Central effects of mineralocorticoid antagonist RU-28318 on blood pressure of DOCA-salt hypertensive rats

Decreased 11β-Hydroxysteroid Dehydrogenase Type 2 Expression in the Kidney May Contribute to Nicotine/Smoking-Induced Blood Pressure Elevation in Mice

[Figure: see text].

Rodent models of heart failure: an updated review

Heart failure (HF) is one of the major health and economic burdens worldwide, and its prevalence is continuously increasing. The study of HF requires reliable animal models to study the chronic changes and pharmacologic interventions in myocardial structure and function and to follow its progression toward HF. Indeed, during the past 40 years, basic and translational scientists have used small animal models to understand the pathophysiology of HF and find more efficient ways of preventing and managing patients suffering from congestive HF (CHF). Each species and each animal model has advantages and disadvantages, and the choice of one model over another should take them into account for a good experimental design. The aim of this review is to describe and highlight the advantages and drawbacks of some commonly used HF rodents models, including both non-genetically and genetically engineered models, with a specific subchapter concerning diastolic HF models.

Tumor necrosis factor-α: regulation of renal function and blood pressure

Tumor necrosis factor-α (TNF-α) is a pleiotropic cytokine that becomes elevated in chronic inflammatory states such as hypertension and diabetes and has been found to mediate both increases and decreases in blood pressure. High levels of TNF-α decrease blood pressure, whereas moderate increases in TNF-α have been associated with increased NaCl retention and hypertension. The explanation for these disparate effects is not clear but could simply be due to different concentrations of TNF-α within the kidney, the physiological status of the subject, or the type of stimulus initiating the inflammatory response. TNF-α alters renal hemodynamics and nephron transport, affecting both activity and expression of transporters. It also mediates organ damage by stimulating immune cell infiltration and cell death. Here we will summarize the available findings and attempt to provide plausible explanations for such discrepancies.

Protective effect of estrogens on the brain of rats with essential and endocrine hypertension

Estrogen neuroprotection has been shown in pathological conditions damaging the hippocampus, such as trauma, aging, neurodegeneration, excitotoxicity, oxidative stress, hypoglycemia, amyloid-β peptide exposure and ischemia. Hypertensive encephalopathy also targets the hippocampus; therefore, hypertension seems an appropriate circumstance to evaluate steroid neuroprotection. Two experimental models of hypertension, spontaneously hypertensive rats (SHR) and deoxycorticosterone (DOCA)-salt hypertensive rats, develop hippocampal abnormalities, which include decreased neurogenesis in the dentate gyrus, astrogliosis, low expression of brain-derived neurotrophic factor (BDNF) and decreased number of neurons in the hilar region, with respect of their normotensive strains Wistar Kyoto (WKY) and Sprague-Dawley rats. After estradiol was given for 2 weeks to SHR and DOCA-treated rats, both hypertensive models normalized their faulty hippocampal parameters. Thus, estradiol treatment positively modulated neurogenesis in the dentate gyrus of the hippocampus, according to bromodeoxyuridine incorporation and doublecortin immunocytochemistry, decreased reactive astrogliosis, increased BDNF mRNA and protein expression in the dentate gyrus and increased neuronal number in the hilar region of the dentate gyrus. A role of local estrogen biosynthesis is suggested in SHR, because basal aromatase mRNA in the hippocampus and immunoreactive aromatase protein in cell processes of the dentate gyrus were highly expressed in these rats. Estradiol further stimulated aromatase-related parameters in SHR but not in WKY. These observations strongly support that a combination of exogenous estrogens to those locally synthesized might better alleviate hypertensive encephalopathy. These studies broaden estrogen neuroprotective functions to the hippocampus of hypertensive rat models.

Involvement of brain-derived neurotrophic factor and neurogenesis in oestradiol neuroprotection of the hippocampus of hypertensive rats

The hippocampus of spontaneously hypertensive rats (SHR) and deoxycorticosterone (DOCA)-salt hypertensive rats shows decreased cell proliferation and astrogliosis as well as a reduced number of hilar cells. These defects are corrected after administration of 17β-oestradiol (E(2) ) for 2 weeks. The present work investigated whether E(2) treatment of SHR and of hypertensive DOCA-salt male rats modulated the expression of brain-derived neurotrophic factor (BDNF), a neurotrophin involved in hippocampal neurogenesis. The neurogenic response to E(2) was simultaneously determined by counting the number of doublecortin-immunopositive immature neurones in the subgranular zone of the dentate gyrus. Both hypertensive models showed decreased expression of BDNF mRNA in the granular zone of the dentate gyrus, without changes in CA1 or CA3 pyramidal cell layers, decreased BDNF protein levels in whole hippocampal tissue, low density of doublecortin (DCX)-positive immature neurones in the subgranule zone and decreased length of DCX+ neurites in the dentate gyrus. After s.c. implantation of a single E(2) pellet for 2 weeks, BDNF mRNA in the dentate gyrus, BDNF protein in whole hippocampus, DCX immunopositive cells and the length of DCX+ neurites were significantly raised in both SHR and DOCA-salt-treated rats. These results indicate that: (i) low BDNF expression and deficient neurogenesis distinguished the hippocampus of SHR and DOCA-salt hypertensive rats and (ii) E(2) was able to normalise these biologically important functions in the hippocampus of hypertensive animals.

Aldosterone in the brain

Pharmacological and physiological phenomena suggest that cells somewhere inside the central nervous system are responsive to aldosterone. Here, we present the fundamental physiological limitations for aldosterone action in the brain, including its limited blood-brain barrier penetration and its substantial competition from glucocorticoids. Recently, a small group of neurons with unusual sensitivity to circulating aldosterone were identified in the nucleus of the solitary tract. We review the discovery and characterization of these neurons, which express the enzyme 11beta-hydroxysteroid dehydrogenase type 2, and consider alternative proposals regarding sites and mechanisms for mineralocorticoid action within the brain.

Protective effects of estradiol in the brain of rats with genetic or mineralocorticoid-induced hypertension

Abnormalities of hippocampus and hypothalamus are commonly observed in rats with genetic (SHR) or mineralocorticoid/salt-induced hypertension. In the hippocampus, changes include decreased cell proliferation in the dentate gyrus (DG), astrogliosis and decreased neuronal density in the hilus, whereas in the hypothalamus expression of arginine vasopressin (AVP) is markedly elevated. Here, we report that estradiol treatment overturns these abnormalities. We used 16-week-old male SHR with blood pressure (BP) approximately 190 mmHg and their normotensive Wistar-Kyoto (WKY) controls, and male Sprague-Dawley rats made hypertensive by administration of 10mg deoxycorticosterone acetate (DOCA) every other day plus 1% NaCl as drinking fluid for 4 weeks (BP approximately 160 mmHg). Controls received oil vehicle plus 1% NaCl only. Half of the animals in each group were implanted s.c. with a single estradiol benzoate pellet weighing 14 mg for 2 weeks. Estradiol-treated SHR and DOCA-salt rats showed, in comparison to their respective steroid-free groups: (a) enhanced proliferation in the DG measured by bromodeoxyuridine incorporation; (b) decreased number of glial fibrillary acidic protein (GFAP) immunopositive astrocytes; (c) increased density of neurons in the hilus of the DG, and (d) decreased hypothalamic AVP mRNA expression. These results indicate that neuronal and glial alterations of hypertensive models are plastic events reversible by steroid treatment. The estradiol protective effects may be of pharmacological interest to attenuate the consequences of hypertensive encephalopathy.

Abnormalities of the hippocampus are similar in deoxycorticosterone acetate-salt hypertensive rats and spontaneously hypertensive rats

Hippocampal neuropathology is a recognised feature of the brain in spontaneously hypertensive rats (SHR), but similar studies are lacking in another model of hypertension, the mineralocorticoid-salt-treated rat. The present study aimed to compare changes in hippocampal parameters in 16-week-old male SHR (blood pressure approximately 190 mmHg) and their normotensive Wistar-Kyoto controls, with those of male Sprague-Dawley rats receiving (i) 10 mg deoxycorticosterone acetate (DOCA) every other day during 3 weeks and drinking 1% NaCl solution (blood pressure approximately 160 mmHg) and normotensive controls treated with (ii) DOCA and drinking water, (iii) drinking water only or (iv) 1% NaCl only. In these experimental groups, we determined: (i) cell proliferation in the dentate gyrus (DG) using the 5-bromo-2'-deoxyuridine-labelling technique; (ii) the number of glial fibrillary acidic protein (GFAP) positive astrocytes under the CA1, CA3 and DG; (iii) the number of apolipoprotein E (ApoE) positive astrocytes as a marker of potential neuronal damage; and (iv) the number of neurones in the hilus of the DG, taken as representative of neuronal density in other hippocampal subfields. Changes were remarkably similar in both models, indicating a decreased cell proliferation in DG, an increased number of astrocytes immunopositive for GFAP and ApoE and a reduced number of hilar neurones. Although hypertension may be a leading factor for these abnormalities, endocrine mechanisms may be involved, because hypothalamic-pituitary function, mineralocorticoid receptors and sensitivity to mineralocorticoid treatment are stimulated in SHR, whereas high exogenous mineralocorticoid levels circulate in DOCA-treated rats. Thus, in addition to the deleterious effects of hypertension, endocrine factors may contribute to the abnormalities of hippocampus in SHR and DOCA-treated rats.

Prenatal glucocorticoid exposure alters hypothalamic-pituitary-adrenal function and blood pressure in mature male guinea pigs

Pregnant guinea pigs were treated with dexamethasone (1 mg kg(-1)) or vehicle on days 40-41, 50-51 and 60-61 of gestation, after which animals delivered normally. Adult male offspring were catheterized at 145 days of age and subjected to tests of hypothalamic-pituitary-adrenal (HPA) axis function in basal and activated states. Animals exposed to dexamethasone in utero (mat-dex) exhibited increased hippocampus-to-brain weight ratio, increased adrenal-to-body weight ratio and increased mean arterial pressure. There were no effects on gestation length, birth weight and postnatal growth. There were no overall differences in diurnal plasma adrenocorticotropic hormone (ACTH) and cortisol profiles, though there were subtle differences during the subjective afternoon between control and mat-dex offspring. A significant decrease in initial ACTH suppression was observed following dexamethasone injection in mat-dex offspring compared to control offspring. Molecular analysis revealed significantly increased MR mRNA expression in the limbic system and particularly in the dentate gyrus in mat-dex offspring. In the anterior pituitary, both pro-opiomelanocortin (POMC) and glucocorticoid receptor (GR) mRNA levels were significantly elevated in mat-dex offspring. In conclusion, (1) repeated prenatal treatment with synthetic glucocorticoid (sGC) permanently programmes organ growth, blood pressure and HPA regulation in mature male offspring and these changes involve modification of corticosteroid receptor expression in the brain and pituitary; (2) the effects of prenatal sGC exposure on HPA function appear to change as a function of age, indicating the importance of investigating HPA and cardiovascular outcome at multiple time points throughout life.

Role of central mineralocorticoid receptors in cardiovascular disease

Mineralocorticoids act directly through their receptors in specific centers in the central nervous system, kidneys, heart, and vascular smooth muscle to mediate hemodynamic homeostasis. These steroids also modulate renal and cardiovascular function indirectly through the autonomic nervous system. Complex homeostatic mechanisms under normal hormonal control become pathogenic when there is an excess of regulatory hormone. Experiments in which mineralocorticoid receptor antagonists or antisense oligodeoxynucleotides were administered centrally have clearly shown that centrally mediated effects on salt appetite, baroreceptor function, and autonomic drive to the renal and cardiovascular systems are crucial to the pathogenesis of hypertension and cardiovascular disease of hyperaldosteronism, and certain forms of genetic hypertension.