose hypotheses to explain these sex differences and suggest areas of future research.

Differential Effects of Acute Treatment With Antipsychotic Drugs on Peripheral Catecholamines

Antipsychotic drugs represent the most effective treatment for chronic psychotic disorders. The newer second generation drugs offer the advantage of fewer neurological side-effects compared to prior drugs, but many cause serious metabolic side-effects. The underlying physiology of these side-effects is not well-understood, but evidence exists to indicate that the sympathetic nervous system may play an important role. In order to examine this possibility further, we treated separate groups of adult female rats acutely with either the first generation antipsychotic drug haloperidol (0.1 or 1 mg/kg) or the second generation drugs risperidone (0.25 or 2.5 mg/kg), clozapine (2 or 20 mg/kg), olanzapine (3 or 15 mg/kg) or vehicle by intraperitoneal injection. Blood samples were collected prior to drug and then 30, 60, 120, and 180 mins after treatment. Plasma samples were assayed by HPLC-ED for levels of norepinephrine, epinephrine, and dopamine. Results confirmed that all antipsychotics increased peripheral catecholamines, although this was drug and dose dependent. For norepinephrine, haloperidol caused the smallest maximum increase (+158%], followed by risperidone (+793%), olanzapine (+952%) and clozapine (+1,684%). A similar pattern was observed for increases in epinephrine levels by haloperidol (+143%], olanzapine (+529%), risperidone (+617%) then clozapine (+806%). Dopamine levels increased moderately with olanzapine [+174%], risperidone [+271%], and clozapine [+430%]. Interestingly, levels of the catecholamines did not correlate strongly with each other prior to treatment at baseline, but were increasingly correlated after treatment as time proceeded. The results demonstrate antipsychotics can potently regulate peripheral catecholamines, in a manner consistent with their metabolic liability.

Skeletal phenotype of the neuropeptide Y knockout mouse

Neuropeptide Y (NPY) is involved in multiple processes such as behavior, energy and bone metabolism. Previous studies have relied on global NPY depletion to examine its effects on bone. However, this approach is unable to distinguish the central or local source of NPY influencing bone. Our aim was to identify which cells within the skeleton express Npy and establish a model that will enable us to differentiate effects of NPY derived from different cell types. We have generated the NPY floxed (NPY^flox) mice using CRISPR technology. By crossing the NPY^flox mice with Hypoxanthine Phosphoribosyltransferase 1 (Hprt)-cre to generate a global knockout, we were able to validate and confirm loss of Npy transcript and protein in our global NPYKO. Global deletion of NPY results in a smaller femoral cortical cross-sectional area (-12%) and reduced bone strength (-18%) in male mice. In vitro, NPY-deficient bone marrow stromal cells (BMSCs) showed increase in osteogenic differentiation detected by increases in alkaline phosphatase staining and bone sialoprotein and osteocalcin expression. Despite both sexes presenting with increased adiposity, female mice had no alterations in bone mass, suggesting that NPY may have sex-specific effects on bone. In this study we identified Npy expression in the skeleton and examined the effect of global NPY depletion to bone mass. The differential impact of NPY deletion in cortical and cancellous compartments along with differences in phenotypes between in vitro and in vivo, highlights the complex nature of NPY signaling, indicative of distinct sources that can be dissected in the future using this NPY^flox model.

Estrogen deficiency compromised the β2AR-Gs/Gi coupling: implications for arrhythmia and cardiac injury

Estrogen and β₂-adrenergic receptors (β₂AR) play important roles in the processes that protect the heart. Here, we investigated how ovariectomy influenced the β₂AR downstream pathways in the context of catecholaminergic stress. In vivo and in vitro stress models were developed in female Sprague-Dawley (SD) rats by epinephrine (Epi) treatments. The cardiac function was evaluated at in vivo and in vitro levels in terms of contraction, rhythm, and injury. We found that myocardial contractility was not significantly different between Sham and ovariectomized (OVX) group rats in the normal state. However, Epi pretreatment decreased the contractility and increased abnormal rhythms especially in OVX group, which were attributed to lack of estrogen. Inhibition of the β₂AR-Gi-PI3K/p38MAPK pathway with ICI118,551, PTX or LY294002 increased contractility and aggravated Epi-induced injury on cardiomyocytes, decreased p38MAPK phosphorylation, and only increased arrhythmia in Sham group. These results indicated that OVX exacerbated cardiac injury and abnormal rhythms through β₂AR-Gi-PI3K and β₂AR-Gi-p38MAPK pathways, respectively. In normal state, the levels of activated Gi were similar in both groups, but those of cAMP and activated Gs were higher in OVX group. Epi treatment increased activated Gi (especially in Sham group) and activated Gs and cAMP in Sham group but decreased it in OVX group. These results suggested that estrogen increased the Gi activity in normal and stress states and Gs activity in stress state. These results indicated that lack of estrogen impaired the β₂AR-Gs/Gi coupling during stress which compromised cardiac contractility and increased abnormal rhythms.

Breaking the Cycle: Estrous Variation Does Not Require Increased Sample Size in the Study of Female Rats

Despite the striking differences between male and female physiology, female physiology is understudied. In response, the National Institutes of Health is promulgating new policies to increase the use of female organisms in preclinical research. Females are commonly believed to have greater variability than males because of the estrous cycle, but recent studies call this belief into question. Effects of estrous cycling on mean arterial pressure were assessed in female Dahl S rats using telemetry and vaginal cytometry and found that estrous cycling did not affect mean arterial pressure magnitude or variance. Data from the PhysGen arm of the Program for Genomic Applications was used to compare male and female variance and coefficient of variation in 142 heart, lung, vascular, kidney, and blood phenotypes, each measured in hundreds to thousands of individual rats from over 50 inbred strains. Seventy-four of 142 phenotypes from this data set demonstrated a sex difference in variance; however, 59% of these phenotypes exhibited greater variance in male rats rather than female. Remarkably, a retrospective power analysis demonstrated that only 16 of 74 differentially variable phenotypes would be detected when using an experimental cohort large enough to detect a difference in magnitude. No overall difference in coefficient of variation between male and female rats was detected when analyzing these 142 phenotypes. We conclude that variability of 142 traits in male and female rats is similar, suggesting that differential treatment of males and females for the purposes of experimental design is unnecessary until proven otherwise, rather than the other way around.

Gender-related differences in β-adrenergic receptor-mediated cardiac remodeling

Cardiac remodeling is the pathological basis of various cardiovascular diseases. In this study, we found gender-related differences in β-adrenergic receptor (AR)-mediated pathological cardiac remodeling. Cardiac remodeling model was established by subcutaneous injection of isoprenaline (ISO) for 14 days. Heart rate (HR), mean arterial pressure (MAP), and echocardiography were obtained on 7th and 14th days during ISO administration. Myocardial cross-sectional area and the ratio of heart mass to tibia length (HM/TL) were detected to assess cardiac hypertrophy. Picro-Sirius red staining (picric acid + Sirius red F3B) was used to evaluate cardiac fibrosis. Myocardial capillary density was assessed by immunohistochemistry for von Willebrand factor. Further, real-time PCR was used to measure the expression of β1-AR and β2-AR. Results showed that ISO induced cardiac remodeling, the extent of which was different between female and male mice. The extent of increase in cardiac wall thickness, myocardial cross-sectional area, and collagen deposition in females was less than that in males. However, no gender-related difference was observed in HR, MAP, cardiac function, and myocardial capillary density. The distinctive decrease of β2-AR expression, rather than a decrease of β1-AR expression, seemed to result in gender-related differences in cardiac remodeling.

Testosterone Replacement Therapy Prevents Alterations of Coronary Vascular Reactivity Caused by Hormone Deficiency Induced by Castration

The present study aimed to determine the effects of chronic treatment with different doses of testosterone on endothelium–dependent coronary vascular reactivity in male rats. Adult male rats were divided into four experimental groups: control (SHAM), castrated (CAST), castrated and immediately treated subcutaneously with a physiological dose (0.5 mg/kg/day, PHYSIO group) or supraphysiological dose (2.5 mg/kg/day, SUPRA group) of testosterone for 15 days. Systolic blood pressure (SBP) was assessed at the end of treatment through tail plethysmography. After euthanasia, the heart was removed and coronary vascular reactivity was assessed using the Langendorff retrograde perfusion technique. A dose–response curve for bradykinin (BK) was constructed, followed by inhibition with 100 μM L-NAME, 2.8 μM indomethacin (INDO), L-NAME + INDO, or L-NAME + INDO + 0.75 μM clotrimazole (CLOT). We observed significant endothelium–dependent, BK–induced coronary vasodilation, which was abolished in the castrated group and restored in the PHYSIO and SUPRA groups. Furthermore, castration modulated the lipid and hormonal profiles and decreased body weight, and testosterone therapy restored all of these parameters. Our results revealed an increase in SBP in the SUPRA group. In addition, our data led us to conclude that physiological concentrations of testosterone may play a beneficial role in the cardiovascular system by maintaining an environment that is favourable for the activity of an endothelium–dependent vasodilator without increasing SBP.

Roles of estrogen and progesterone in modulating renal nerve function in the rat kidney

The maintenance of extracellular Na⁺ and Cl^- concentrations in mammals depends, at least in part, on renal function. It has been shown that neural and endocrine mechanisms regulate extracellular fluid volume and transport of electrolytes along nephrons. Studies of sex hormones and renal nerves suggested that sex hormones modulate renal function, although this relationship is not well understood in the kidney. To better understand the role of these hormones on the effects that renal nerves have on Na⁺ and Cl^- reabsorption, we studied the effects of renal denervation and oophorectomy in female rats. Oophorectomized (OVX) rats received 17β-estradiol benzoate (OVE, 2.0 mg·kg^-1·day^-1, sc) and progesterone (OVP, 1.7 mg·kg^-1·day^-1, sc). We assessed Na⁺ and Cl^- fractional excretion (FE_Na⁺ and FE_Cl^-, respectively) and renal and plasma catecholamine release concentrations. FE_Na⁺, FE_Cl^-, water intake, urinary flow, and renal and plasma catecholamine release levels increased in OVX vs control rats. These effects were reversed by 17β-estradiol benzoate but not by progesterone. Renal denervation did not alter FE_Na⁺, FE_Cl^-, water intake, or urinary flow values vs controls. However, the renal catecholamine release level was decreased in the OVP (236.6±36.1 ng/g) and denervated rat groups (D: 102.1±15.7; ODE: 108.7±23.2; ODP: 101.1±22.1 ng/g). Furthermore, combining OVX + D (OD: 111.9±25.4) decreased renal catecholamine release levels compared to either treatment alone. OVE normalized and OVP reduced renal catecholamine release levels, and the effects on plasma catecholamine release levels were reversed by ODE and ODP replacement in OD. These data suggest that progesterone may influence catecholamine release levels by renal innervation and that there are complex interactions among renal nerves, estrogen, and progesterone in the modulation of renal function.

Neuropeptide Y mediates the short-term hypometabolic effect of estrogen deficiency in mice

BACKGROUND

Estrogen deficiency increases body weight or total and central adiposity and decreases energy expenditure. Hypothalamic neuropeptide Y (NPY) expression is altered by estrogen deficiency in rodents, but the long-term consequences on energy homeostasis are unknown.

OBJECTIVE

To investigate the role of NPY in the changes in energy expenditure and physical activity, as well as the associated changes in body weight and composition in response to short-term and long-term estrogen deficiency.

DESIGN

Sham and ovariectomy (OVX) operations were performed at 8 weeks of age in wild-type (WT) and NPY(-/-) mice. Energy expenditure, physical activity, body composition and weight, as well as food intake were measured at 10-18 days (short-term) and 46-54 days (long-term) after OVX.

RESULTS

OVX influences energy homeostasis differently at early compared with later time-points. At the early but not the late time point, OVX in WT mice reduced oxygen consumption and energy expenditure and tended to reduce resting metabolic rate. Interestingly, these effects of short-term estrogen deficiency were ablated by NPY deletion, with NPY(-/-) mice exhibiting significant increases in energy expenditure and resting metabolic rate. In addition to these hypermetabolic effects, OVX NPY(-/-) mice exhibited significantly lower body weight and whole-body fat mass relative to OVX WT controls at the short-term but not the long-term time point. Food intake and physical activity were unaltered by OVX, but NPY(-/-) mice exhibited significant reductions in these parameters relative to WT.

CONCLUSION

The effects of estrogen deficiency to reduce energy metabolism are transient, and NPY is critical to this effect as well as the early OVX-induced obesity.