Red cell sodium in DOCA-salt hypertension: a Brattleboro study.

The alteration of red cell Na+ content (Na+i), its causes and the possible relationship to the development of DOCA-salt hypertension were studied in Brattleboro rats. A pronounced hypertension developed in heterozygous (non-DI) animals that synthesize vasopressin (VP) although no substantial Na+i elevation was observed in their erythrocytes. In contrast, Na+i rose progressively in red cells of homozygous VP-deficient (DI) rats in which only marginal increase of systolic blood pressure was found after six weeks of DOCA-salt regimen. DOCA-salt treatment of non-DI rats did not cause major alterations in ouabain-resistant (OR) net Na+ uptake or ouabain-sensitive (OS) net Na+ extrusion but moderately increased furosemide-sensitive (FS) Rb+ uptake. The same treatment of DI rats doubled Na+i by an increased OR net Na+ uptake (due to a major elevation in both Na(+)-K+ cotransport and Na+ leak). Consequently, OS net Na+ extrusion was augmented in red cells of these animals. This was accompanied by an about threefold elevated FS Rb+ uptake. It can be concluded that a) the alterations of OR and/or OS Na+ or K+ transport observed in erythrocytes of Brattleboro DI rats are not essential for the development of severe DOCA-salt hypertension, b) red cell ion transport abnormalities revealed in DOCA-salt treated DI rats might be rather ascribed to cell potassium depletion, and c) increased inward Na(+)-K+ cotransport and Na+ leak causes red cell Na+i elevation that stimulates Na(+)-K+ pump activity.     

Signs of attenuated depression-like behavior in vasopressin deficient Brattleboro rats

Vasopressin, a peptide hormone functioning also as a neurotransmitter, neuromodulator and regulator of the stress response is considered to be one of the factors related to the development and course of depression. In the present study, we have tested the hypothesis that congenital deficit of vasopressin in Brattleboro rats leads to attenuated depression-like behavior in tests modeling different symptoms of depression. In addition, hypothalamic-pituitary-adrenocortical axis activity was investigated. Vasopressin deficient rats showed signs of attenuated depression-like behavior in forced swimming and sucrose preference tests, while their behavior on elevated plus maze was unchanged. Vasopressin deficiency had no influence on basal levels of ACTH and corticosterone and had only mild impact on hormonal activation in response to forced swimming and plus-maze exposure. However, vasopressin deficient animals showed higher level of dexamethasone induced suppression of corticosterone response to restraint stress and higher basal levels of corticotropin-releasing hormone mRNA in the hypothalamic paraventricular nucleus. In conclusion, present data obtained in vasopressin deficient rats show that vasopressin is involved in the development of depression-like behavior, in particular of the coping style and anhedonia. Moreover, behavioral and endocrine responses were found to be dissociated. We suggest that brain vasopressinergic circuits distinct from those regulating the HPA axis are involved in generating depression-like behavior.     

Mild DOCA-salt hypertension: sympathetic system and role of renal nerves

This study examines the effects of VEGF-121 therapy in an animal model of preeclampsia induced by overexpression of soluble VEGF receptor 1 (sVEGFR-1). At day 8 of gestation, CD-1 mice were implanted with subcutaneous osmotic pumps containing either VEGF-121 or vehicle and fitted with telemetric blood pressure (BP) catheters for continuous BP monitoring (days 8-18 of gestation). On day 9, the animals in the VEGF-121 group were randomly allocated for injection with adenovirus carrying sVEGFR-1 or the murine immunoglobulin G2α Fc fragment (mFc) as virus control (Adv-sVEGFR-1; Adv-mFc). Animals in the vehicle group were injected with Adv-sVEGFR-1. On day 18, mice were euthanized, placentas and pups weighted, carotid arteries isolated, and their responses studied in vitro using a wire myograph for isometric tension recording. In mice overexpressing sVEGFR-1, treatment with VEGF-121 significantly reduced BP from days 10 to 18 of gestation compared with that of vehicle. VEGF-sVEGFR-1 animals had significantly higher vasorelaxant response to sodium nitroprusside and significantly lower contractile response to the thromboxane agonist (U-46619) compared with that of the vehicle-sVEGFR-1 mice. Phenylephrine and acetylcholine responses did not significantly vary between the VEGF-sVEGFR-1 and the vehicle-sVEGFR-1 mice. Average pup weight was significantly lower in the vehicle-sVEGFR-1 group compared with the VEGF-sVEGFR-1 and VEGF-mFc groups. In conclusion, VEGF-121 therapy attenuates vascular dysfunction and diminishes intrauterine growth abnormality in an animal model of preeclampsia induced by overexpression of sVEGFR-1. Modulation of VEGF pathway turns into a promising therapeutic approach of preeclampsia.     

Effect of chemical sympathectomy on the development of DOCA-salt hypertension in rats

Structurally based resistance and vascular reactivity of the posterior body to noradrenaline were studied in normotensive rats and rats with DOCA-salt hypertension. The hypertension was induced in rats with intact sympathetic nervous system and in rats subjected to neonatal sympathectomy with guanethidine. During the prehypertensive stage, vascular sensitivity of the smooth muscles to noradrenaline was enhanced, with structural lesions being observed only in steady hypertension. Elevation of arterial pressure was accompanied by an increased vascular response to the stimulation of the sympathetic nerves. Sympathectomy prevented arterial pressure elevation and structural alterations in the vessels.     

DOCA-salt hypertension in cats

The possibility of reproducing DOCA-salt hypertension in cats has been explored. It has been shown that administration of DOCA and sodium chloride may result in the development of a hypertensive condition in some of cats. Unilateral nephrectomy increases the probability of hypertension occurrence. To attain a steady and noticeable (up to 190 +/- 8/146 +/- 7 mm Hg) elevation of arterial pressure, it is necessary that appreciable amounts of DOCA and sodium chloride be administered for a long time (during 6 months) in the presence of unilateral nephrectomy. The hypertension thus induced is marked by the increased (71%) overall peripheral resistance and by the decreased cardiac output, which rises for a short period in the course of hypertension development.     

Effects of water-deprivation on aldosterone production in Brattleboro male rats congenitally lacking vasopressin

Effects of water-deprivation on several metabolic parameters and on plasma aldosterone concentration have been investigated in male Brattleboro rats homozygous for hypothalamic diabetes insipidus (DI) and in male Long-Evans rats (LE) as controls. Two separate experiments were performed over a period of 72 hours: 1) to determine the global effect of water-deprivation, water deprived rats were compared with hydrated animals, 2) to elucidate the specific effect of dehydration alone, water-deprived rats were compared with similar food-restricted, but water-supplied DI and LE rats. In hydrated animals, plasma aldosterone concentration was close to 50% less in DI rats than in LE rats. After 72 hours, plasma aldosterone values increased mainly because of dehydration and this increase was greater in DI rats than in LE rats. At the same time, plasma aldosterone concentration remained lower in DI rats compared to LE rats. The changes in plasma aldosterone concentration after dehydration and possible reasons for the impairment of aldosterone production in DI rats are discussed.     

Age-dependent salt hypertension in Dahl rats: fifty years of research

Fifty years ago, Lewis K. Dahl has presented a new model of salt hypertension - salt-sensitive and salt-resistant Dahl rats. Twenty years later, John P. Rapp has published the first and so far the only comprehensive review on this rat model covering numerous aspects of pathophysiology and genetics of salt hypertension. When we summarized 25 years of our own research on Dahl/Rapp rats, we have realized the need to outline principal abnormalities of this model, to show their interactions at different levels of the organism and to highlight the ontogenetic aspects of salt hypertension development. Our attention was focused on some cellular aspects (cell membrane function, ion transport, cell calcium handling), intra- and extrarenal factors affecting renal function and/or renal injury, local and systemic effects of renin-angiotensin-aldosterone system, endothelial and smooth muscle changes responsible for abnormal vascular contraction or relaxation, altered balance between various vasoconstrictor and vasodilator systems in blood pressure maintenance as well as on the central nervous and peripheral mechanisms involved in the regulation of circulatory homeostasis. We also searched for the age-dependent impact of environmental and pharmacological interventions, which modify the development of high blood pressure and/or organ damage, if they influence the salt-sensitive organism in particular critical periods of development (developmental windows). Thus, severe self-sustaining salt hypertension in young Dahl rats is characterized by pronounced dysbalance between augmented sympathetic hyperactivity and relative nitric oxide deficiency, attenuated baroreflex as well as by a major increase of residual blood pressure indicating profound remodeling of resistance vessels. Salt hypertension development in young but not in adult Dahl rats can be attenuated by preventive increase of potassium or calcium intake. On the contrary, moderate salt hypertension in adult Dahl rats is attenuated by superoxide scavenging or endothelin-A receptor blockade which do not affect salt hypertension development in young animals.     

Increased release of atrial natriuretic polypeptides in rats with DOCA-salt hypertension

This study compared atrial and plasma concentrations of immunoreactive alpha-rat atrial natriuretic polypeptide (i alpha-rANP) in rats given tap water (control), a 1% saline solution (salt), deoxycorticosterone acetate (DOCA) and DOCA plus 1% saline solution (DOCA-salt) after 1 and 8 weeks of treatment. DOCA (100 mg/kg) was given by implanting a piece of silicon rubber impregnated with DOCA subcutaneously. Atrial i alpha-rANP increased, while plasma i alpha-rANP decreased with time in all groups. Atrial concentration of i alpha-rANP was significantly lower in the DOCA-salt group than in the other groups at 1 week, and was reduced in the DOCA and DOCA-salt groups as compared to the control group at 8 weeks. On the other hand, plasma concentration of i alpha-rANP was significantly higher in the DOCA and the DOCA-salt groups than in the control group at 1 week; the DOCA and DOCA-salt group values were also higher than the control and salt group values at 8 weeks. Atrial concentration of i alpha-rANP was inversely correlated with systolic blood pressure in the all rats at 1 week (r = 0.48, p less than 0.001) and at 8 weeks (r = 0.33, p less than 0.05). Plasma concentration of i alpha-rANP was positively correlated with systolic blood pressure at 8 weeks (r = 0.37, p less than 0.05). In addition, there was a significant positive correlation between plasma/atrial ratio of i alpha-rANP concentration and systolic blood pressure at either stage (r = 0.41, p less than 0.01 at 1 week; r = 0.40, p less than 0.01 at 8 weeks). Thus, it seems likely that the release of ANPs is increased in response to expansion of extracellular fluid volume or elevation of blood pressure, modifying the development of hypertension in DOCA-salt rats.     

Desmopressin, but not vasopressin, decreases activity of the hypothalamo-neurohypophysial system in Brattleboro rats

The pituitary neural lobe of homozygous Brattleboro rats has high rates of glucose utilization not affected by chronic treatment with exogenous vasopressin, despite attenuation of polydipsia and polyuria. We evaluated whether this effect may result from the inability of vasopressin to affect the hypothalamo-neurohypophysial metabolism or from the development of resistance to chronic vasopressin treatment. We used the [14C]deoxyglucose method to compare 28-h effects of vasopressin treatment (5 U/kg, i.m., twice a day) with that of desmopressin (100 micrograms/kg, i.p., once a day), a long-lasting antidiuretic hormone, on glucose utilization of the hypothalamo-neurohypophysial system and related structures in conscious homozygous Brattleboro rats. Vasopressin and desmopressin reduced water intake, plasma osmolality and plasma Na+ concentration similarly. Vasopressin decreased glucose utilization in the supraoptic nucleus, subfornical organ and median preoptic nucleus, but did not alter activity in the paraventricular nucleus and neural lobe. Desmopressin decreased glucose utilization in all these structures. The results indicate that desmopressin has a more potent inhibitory action on the hypothalamo-neurohypophysial system than vasopressin over this short duration of treatment. The lack of response in the neural lobe from chronic treatment with vasopressin seems to be due to its inability to affect the paraventricular nucleus metabolism. The maintenance of metabolic activity in the paraventricular nucleus of vasopressin-treated Brattleboro rats suggests that this structure contributes importantly to the metabolism of neural lobe.     

Disorders of cell acquisition in the brain of rats deficient in vasopressin (Brattleboro mutant)

Neural cell acquisition and certain features of its underlying mechanisms were determined in the forebrain, cerebellum and olfactory bulbs of Brattleboro rats which were either heterozygous (control) or homozygous for a hereditary deficiency in vasopressin synthesis. In comparison with heterozygotes, the amount of DNA, which provides a measure of total cell number, was decreased in homozygous animals. The magnitude of the effect varied markedly from one brain part to another. Although more [³H]thymidine was retained in homozygous animals, the corrected values for DNA labeling showed a reduction in comparison with heterozygous rats. This decrease in mitotic activity preceded the reduction in brain cell number. The observed disturbances in brain cell acquisition of the Brattleboro mutant indicate a possible role for vasopressin in early brain development.     

Polyphenols restore endothelial function in DOCA-salt hypertension: role of endothelin-1 and NADPH oxidase

Red wine polyphenols (RWPs) have been reported to exert beneficial effects in preventing cardiovascular diseases, such as hypertension. We studied the effects of chronic treatment with RWPs and apocynin, an inhibitor of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, on blood pressure, endothelial function, and oxidative status in deoxycorticosterone acetate (DOCA)-salt-induced hypertension. Rats were administered RWPs (40 mg/kg) or apocynin (33 microg/kg) daily by gavage for 5 weeks. Plasma catechin levels were detected only after RWP treatment. RWPs and apocynin prevented both the increase in systolic blood pressure and the proteinuria induced by DOCA-salt. Plasma malonyldialdehyde levels, urinary iso-prostaglandin F(2alpha) excretion, aortic superoxide production, and aortic NADPH oxidase activity were found to be increased in animals of the DOCA group. RWP and apocynin treatments reduced these parameters in DOCA-salt rats, having no effect on control rats. However, only RWPs reduced the increase in plasma endothelin-1 (ET-1) levels and aortic p22(phox) gene overexpression found in DOCA-salt animals. RWPs and apocynin also improved the blunted endothelium-dependent relaxation response to acetylcholine in noradrenaline-precontracted aortic rings. All these results suggest that chronic treatment with RWPs prevents hypertension and vascular dysfunction. RWPs prevent vascular oxidative stress by inhibiting NADPH oxidase activity and/or by reducing ET-1 release.     

Arginine vasopressin deficient Brattleboro rats fail to develop tolerance to the hypothermic effects of ethanol

We have tested the hypothesis that animals with reduced levels of arginine vasopressin (AVP) would show reduced tolerance to ethanol. Brattleboro rats either heterozygous or homozygous for the diabetes insipidus (DI) trait and normal Sprague-Dawley rats were exposed to ethanol vapor for 21 days. Two days later, tolerance was evaluated by monitoring body temperature reductions after intraperitoneal injection of 2 g/kg (20% w/v) ethanol. Under the same conditions of chronic ethanol exposure, Sprague-Dawley rats, but not Brattleboro rats, displayed tolerance to the hypothermic effects of intraperitoneal ethanol. This phenomenon did not appear to be related to differences in ethanol metabolism or blood alcohol levels in Brattleboro rats. These data support a possible role for AVP in the development or maintenance of tolerance.     

Induction of V2 receptors in renal medulla of homozygous Brattleboro rats by arginine vasopressin

Homozygous Brattleboro rats display pronounced diabetes insipidus and when treated continuously with arginine vasopressin (AVP) acquire the ability to produce concentrated urine. In this study, the effects of continual AVP replacement on the pharmacological properties of the renal medullary V2 receptor and coupling to adenylate cyclase were examined. Osmotic minipumps that delivered AVP at four different rates were implanted into male homozygous Brattleboro rats. At the end of the 14 day treatment period, urine osmolalities were 280 +/- 24, 474 +/- 105, 1777 +/- 304 and 2202 +/- 175 mOsm/kg H2O for the 0, 31.25, 62.5 and 125 ng/hr treatment groups, respectively. Plasma AVP levels were below the level of detection for the 0 and 31.25 ng/hr treatment groups, and were 2.5 +/- 0.5 and 6.5 +/- 1.8 pg/ml for the 62.5 and 125 ng/hr treatment groups. Saturation experiments using [3H] AVP and renal medullary membranes revealed binding site concentrations of 57 +/- 9, 84 +/- 23, 164 +/- 17 and 150 +/- 18 fmol/mg protein for the 0, 31.25, 62.5 and 125 ng/hr treatment groups, respectively. AVP-stimulated cyclic AMP accumulation was enhanced in renal medullary membranes prepared from the 62.5 and 125 ng/hr treatment groups when compared to that in the 0 and 31.25 ng/hr treatment groups. From these results, it appears that circulating AVP is necessary for expression of functional V2 receptors in the homozygous Brattleboro rat renal medulla.     

Effect of chronic vasopressin treatment on alcohol drinking of Brattleboro HZ and DI rats

Preference for alcohol was determined for three groups of male and female rats, 100–150 days old, comprised of: (1) Long Evans (LE); (2) LE-derived Brattleboro heterozygous (HZ); and (3) Brattleboro homozygous (DI) animals afflicted with diabetes insipidus due to vasopressin deficiency. Each alcohol drinking test was run over 11 days during which food, water and an ethyl alcohol solution, increased in concentration from 3% to 25%, were freely available. Following an initial preference screen, 100 milli-units of vasopressin tannate in oil was administered subcutaneously, during a second preference test, once per day to each animal. This treatment ameliorated the polydipsia-polyuria syndrome characteristic of the DI sub-strain of Brattleboro rat. Administration of the peptide to both the LE or HZ animals exerted no effect on g/kg intake nor on the proportional measure of alcohol to water. However, in the DI rat of either gender, vasopressin reduced the mean absolute gram intake of alcohol over concentrations to resemble that of the other LE and/or HZ groups. These results demonstrate that vasopressin serves to normalize the intake of alcohol in the DI rat by virtue of the elimination of the diabetic condition. However, since vasopressin fails to alter alcohol consumption of the HZ and LE rats, it would appear that this neuroactive peptide may play only a minor role in the CNS mechanisms governing the voluntary selection of alcohol.     

Prevention of hypertension in DOCA-salt rats by an inhibitor of soluble expoxide hydrolase

Cyclooxygenase and lipoxygenase metabolism of arachidonic acid produces compounds important in cardiovascular diovascular control. Further, arachidonic acid can be metabolised by cytochrome p450 to produce epoxyeicosatrienoic acids (EETs). These derivatives are inactivated by soluble epoxide hydrolase (sEH). The potential role of these EETs in hypertension and cardiac remodelling has been determined using the selective sEH inhibitor, N-adamantyl-N′-dodecylurea (ADU), in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Experiments were performed on male Wistar rats following uninephrectomy alone (UNX rats) or uninephrectomy with administration of DOCA (25 mg every fourth day subcutaneously) and 1% NaCl in drinking water (DOCA-salt rats). ADU (10 mg/kg/d subcutaneously) was administered for 2wk starting 2wk after surgery. Cardiovascular structure and function were determined using organ wet weights, histological analysis of collagen and inflammation, isolated heart and thoracic aortic ring preparation, and electrophysiological measurements. DOCA-salt hypertensive rats developed hypertension, hypertrophy, perivascular and interstitial fibrosis, endothelial dysfunction, and prolongation of the cardiac action potential duration within 4 wk. Administration of ADU prevented the further increase in systolic blood pressure and left-ventricular wet weight and normalized endothelial function. ADU treatment did not change inflammatory cell infiltration, collagen deposition, or cardiac action potential duration. EETs may be involved in the development of hypertension and endothelial dysfunction in DOCA-salt rats, but not in excessive collagen deposition or electrophysiological abnormalities.     

Biomechanical response of arterial wall to DOCA-salt hypertension in growing and middle-aged rats

To study arterial remodeling in response to hypertension, Deoxycortico-sterone acetate (DOCA)-salt hypertension was induced in immature (aged 16 weeks) and middle-aged (48 weeks) rats, and biomechanical properties and wall dimensions of common carotid arteries were determined. Arterial segments were excised at 10 or 16 weeks postoperatively from the immature rats and at 16 weeks from the middle-aged ones. In vitro pressure-diameter tests were performed under normal (in Krebs-Ringer solution), active (norepinephrine), and passive (papaverine) conditions. Non-treated, age-matched rats (26, 32, and 64 weeks) were used to obtain control data. Wall thickness at in vivo blood pressure level was increased by hypertension at all ages; however, there were no significant changes in inner diameter. In hypertensive rats, arterial outer diameter was smaller under normal condition than under passive condition, indicating the increase of smooth muscle tone by hypertension. Diameter reduction developed by norepinephrine was increased by hypertension, which was significant above 100 mmHg; however, there were no significant differences between hypertensive and normotensive arteries, if compared at respective in vivo blood pressures. No significant differences were observed in wall stiffness at in vivo pressure. Wall hoop stress at in vivo blood pressure had a significant positive correlation with the pressure in 26-week old arteries. However, there were no differences in the stress between hypertension and normotension in 32- and 64-week old arteries. These results were essentially similar to previous ones observed in Goldblatt hypertension and in younger animals. Age-related differences in arterial wall remodeling were not clearly observed.     

Prevention of hypertension in DOCA-salt rats by an inhibitor of soluble epoxide hydrolase

Cyclooxygenase and lipoxygenase metabolism of arachidonic acid produces compounds important in cardiovascular control. Further, arachidonic acid can be metabolised by cytochrome p450 to produce epoxyeicosatrienoic acids (EETs). These derivatives are inactivated by soluble epoxide hydrolase (sEH). The potential role of these EETs in hypertension and cardiac remodelling has been determined using the selective sEH inhibitor, N-adamantyl-N'-dodecylurea (ADU), in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Experiments were performed on male Wistar rats following uninephrectomy alone (UNX rats) or uninephrectomy with administration of DOCA (25 mg every fourth day subcutaneously) and 1% NaCl in drinking water (DOCA-salt rats). ADU (10 mg/kg/d subcutaneously) was administered for 2 wk starting 2 wk after surgery. Cardiovascular structure and function were determined using organ wet weights, histological analysis of collagen and inflammation, isolated heart and thoracic aortic ring preparations, and electrophysiological measurements. DOCA-salt hypertensive rats developed hypertension, hypertrophy, perivascular and interstitial fibrosis, endothelial dysfunction, and prolongation of the cardiac action potential duration within 4 wk. Administration of ADU prevented the further increase in systolic blood pressure and left-ventricular wet weight and normalized endothelial function. ADU treatment did not change inflammatory cell infiltration, collagen deposition, or cardiac action potential duration. EETs may be involved in the development of hypertension and endothelial dysfunction in DOCA-salt rats, but not in excessive collagen deposition or electrophysiological abnormalities.