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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Role of renal nerves in development of hypertension in DOCA-salt model in rats: a telemetric approach

Centrally mediated hyperactivity of the autonomic nervous system contributes to DOCA hypertension; however, the targeted peripheral vascular bed(s) remain unclear. We propose that if renal sympathetic activity is a factor in the development of DOCA-salt hypertension, then renal denervation (RDNX) should attenuate the hypertensive response. In protocol 1, uninephrectomized RDNX (n = 9) and sham-denervated (n = 6) Sprague-Dawley rats were allowed free access to 0.9% NaCl solution and 0.1% NaCl diet. Mean arterial pressure (MAP) and heart rate were telemetrically recorded for 4 days before and 36 days after DOCA (100 mg/rat) implantation; sodium and water balances were recorded daily. Protocol 2 was similar except that saline intake in sham rats (n = 7) was matched to that observed in RDNX rats of protocol 1 for 30 days; for the last 10 days, the rats were allowed free access to saline. Before DOCA in protocol 1, MAP was lower (P < 0.05) in RDNX rats (99 +/- 1 mmHg) compared with sham rats (111 +/- 3 mmHg); however, heart rate and sodium and water balances were similar between groups. RDNX attenuated the MAP response to DOCA by approximately 50% (DeltaMAP = 22 +/- 3 mmHg, where Delta is change in MAP) when compared with sham rats (DeltaMAP = 38 +/- 6). RDNX rats consumed significantly less saline than sham rats, and cumulative sodium and water balances were reduced by 33% and 23%, respectively. In protocol 2, a similar pattern in MAP elevation was observed in RDNX and saline-restricted, sham-denervated rats even when saline restriction was removed. These results indicate that the renal sympathetic nerves are important in hypertension development but that other factors are also involved.     

Co-expression of vasopressin with beta-endorphin and dynorphin in individual cells from the ovaries of Brattleboro and Long-Evans rats: immunocytochemical studies

The distribution of arginine-vasopressin (AVP)-, oxytocin-, beta-endorphin (beta-EP)- and dynorphin-immunoreactive cells was examined by peroxidase-antiperoxidase (PAP) immunocytochemistry in the ovaries of Brattleboro and Long-Evans (LE) rats. The ovarian distribution of the peptide-immunoreactivity is indistinguishable between the two strains. AVP- and beta-EP-immunoreactivity is co-localized in the majority of luteal cells, and in some cells scattered in the interstitial tissue. Of the AVP/beta-EP-positive cells, 1-2% also contained immunoreactive (ir)-dynorphin. Some cells in the interstitium contained only ir-AVP (approximately 50%) or only ir-dynorphin (approximately 5%); in the corpora lutea, however, no luteal cells appeared to contain only one peptide. AVP-immunoreactivity is also present in theca cells surrounding secondary and large, antral follicles; ir-oxytocin was not observed in any ovarian cell type in the rat. These data suggest that most luteal, and some interstitial, cells in the ovary have the capacity to produce and store up to three different neuropeptides.     

Impact of altered protein structures on the intracellular traffic of a mutated vasopressin precursor from Brattleboro rats

The rat vasopressin precursor, synthesized in the reticulocyte lysate system under the direction of in vitro transcribed mRNA, is processed and correctly delivered to the lumen of added microsomal vesicles. Translation of mRNA for the mutant (Brattleboro) vasopressin precursor which lacks a translational stop codon as a consequence of a frame-shift mutation, gives rise to a mutated protein (B-mutant precursor) with a C-terminal poly(lysine) sequence encoded by the poly(A) tail. Upon addition of microsomal membranes, the mutated precursor has access to the lumen of the vesicles as indicated by removal of the signal peptide; however, the C-terminal part with the poly(lysine) tail remains outside the vesicles as shown by its sensitivity to proteinase K. When a modified RNA, including a stop codon located similarly to that found in the cDNA encoding the normal precursor, is translated in the presence of microsomal membranes, the resulting product (S-mutant precursor) is refractory to proteolysis by exogenously added proteinase K. Analysis of the microsomal membranes indicates, however, that the C-terminus of the S-mutant precursor is still anchored within membranes. For studying the intracellular transport of the mutated precursor Xenopus laevis oocytes were injected with various RNA constructs. To monitor the transport steps from the endoplasmic reticulum to the Golgi compartment an RNA encoding a glycosylation site within the S-mutant precursor sequence was constructed. The resulting GS-mutant precursor is synthesized in the oocyte but not secreted into the incubation medium, completely in contrast to the normal vasopressin precursor which can be detected in the incubation bath 4 h after injection of the respective RNA. The sensitivity of the GS-mutant precursor carbohydrate side chain to endoglycosidase H treatment suggests that the mutated precursor does not reach the Golgi apparatus.