DR Rats Research Articles

Dual-tracer assessment of coupling between cardiac sympathetic neuronal function and downregulation of beta-receptors during development of hypertensive heart failure of rats.

Heart failure is associated with activation of the sympathetic nervous system and downregulation of beta-receptors. However, the coupling between cardiac sympathetic neuronal function and the beta-receptor during the development of hypertensive heart failure is not clear. We determined cardiac neuronal function and beta-receptors with a dual-tracer method of [131I]metaiodobenzylguanidine (MIBG) and 125I-cyanopindolol (ICYP) in Dahl salt-sensitive (DS) and salt-resistant (DR) rats. The rats were fed an 8% NaCl diet after the age of 6 weeks. Blood pressure was raised to >200 mm Hg at 12 weeks in DS rats and remained elevated until 18 weeks, but only slightly in DR rats. Left ventricular (LV) function of DS rats was preserved at 12 weeks but deteriorated at 18 weeks. Despite a 56% reduction of cardiac norepinephrine (NE) content at 12 weeks in DS rats, neither MIBG nor ICYP uptake in DS rats was different from that of DR rats. At 18 weeks, both MIBG and ICYP uptakes decreased, by 52% and 39%, respectively, in association with 71% reduction of cardiac NE, in DS rats. MIBG uptake of the LV was homogeneous at 6 weeks but was lower in the LV endocardial regions at 18 weeks in DS rats. The present results indicate that cardiac sympathetic neuronal function is relatively preserved at the compensated, hypertrophic stage of DS rats but deteriorates in association with beta-receptor downregulation at the failing stage. The cardiac neuronal dysfunction occurs heterogeneously. A combination of scintigraphic portrayal of beta-receptors with MIBG should provide valuable information regarding sympathetic nerve signaling in living hearts.

Difference in water intake but not in renal sympathetic nerve activity in response to central salt-loading or angiotensin II in awake Dahl salt-sensitive and -resistant rats

Experiments were conducted to examine whether renal sympathetic nerve activity (RSNA) and water intake in response to central salt-loading or angiotensin II (A II) differ between freely-moving Dahl salt-sensitive (DS) and -resistant (DR) rats maintained on a low-salt diet. Intracerebroventricular (i.c.v.) administration of hypertonic saline (0.3 M, 1 μl/min, 20 min) or A II (100 ng/1 μl) evoked water intake, pressor response and suppression of RSNA in both strains. The cumulative water intake in DS rats over a 60-min period after i.c.v. infusion of hypertonic saline or A II was significantly attenuated compared with that in DR rats. The RSNA response did not show a significant difference between the strains. These results demonstrate that water intake, but not RSNA response to acute central salt-loading or A II differ between awake DR and DS rats.

ET(A) receptor blockade prevents increased tissue endothelin-1, vascular hypertrophy, and endothelial dysfunction in salt-sensitive hypertension.

Sodium plays an important role in the pathogenesis and therapy of hypertension, a major risk factor for cardiovascular disease. This study investigated the involvement of endothelin in vascular alterations in salt-induced Dahl hypertension. Salt-sensitive (DS) and salt-resistant (DR) Dahl rats were treated with a high-sodium diet (NaCl 4%) with or without ET(A) receptor antagonist LU135252 for two months, and effects of treatments on systolic blood pressure, vascular endothelin-1 (ET-1) protein content, aortic hypertrophy, and vascular reactivity of isolated aortic rings were studied. In DS rats, a high-sodium diet increased systolic pressure (190+/-4 versus 152+/-2 mm Hg, P<.05) and aortic ET-1 protein content (4.2-fold, P<.0001) and induced aortic hypertrophy as assessed by tissue weight (P<.0001). Sodium diet markedly reduced NO-mediated endothelium-dependent relaxations to acetylcholine (49+/-4% versus 81+/-4%, P<.0001) and contractions to ET-1 (92+/-7 versus 136+/-8% of KCl, P=.0011). ET-1 tissue levels were highly and inversely correlated with endothelium-dependent relaxations (r=0.931, P<.0001) and contractions to ET (r=0.77, P=.0007). LU135252 treatment reduced systolic blood pressure only in part (168+/-3 versus 190+/-4 mm Hg, P<.05) but normalized sodium-induced changes of vascular reactivity, tissue ET-1 protein content, and vascular structure (P<.001 versus sodium). None of these effects were observed in DR rats. These results suggest that ET-1 acts as a local mediator of vascular dysfunction and aortic hypertrophy in Dahl salt-induced hypertension. ET(A) receptor antagonism may have therapeutic potential for lowering vascular ET-1 content, improving endothelial function, and preventing structural changes in salt-sensitive hypertension.

Role of natriuretic peptide receptor type C in Dahl salt-sensitive hypertensive rats.

The natriuretic peptide system is suggested to be involved in the pathogenesis of salt-sensitive hypertension; a recent report indicated that disruption of the atrial natriuretic peptide precursor gene caused salt-sensitive hypertension. However, natriuretic peptide receptor (NPR)-A knockout mice did not show enhanced salt sensitivity of blood pressure. The aim of the present study was to investigate the role of NPR-C, the other receptor for atrial natriuretic peptide, in increased salt sensitivity of blood pressure. Dahl salt-sensitive (DS) and salt-resistant (DR) rats were placed on a 0.3% or 8% NaCl diet for 4 weeks. Blood pressure was elevated by salt loading only in DS rats. RNase protection assay demonstrated that NPR-C transcript level in the kidney was reduced by chronic salt loading in both DR and DS rats, whereas expression of NPR-A and NPR-B was not altered. The reduction of NPR-C mRNA in response to salt loading was enhanced in DS compared with DR rats. In situ hybridization indicated that the salt-induced NPR-C change was attributed mainly to suppressed expression of NPR-C in the podocytes. NPR-C gene expression was regulated by salt loading in a tissue-specific manner; the marked decrease in NPR-C mRNA by salt loading was seen only in the kidney. These data suggest that the exaggerated salt-induced reduction of NPR-C in the kidney of DS rats may play an important role in the pathogenesis of salt hypertension in this animal, possibly related to impaired renal sodium excretion.

Dietary restriction maintains the basal rate of somatotrope renewal in later life in male rats

We investigated the impact of dietary restriction on the basal rate of somatotrope renewal in the pituitary gland. Bromodeoxyuridine (BrdU), a thymidine analog, was administered continuously for 1 week in male F344 rats at 3, 8 and 20 months of age (mo), fed ad libitum (AL) or diet restricted from 1.5 mo (DR). Combined immunostainings for BrdU and GH visualized newly formed somatotropes as well as pituitary cells in tissue sections. The rate of incorporation of BrdU by anterior pituitary cells (BrdU-labeled nuclei/100 nuclei) was not influenced by the dietary regimen or age. The fraction of BrdU-labeled somatotropes relative to all labeled cells precipitously decreased to the same level in both dietary groups between 3 and 8 mo, although the fraction was greater in DR rats at 3 mo. In AL rats, the fraction decreased further between 8 and 20 mo, while it stabilized in DR rats. Our results suggested that dietary restriction maintains the basal rate of somatotrope renewal in later life in male rats. Although one must also estimate the effects of dietary restriction on apoptotic cell death in pituitary cells, the present study provides evidence that dietary restriction modulates somatotropes cell turnover and preserves the cell population for GH secretion during aging.

The lymphopenia (lyp) gene controls the intrathymic cytokine ratio in congenic BioBreeding rats.

The lymphopenia gene (lyp) on rat chromosome 4 is closely linked to autoimmune diabetes in the BioBreeding (BB) rat. Lyp controls the number of peripheral lymphocytes by reducing T cells of the RT6+ phenotype by almost 90%. Following nine cycle of marker-assisted cross-intercross breeding we have developed congenic lyp/lyp, lyp/+ and +/+ (wildtype) rats on the background of DR rats. Prediabetic and insulitis free lyp/lyp, lyp/+ and +/+ rats were used to determine the effect of lyp on cytokine expression in the thymus. In situ hybridization of thymus cryosections showed that the interferon gamma (IFN gamma) mRNA expression was highest in lyp/lyp rats and the hybridization signal was restricted to the medullary compartment. The frequency of IFN gamma and interleukin (IL)-10 mRNA expressing cells in isolated thymocytes determined by quantitative image analysis, demonstrated an increased IFN gamma: IL-10 ratio in thymocytes from lyp/lyp homozygotes compared to lyp/+ and +/+ rats. This confirmed a lyp gene dose-dependent segregation of the IFN gamma high phenotype. Recombinant human glutamic acid decarboxylase (GAD65) increased the number of IFN gamma and IL-10 mRNA expressing thymocytes after in vitro culture. We conclude that the quantitative ratio of cytokine producing thymocytes is associated with the lyp genotype. These potentially autoreactive thymocytes may explain the establishment of beta-cell directed autoimmunity in the BB rat despite peripheral lymphopenia.

Endogenous inhibitor of Na-K-Cl cotransport system in inbred Dahl rats.

Dahl salt-sensitive (DS) rats seem characterized by a ubiquitous increase in Na-K-Cl cotransport activity. Here, an endogenous inhibitor of the Na-K-Cl cotransport system (cotransport inhibitory factor, CIF) was investigated in inbred Dahl salt-sensitive (DS) and salt-resistant (DR) rats. The animals were orally loaded for 10 days with 2% NaCl. Plasma from salt-loaded DS rats inhibited cotransport with a 50% inhibition concentration value (IC50) of 6.4 +/- 0.6% (% plasma concentration, vol/vol) vs. 24.2 +/- 2.2% in DR rats (P < 0.0001). In urine, IC50 for cotransport inhibition was constantly lower in DS before and all during the whole salt-loading period (after 10 days of salt loading, IC50 was 2.59 +/- 0.11% and 6.00 +/- 0.24% in DS and DR rats, respectively; P < 0.0001). After 3 days of salt loading, higher salt appetite in DS rats magnified the differences in urinary CIF excretion. In erythrocytes from DS rats, increased cotransport activity was strongly correlated with urinary CIF excretion (r = 0.967). In conclusion, DS rats present increased plasmatic and urinary CIF levels. This can be a compensatory phenomenon to reduce cotransport hyperactivity and increased NaCl reabsorption at the thick ascending limb of Henle's loop.

Effects of dietary salt on erythrocyte and renal Na,K-ATPase activity in Dahl salt-sensitive and salt-resistant rats

This study was designed to investigate the effects of dietary salt and potassium supplementation on blood pressure and the Na,K-ATPase activity in erythrocytes and renal cortex from Dahl salt-sensitive (DS) and salt-resistant (DR) rats. Rats were fed diets containing low salt (0.4%), high salt (7%) or high salt plus potassium-citrate (K-citrate, 3%) from 5 to 10 weeks of age or from 15 to 20 weeks of age. The systolic blood pressure of DS rats measured by the tail-cuff method was significantly increased by feeding the high salt or high salt plus K-citrate diets compared with rats fed the low salt diet at both ages. The DR rats remained normotensive regardless of the dietary salt level. Supplementation of the high salt diet with K-citrate attenuated elevation of blood pressure in DS rats. The sodium content of red blood cells of DS rats fed the high salt diet was increased whereas that of DR rats fed the same diet remained unchanged. The erythrocyte Na,K-ATPase activity was not altered at 10 weeks of age by dietary salt in both strains of rats. But at 20 weeks of age, the erythrocyte enzyme activity was suppressed in DS rats fed the high salt diet and was significantly lower compared with that in DR rats fed the same diet. The renal cortex microsomal enzyme activity was decreased in both of 10-week and 20-week old DS rats fed the high salt diet. The renal cortex enzyme activity in DR rats was not changed by dietary salt levels and consequently was greater than that of DS rats when fed the high salt diet. The renal cortex Na,K-ATPase activity of DS rats was negatively correlated to blood pressure. These results suggest that the permeability of cell membrane in DS rats is increased when fed the high salt diet and consequent increases in cell sodium concentration together with suppressed Na,K-pump activity are involved in the progressive increase in blood pressure.

Gluconeogenesis in the livers of diet-restricted rats--a 13C nuclear magnetic resonance study.

Gluconeogenic activity is reduced during starvation. However, it is less clear whether the utilization of gluconeogenic substrates is diminished with mild but prolonged diet restriction and, if so, whether there are intrinsic changes in the gluconeogenic pathway. We examined gluconeogenesis in the livers of diet-restricted rats with 13C nuclear magnetic resonance (NMR) spectroscopy. Fischer 344 rats were given 88% (DR group) of what was consumed by the weight-matched ad libitum-fed normal rats (CL group). At the end of 5 weeks, the removed livers were perfused with [3-13C] alanine while 13C NMR spectroscopy was performed. The final body and liver weights were the same for the two groups. In DR rats, both intrahepatic [3-13C] alanine and metabolites generated via pyruvate and oxaloacetate, including aspartate and carbamoyl aspartate, appeared in significantly reduced amounts. There was also marked diminution in the production of glucose. In the livers of DR rats, alanine uptake through System A transport, the fluxes through pyruvate carboxylase, the biosynthesis of pyrimidine nucleotides, and the production of glucose from alanine were all significantly decreased with mild intake restriction. Attenuated protein synthesis in the liver of diet-restricted animals may be the cause for this decreased utilization of alanine for gluconeogenesis.

Induction of high affinity epidermal growth factor binding in the aorta of Dahl hypertensive rats fed with high salt diet.

Dahl salt sensitive rats (DS) developed severe hypertension on four weeks of high salt feeding while the Dahl salt resistant rats (DR) remained normotensive under the same conditions. The specific maximal binding of epidermal growth factor (EGF) in the freshly prepared kidney membranes of high salt fed DS rats was higher than those from DR rats (5.3 +/- 1.9 vs. 1.6 +/- 0.62 fmoles/mg protein, p<0.001). Scatchard analysis of EGF binding in the kidney showed one class of receptors in the DR (K(d) = 0.75 +/- 0.05 nM) as well as in the DS rats (K(d)=0.69 +/- 0.06 nM). The EGF binding in the aortic membranes of DS rats was also high compared to DR rats (24.98 +/- 5.52 vs. 13.20 +/- 4.10 fmoles/mg protein, p < 0.001). Scatchard analysis of EGF binding in the aorta showed one class of receptors in the DR aorta with a K(d) of 0.70 +/- 0.06 nM. On the other hand, in the DS rat aorta two classes of receptors, a high affinity form (K(d)=0.05 +/- 0.01 nM) and a low affinity form (K(d)=3.5 +/- 0.3 nM) were noted. The induction of a high affinity species of EGF receptors in the aorta, appears to be a mechanism unique to the salt fed DS rats.

Blunted pressure natriuresis in ovariectomized Dahl-Iwai salt-sensitive rats.

Our objective was to determine whether increased salt sensitivity after menopause precedes the development of overt hypertension. We investigated the effect of ovariectomy on pressure natriuresis in Dahl-Iwai salt-sensitive (DS) and salt-resistant (DR) rats by in vivo perfusion studies. Differences in the neural and hormonal backgrounds of the kidney were minimized by renal denervation and by holding plasma vasopressin, aldosterone, corticosterone, and norepinephrine levels constant by intravenous infusion. The pressure-natriuresis relationship was blunted in DS rats compared with DR rats (slope, 0.30 versus 0.63 mumol.min-1.g kidney wt-1.mm Hg-1, P < .01). The impaired pressure-natriuresis response of DS rats was further blunted by ovariectomy (from 0.30 to 0.14 mumol.min-1.g kidney wt-1.mm Hg-1, P < .05), and that of DR rats was not. The ovariectomized DS rats developed hypertension earlier than sham-operated DS rats by salt loading. These results show that ovariectomy enhances genetic salt sensitivity by blunting the pressure-natriuresis relationship, which precedes the development of overt hypertension in female DS rats.

Effects of vasopressin V1 and V2 receptor antagonists on the development of salt-induced hypertension in Dahl rats.

To determine whether the vasopressor and antidiuretic actions of arginine vasopressin (AVP) may participate in the development of salt-induced hypertension, we examined the long-term effects of AVP V1 and V2 receptor antagonists on blood pressure (BP) in Dahl-Iwai salt-sensitive (DS) and salt-resistant (DR) rats. From age 7 weeks, DS and DR rats were fed a diet containing 8% NaCl, alone (control group); 8% NaCl and 1% OPC-21268 (V1 antagonist-treated group); or 8% NaCl and 0.05% OPC-31260 (V2 antagonist-treated group). The pressor response to AVP was significantly inhibited in DS rats treated with OPC-21268. Urinary volume and water intake were significantly increased by administration of OPC-31260; this increase was greater in DR rats than in DS rats. Indirect BP measurements obtained using tailcuff plethysmography showed that DS but not DR rats developed hypertension when fed high-salt diets. However, chronic treatment with either OPC-21268 or OPC-31260 did not alter the course of hypertension in DS rats, despite the effective blocking actions of these antagonists. This finding also was confirmed by direct BP measurements. Our results indicate that even if AVP plays a role in salt-induced hypertension peripheral blockade of either subtype of AVP receptors does not prevent the development of hypertension in DS rats.

Lenticular Alterations in Hypertensive Rats

Cataract development has been reported in Dahl salt-sensitive (DS) hypertensive rats with high-salt intake. An alteration in ionic transport and electrolyte balance has been reported to be associated with hypertension in these animals. A morphological evaluation of the lenses of salt-sensitive 'cataract-prone' (DS) and salt-resistant (DR) control animals is lacking. We undertook this investigation to evaluate changes in lenticular morphology and in systolic blood pressure (SBP) following administration of high-salt. Both DS and DR rats were given high-salt for up to 33 weeks. Lenses were extracted at desired intervals following the initiation of the high-salt diet and processed for light and transmission electron microscopy. Except for some variations between animals, our study showed that DR rats, in general, exhibited normal SBP and relatively normal morphology. In comparison, the lenses of DS hypertensive rats demonstrated the following major changes: (1) some epithelial cells showed multilayering, nodule formation, pyknotic nuclei, swelling of cell organelles, presence of a large number of lysosomes, and distension of intercellular spaces, (2) disorganization of the bow and (3) swelling of fiber cells in the equatorial region. These changes were similar to those observed in precataractous stages during the development of several types of experimentally induced cataracts and indicate an alteration in normal electrolyte balance as well as hyperosmolarity. Changes in ion transport and electrolyte imbalance have been reported in the lenses of DS rats on high-salt diet. These alterations and a defect in the sodium-potassium pump may be responsible for cataract development in these hypertensive rats.

Effects of Dietary Salt on Inhibition of Norepinephrine-Induced Contraction by Ryanodine and Verapamil in Isolated Aortic Rings from Dahl Rats.

Using ryanodine and verapamil, we compared the effects of dietary salt on the relative contribution of sarcoplasmic reticulum (SR) Ca2+ release and gated Ca2+ entry to arterial contractions induced by norepinephrine (NE) in Dahl salt-sensitive (DS) and salt-resistant (DR) rats. Aortic rings freshly excised from 14DS rats and 13DR rats that had been on low- (0.3%) or high- (8%) NaCl diets for 4 weeks were superfused with physiological saline and isometric tension was measured. The inhibition of the NE (3×10-8M) -induced contraction of aortic rings by ryanodine (3μM) was significantly greater in DR rats on the low-salt diet than in those on the high-salt diet (p<0.02), but there was no such difference in DS rats. The inhibition of the NE-induced contraction of aortic rings by verapamil (10μM) was significantly greater in DS rats on the high-salt diet than in those on the low-salt diet (p<0.02), but there was no such difference in DR rats. These observations suggest that the effects of dietary salt on gated Ca entry and SR Ca release in NE-induced contraction differ between DS and DR rats. They also suggest that gated Ca2+ entry might play an important role in Ca2+ control and that the mechanism by which Ca release from SR is reduced might be impaired, or that the ryanodine receptor might be altered in these tissues of salt-fed DS rats. These changes might lead to an elevation of intracellular calcium and contribute to the mechanism of hypertension. (Hypertens Res 1994; 17: 165-171)

Effects of a Calcium Channel Blocker, Nicardipine, on Pressure-Natriuresis in Dahl Salt-Sensitive Rats

The effects of a calcium channel blocker, nicardipine, on pressure-natriuresis responses were studied in Dahl salt sensitive (DS) and resistant (DR) rats. Differences in the neural and endocrine background were minimized by renal denervation and by holding plasma vasopressin, aldosterone, corticosterone, and norepinephrine levels constant by intravenous infusion. The renal plasma flow (RPF) and glomerular filtration rate (GFR) of DS rats were disautoregulated in the low renal perfusion pressure range, while those of DR rats were autoregulated. Administration of nicardipine (0.3 microgram/kg/min) into the renal artery significantly increased RPF and GFR and abolished the autoregulation in both strains of rats. Nicardipine also sharpened the pressure-natriuresis responses in both strains without changes in fractional excretion of sodium. These findings suggest that nicardipine increased GFR and thereby improved the pressure-natriuresis responses of DS rats.

The alpha 1 Na(+)-K+ pump of the Dahl salt-sensitive rat exhibits altered Na+ modulation of K+ transport in red blood cells.

The properties of the alpha 1 Na(+)-K+ pump were compared in Dahl salt-sensitive (DS) and salt-resistant (DR) strains by measuring ouabain-sensitive fluxes (mmol/liter cell x hr = FU, Mean +/- SE) in red blood cells (RBCs) and varying internal (i) and external (o) Na+ and K+ concentrations. Kinetic parameters of several modes of operation, i.e., Na+/K+, K+/K+, Na+/Na+ exchanges, were characterized and analyzed for curve-fitting using the Enzfitter computer program. In unidirectional flux studies (n = 12 rats of each strain) into fresh cells incubated in 140 mM Na(+) + 5 mM K+, ouabain-sensitive K+ influx was substantially lower in the DS than in DR RBCs, while ouabain-sensitive Na+ efflux and Nai were similar in both strains. Thus, the coupling ratio between unidirectional Na+:K+ fluxes was significantly higher in DS than in DR cells at similar RBC Na+ content. In the presence of 140 mM Nao, activation of ouabain-sensitive K+ influx by Ko had a lower Km and Vmax in DS as estimated by the Garay equation (N = 2.70 +/- 0.33, Km 0.74 +/- 0.09 mM; Vmax 2.87 +/- 0.09 FU) than in DR rats (N = 1.23 +/- 0.36, Km 2.31 +/- 0.16 mM; Vmax 5.70 +/- 0.52 FU). However, the two kinetic parameters were similar following Nao removal. The activation of ouabain-sensitive K+ influx by Nai had significantly lower Vmax in DS (9.3 +/- 0.4 FU) than in DR (14.5 +/- 0.6 FU) RBCs but similar Km. These data suggest that the low K+ influx in DS cells is caused by a defect in modulation by Nao and Nai. Na+ efflux showed no differences in Nai activation or trans effects by Nao and Ko, thus accounting for the different Na+:K+ coupling ratio in the Dahl strains. Further evidence for the differences in the coupling of ouabain-sensitive fluxes was found in studies of net Na+ and K+ fluxes, where the net ouabain-sensitive Na+ losses showed similar magnitudes in the two Dahl strains while the net ouabain-sensitive K+ gains were significantly greater in the DR than the DS RBCs. Ouabain-sensitive Na+ influx and K+ efflux were also measured in these rat RBCs. The inhibition of ouabain-sensitive Na+ influx by Ko was fully competitive for the DS but not for the DR pumps. Thus, for DR pumps, Ko could activate higher K+ influx in DR pumps without a complete inhibition of ouabain-sensitive Na+ influx.(ABSTRACT TRUNCATED AT 400 WORDS)

Dahl's salt-resistant normotensive rat has mutations in cytochrome P450(11 beta), but the salt-sensitive hypertensive rat does not.

Molecular cloning of cytochrome P450(11 beta) cDNAs from the adrenal glands of Dahl's salt-sensitive hypertensive (DS) and salt-resistant normotensive (DR) rats was performed using a combined technique of the first strand cDNA synthesis by reverse transcriptase followed by polymerase chain reaction. The cDNA sequence of P450(11 beta)-DS was identical to that of wild type P450(11 beta). In contrast, the clone obtained from the DR rat contained six nucleotide substitutions causing five amino acid alterations (Arg-127-->Cys, Val-351-->Ala, Val-381-->Leu, Ile-384-->Leu, and Val-443-->Met). When the two cDNAs were expressed in COS-7 cells and steroid conversion rates of the transformed cells were determined, a ratio of 18-hydroxylation to 11 beta-hydroxylation of 11-deoxycorticosterone by P450(11 beta)-DS-expressed cells was 0.58, whereas that by P450(11 beta)-DR-expressed cells was 0.23. Plasma levels of 18-hydroxy-11-deoxycorticosterone and corticosterone (the 11 beta-hydroxylation product of 11-deoxycorticosterone) in DS and DR rats well reflected the steroidogenic activities of the two P450s. These results suggest that the characteristic plasma steroid level of the DR rat is caused by the mutations in P450(11 beta) gene and may act to maintain the normotensive blood pressure in this rat strain during sodium loading.

High-salt diet upregulates activity and mRNA of renal Na(+)-K(+)-ATPase in Dahl salt-sensitive rats

We examined the effect of a high-salt (HS) diet on the regulation of renal cortical Na(+)-K(+)-adenosinetriphosphatase (Na(+)-K(+)-ATPase) in young Dahl salt-sensitive (DS) and salt-resistant (DR) rats. The activity of Na(+)-K(+)-ATPase, determined in permeabilized proximal tubule segments, was similar in DS and DR rats on normal salt (NS) diet. HS diet resulted in a twofold increase in proximal tubule Na(+)-K(+)-ATPase activity in DS rats but not in DR rats. The mRNA abundance, which was also similar in DS and DR rats on NS diet, increased after 2 days on HS diet in both innervated and denervated kidneys from DS rats but had no effect in DR rats. The activity of Na(+)-K(+)-ATPase and the content of alpha 1- and beta-protein in cortical homogenate were similar in DS and DR rats on both NS and HS diets. Treatment with benserazide, an inhibitor of dopa decarboxylase, upregulated proximal tubule Na(+)-K(+)-ATPase activity and increased Na(+)-K(+)-ATPase mRNA in DR rats on HS diet. Taken together, these data indicate that there is a primary defect in the dynamic hormonal regulation of Na(+)-K(+)-ATPase activity in intact tubular cells, which might stimulate Na(+)-K(+)-ATPase transcription.

T lymphocytes capable of activating endothelial cells in vitro are present in rats with autoimmune diabetes.

Endothelial activation as evidenced by increased expression of leukocyte adhesion molecules occurs during immune-mediated inflammatory processes. One such process is insulitis, the pancreatic islet inflammation that leads to autoimmune insulin-dependent diabetes mellitus (IDDM). To determine if the induction of IDDM correlates with the presence of T lymphocytes capable of activating endothelial cells (EC), we studied the diabetes resistant BB (DR) rat. These animals become diabetic after in vivo depletion of T cells expressing the RT6 alloantigen. Various populations of purified DR T lymphocytes were cocultured with MHC compatible rat EC. We observed: 1) RT6- T cells from diabetic animals induced maximal endothelial MHC Ag expression. 2) The ability of RT6- T cells to activate EC increased with the duration of in vivo RT6 depletion. It was acquired before the onset of insulitis but subsided after the onset of diabetes. 3) In contrast, neither unsorted total T cells nor in vitro-purified RT6- T cells activated EC. 4) Older DR rats depleted of RT6+ T cells did not become diabetic and their RT6- T cells did not activate EC. 5) T cell IFN-gamma production correlated with the intensity of EC activation. 6) direct T cell-EC contact was required for maximal IFN-gamma production and EC activation. We conclude that RT6- T cells capable of activating EC are generated during the induction of IDDM in DR rats. We hypothesize that such T cell activity may lead to endothelial activation in vivo and contribute to immune-mediated insulitis, beta-cell destruction, and IDDM.

Alterations of K+ transport by the alpha 1 Na(+)-K+ pump in red blood cells of the Dahl salt-sensitive rat.

We studied the kinetic properties of the Na(+)-K+ pump in rat red blood cells (RBCs) of the Dahl salt-sensitive (DS) and salt-resistant (DR) strains by measuring unidirectional ouabain-sensitive (OS) Na+ and K+ fluxes (mmol/L cell x h = FU, mean +/- SE) and varying internal (i) and external (o) Na+ and K+ concentrations. OS Na+ efflux into Nao 140 mM, Ko 5 mM was similar in both strains in fresh cells as well as for Vmax and Km for Nai. However, DS pumps have significantly lower K+ influx than DR pumps in fresh cells, thereby giving rise to a higher Na:K coupling ratio. The lower rates of K+ influx were caused by a defective activation by Nai and Nao that led to significantly lower Vmax than in DR pumps. The activation of K+ influx by Ko in the presence of 140 mM Nao had a lower Vmax and a higher affinity in DS (Vmax 2.58 +/- 0.09 FU, n = 17, Km 0.63 +/- 0.23 mM) than in DR rats (Vmax 4.7 +/- 0.3 FU, n = 16; Km 1.9 +/- 0.2 mM). However, when Nao was removed, these two kinetic parameters became similar in both strains. OS 86Rb/K efflux from fresh RBCs was significantly higher in DS than in DR rats, because the K50 from Nai inhibition was threefold higher in DS pumps. In summary, the low rates of unidirectional and net K+ influx in DS cells are caused by impaired Nai and Nao activation as well as the high values of K+ efflux are caused by low affinity for Nai inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)