Sodium-depleted Rats Research Articles

Rapid elicitation of salt appetite by an intravenous infusion of angiotensin II in rats.

A role for the renal renin-angiotensin system in the direct stimulation of salt appetite in the rat remains controversial because attempts to elicit the behavior by intravenous administration of angiotensin II (ANG II) have been unconvincing. We recently demonstrated that depletion-induced salt appetite was attenuated by selective blockade of peripheral ANG II synthesis with an intravenous dose of converting enzyme inhibitor [captopril (Cap)] that does not block the synthesis of ANG II inside the blood brain barrier. We now show that intravenous ANG II at 30 ng/min rapidly reestablishes salt appetite in Cap-blocked rats. The mean arterial blood pressure (MAP) of unblocked, sodium-depleted rats was normal, but Cap-blocked, depleted rats had low MAP. An intravenous infusion of ANG II in Cap-blocked rats brought MAP into the normal range and elicited water and salt drinking within 90 min. Phenylephrine also normalized MAP but failed to elicit fluid intake in Cap-blocked, sodium-deficient rats. Sodium and water balances tended to be more positive during ANG II than during phenylephrine infusions. Thus circulating ANG II may stimulate both thirst and salt appetite by a direct action on the brain and not by causing natriuresis or by raising the blood pressure.

Chronic Kinin Blockade and Effect of Ramipril in Renal Adaptation to Sodium Restriction

The contribution of endogenous kinins to impairment in renal adaptation to a 6-day period of dietary sodium withdrawal associated with treatment with ramipril (5 mg/kg per day) and losartan (30 mg/kg per day) was evaluated by use of concomitant chronic administration of the bradykinin B2-receptor antagonist Hoe 140 (150 or 300 micrograms/kg per day via subcutaneous osmotic pump). A similar level of higher cumulative sodium excretion was observed in ramipril- and losartan-treated rats compared with untreated animals, and the effect of ramipril was not affected by Hoe 140. Similarly, the fall in arterial pressure and the renal vasodilatation associated with ramipril and losartan were not modified by Hoe 140. Glomerular filtration rate (785 +/- 73 microL/min per g KW in untreated sodium-depleted rats) decreased to a larger extent in ramipril-treated rats compared with losartan-treated rats (371 +/- 78 and 550 +/- 55 microL/min per g KW, respectively). Hoe 140 markedly prevented the alteration in glomerular filtration rate associated with ramipril, thus resulting in a final glomerular filtration rate (543 +/- 41 microL/min per g KW) similar to that observed with losartan. These findings demonstrate that despite a lack of influence on arterial pressure and sodium balance, accumulation of kinins markedly contributes to deterioration of the glomerular filtration rate induced by ramipril in sodium-depleted rats.

Diphenylpropionic acids as new AT1 selective angiotensin II antagonists.

The synthesis and pharmacological evaluation of a new series of potent AT1 selective diphenylpropionic acid nonpeptide angiotensin II receptor antagonists are reported. The new compounds were evaluated for in vitro AT1 (rat liver) and AT2 (rat adrenal) binding affinity as well as for in vivo inhibition of angiotensin II-induced increase in mean arterial blood pressure in pithed rats. Unsaturation of the diphenylpropionic acids as well as substitution or replacement by alkyl groups of the pendant phenyl ring resulted in a decrease of potency. On the other hand, the presence of small alkyl groups in the alpha-position to the carboxylic acid was important for activity, with one of the resultant diastereoisomers (R*,R*) being ca. 10-fold more active than the other (R*,S*). Oral evaluation of the most active compounds in a furosemide-treated sodium-depleted rat model showed that compound 36g (UR-7198) reduced blood pressure dose dependently. This compound showed in vitro and iv potencies similar to that of the reference compound losartan but faster onset of action and somewhat greater oral activity, presumably due to its improved bioavailability.

Glossopharyngeal nerve transection does not compromise the specificity of taste-guided sodium appetite in rats

The chorda tympani nerve (CT) has been shown to be critical in the sodium-specific drinking behavior of sodium-depleted rats, but the role of other gustatory nerves and the contribution of the major salivary glands remain to be elucidated. In this study, rats received either bilateral section of the CT (CTX) or the glossopharyngeal nerve (GLX), extirpation of the sublingual and submaxillary salivary glands (DSAL), or sham surgery. After recovery, rats were sodium depleted with furosemide and tested for their licking responses to 0.05 and 0.3 M NaCl, KCl, CaCl2, and NH4Cl, as well as distilled water in an automated gustometer. Rats that received GLX maintained a specific sodium appetite comparable to controls despite denervation of approximately 64% of the taste buds. In contrast, compared with control rats, CTX and DSAL rats had altered response profiles, showing much smaller differences in licking to NaCl relative to the other stimuli. This was accompanied by a substantially lower lick rate in DSAL rats, raising the possibility that general licking impairments contributed to the decreased NaCl responsiveness in these rats. These findings imply that the CT, but not the glossopharyngeal nerve, is necessary for the maintenance of normal sodium-specific, taste-guided behavior under sodium deplete conditions.

Preference for nacl solutions in sham drinking Sprague-Dawley rats: Water deprivation, sodium depletion, and angiotensin II

Male Sprague-Dawley rats were fitted with closable gastric fistulas and were then tested under closed fistula (real intake) and open fistula (sham intake-fluids drain from the stomach without appreciable absorption) conditions in one of three states: fluid deprivation, sodium depletion, and infusion of angiotensin (Ang) II. Water and various concentrations of NaCl were offered to drink in 1-h one- or two-bottle intake tests. In Experiment 1, water-deprived rats with closed fistulas drank more 0.15 M NaCl than either water or 0.3 M NaCl, offered in one-bottle tests. In sham drinking tests, the intake decreased monotonically as NaCl concentration increased. In two-bottle tests, water was greatly preferred over NaCl solutions. In Experiment 2, sodium-depleted rats preferred NaCl over water, again demonstrating a peak intake at 0.15 M in closed fistula conditions. However, with the fistula open the intakes of 0.05 and 0.15 M were similar, and 0.45 M considerably lower. In Experiment 3, Ang II-infused rats consumed both water and NaCl in two-bottle tests in both open and closed fistula trials. The quantity ingested on sham trials was only modestly elevated over real intake trials with Ang lI compared with sham tests in Experiments 1 and 2.

Physiologic Role of ETA Receptors in the Regulation of Renal Hemodynamics in Normal and Salt-Depleted Rats

Exogenous endothelin (ET) promotes powerful vasoconstriction in systemic and renal microcirculation. However, the physiologic role of endogenous ET on the moment-to-moment regulation of the circulation remains unclear. We investigated the effects of acute administration of FR139317, a nonpeptide inhibitor specific for the ETA receptor shown in preliminary experiments to reverse the established vasoconstrictor effects of exogenous ET. Renal and glomerular functional parameters were determined in eight anesthetized adult male Munich-Wistar rats receiving a standard diet (0.5% Na) before and after bolus injection of FR139317, 10 mg/kg. To assess the physiologic role of ET in sodium depletion, eight rats received a low-salt (0.06% Na) diet for 2 weeks before acute FR139317 treatment. Eight additional salt-restricted rats received a bolus injection of the angiotensin II inhibitor losartan, 10 mg/kg i.v., as a positive control. FR139317 exerted no detectable microcirculatory effect in rats receiving standard diet. In sodium-depleted rats, losartan lowered blood pressure by 12 mm Hg, raised heart rate by 20 beats/min, and decreased renal vascular resistance by 33%. By contrast, FR139317 had only slight hemodynamic effects, although it increased heart rate by 15 beats/min. These results suggest that ET does not participate, at least via ETA receptors, in the regulation of renal and systemic microcirculation in the rat. However, it may be involved in the circulatory adaptations to chronic sodium depletion. A regulatory role for ET via ETB receptors is also possible.

Different homologous subunits of the amiloride-sensitive Na+ channel are differently regulated by aldosterone.

Long term regulation of the amiloride-sensitive Na+ channel activity by steroid hormones occurs via de novo protein synthesis. The messenger level of RCNaCh1, previously shown by expression cloning to be a component of this channel, was measured in colons from rats fed with a low sodium diet. After 1 week of this diet, the channel activity was increased in an all-or-none fashion, whereas the level of RCNaCh1 messenger remained constant. A cDNA coding for another subunit of the Na+ channel was obtained by polymerase chain reaction. The 650-amino acid protein, entitled RCNaCh2, is 58% homologous to RCNaCh1 and displays a similar structure. It had no intrinsic activity when expressed alone in Xenopus oocytes, but its co-expression with RCNaCh1 increased the channel activity 18 +/- 5-fold. The increase in messenger level for RCNaCh2 during the time course of the diet is likely to explain the positive regulation of the rat colon Na+ channel by steroids. Immunocytochemical localization of the RCNaCh1 subunit revealed an apical labeling in colon from sodium-depleted rats. No labeling was observed in colon from control animals. These results suggest that oligomerization is needed for the proper expression of RCNaCh1 at the cell surface.

Differential changes in central monoaminergic metabolism during first and multiple sodium depletions in rats

To investigate the role of central monoamines in the behavior of sodium appetite, serotonergic and dopaminergic metabolism in regions of the forebrain and dorsal hindbrain were measured in sodium-depleted rats. Male Sprague-Dawley rats were sodium depleted by injection of the diuretic-natriuretic drug, Lasix (furosemide, 10 mg), and maintained on a sodium-deficient diet overnight. Rats were tested at at first sodium depletions. There were three test conditions: 1) mock depletion consisted of vehicle injection and overnight sodium-deficient diet; 2) sodium depletion alone consisted of Lasix injection and overnight sodium-deficient diet; and 3) intake of NaCl following sodium depletion consisted of 9-min access to 0.3 M NaCl after Lasix injection and overnight sodium-deficient diet. Dopamine (DA), DOPAC, HVA, 5-HT, and 5-HIAA were measured by HPLC in the olfactory tubercle, amygdala-pyriform lobe, n. accumbens, hypthalamus, caudate nucleus, and the dorsal hindbrain. Ingestion of 0.3 M NaCl for 9 min after the first sodium depletion increased 5-HIAA/5-HT ratio significantly in the n. accumbens and amygdala, and increased DOPAC/DA ratio in the n. accumbens and olfactory tubercle compared to the mock treatment. In contrast to the results after the first sodium depletion, rats that ingested 0.3 M NaCl after four or more sodium depletions had no changes in 5-HT and DA metabolism in the forebrain, but they did have a significantly larger 5-HIAA/5-HT ratio in the dorsal hindbrain than mock-treated rats. These results suggest that release of DA and 5-HT in the limbiic forebrain regions may be important for the behavioral and neuroendocrine responses to the initial sodium depletion, but not to subsequent depletions. Alternatively, the changes in monoamine metabolism after the first sodium depletion may be due to the stress of that sodium depletion.

The effect of chronic sodium depletion on renal function in conscious rats.

In order to investigate the effect of chronic sodium depletion on renal proximal tubular reabsorption, studies were performed in conscious, unrestrained Brattleboro rats. Since these animals lack circulating vasopressin, fractional water reabsorption in the distal nephron can be assumed to be constant and changes in urine flow rate should therefore reflect changes in end-proximal fluid delivery. Sodium depletion was induced by placing rats on a low-sodium diet (4 mmol Na (kg dry wt)-1) and administering frusemide (40 mg (kg body wt)-1) by gavage on the first 2 days. Extracellular volume, measured after 7-9 days, was reduced by 19% (P < 0.02) as compared with that of rats maintained on a control diet. Urine flow rate, measured during days 4-7 of the low-sodium diet, was significantly lower than that of control rats (142 +/- 8 vs. 168 +/- 5 ml day-1, P < 0.01). Since renal papillary interstitial fluid osmolality was found to be reduced in the sodium-depleted rats (693 +/- 38 vs. 812 +/- 36 mosmol (kg H2O)-1, P < 0.05), it is unlikely that water reabsorption from sites beyond the proximal tubule had increased. The observed reduction in urine flow rate therefore strongly suggests a reduction in end-proximal fluid delivery. In the second part of the study, a single group of Brattleboro rats was used, in which osmotic minipumps were implanted in the peritoneal cavity for continuous infusion of [14C]inulin. After recovery from the operation, the rats were maintained on a control diet for 6 days (pre-control period), then subjected to sodium depletion (low-sodium diet for 6 days, frusemide administration on the first 2 days), and finally returned to the control diet for 6 days, with access to 0.46 M NaCl solution on the first 2 days, in order to restore sodium balance (post-control period). On the final 2 days of each phase, urine flow rate and [14C]inulin clearance (= glomerular filtration rate, GFR) were measured. Urine flow rates during the pre-control, sodium depletion and post-control periods were 169 +/- 7, 132 +/- 8 (P < 0.001) and 176 +/- 8 microliters min-1, respectively; corresponding values for fractional water excretion were 7.0 +/- 0.3, 6.0 +/- 0.5 (P < 0.01) and 7.4 +/- 0.4%. Only a small reduction GFR, of borderline statistical significance, was observed during sodium depletion.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II: endothelium-derived nitric oxide interaction in conscious rats.

In anesthetized rats, renal perfusion is largely regulated by a balance between the vasodilator influence of endothelium-derived nitric oxide (EDNO) and angiotensin II (AII)-mediated vasoconstriction. However, in conscious rats, which are characterized by lower PRA, the influence of AII is largely dissipated. To determine whether chronically increasing PRA enhances the interaction between AII and EDNO in regulating renal perfusion, radioactive microspheres were used to assess RBF in conscious sodium-depleted rats. PRA of control rats on a standard diet was 2.3 +/- 0.3 ng of AI/mL per hour compared with 16.8 +/- 1.5 ng of AI/mL per hour (P < 0.001) for rats on a sodium-restricted diet. In 12 rats on a standard diet, the inhibition of EDNO synthesis with L-Nw-nitroarginine methyl ester (L-NAME) increased blood pressure (BP) from 111 +/- 2 to 135 +/- 3 (P < 0.001) and decreased RBF by 47% (from 8.0 +/- 0.6 to 4.3 +/- 0.3 mL/min per gram kidney wt; P < 0.001). Renal vascular resistance (RVR) increased by 132% (from 14.9 +/- 1.2 to 34.7 +/- 3.3 resistance units (RU); P < 0.001). Pretreatment with Losartan, an AII receptor antagonist, did not modify the changes in BP, RBF, and RVR induced by L-NAME.(ABSTRACT TRUNCATED AT 250 WORDS)

ENHANCEMENT OF FK506 NEPHROTOXICITY BY SODIUM DEPLETION IN AN EXPERIMENTAL RAT MODEL

FK506 can show efficacy in transplant rejection even after other immunosuppressive drugs have been ineffective. However, the lack of a suitable animal model has hindered the study of FK nephrotoxicity, which has been noted as a common adverse effect in human trials. In this paper, we report a model of chronic FK nephrotoxicity in which renal structure and function are worsened by sodium depletion. Pair-fed male Sprague-Dawley rats were given FK (6 mg/kg p.o.) or vehicle for 21 days on a low-salt or normal diet. There was no significant difference in body weight between FK and vehicle groups. The FK whole-blood trough levels (3-10 ng/ml) in rats are similar to those in FK treated transplant patients. In sodium-depleted rats, FK clearly decreased GFR (0.09 +/- 0.03 ml/min/100 g vs. 0.94 +/- 0.06 ml/min/100 g in the vehicle group, P < 0.01), urinary osmolarity (UOsm, P < 0.01) and plasma magnesium (P < 0.01) and increased plasma creatinine (Pcr, P < 0.01), fractional excretion of magnesium (P < 0.01), urine volume (P < 0.01), plasma renin activity (PRA, P < 0.05), and alanine aminopeptidase (AAP, P < 0.05) as compared with those in the vehicle group. Salt depletion significantly potentiated these functional changes as compared with those in the normal salt group (GFR, UOsm, Pcr, PRA, and AAP of the low salt group vs. those of the normal salt group, P < 0.05 by ANOVA). In the sodium-depleted rats, the main lesion in the rat kidneys was focal collapse and vacuolization in proximal tubules, but there was also significant interstitial fibrosis. In contrast, no injury was observed in the sodium-replete rat kidneys. In conclusion, an experimental model of FK nephrotoxicity in sodium-depleted rats has been developed that is characterized by reduced GFR and structural damage to the proximal tubule accompanied by interstitial fibrosis. Sodium depletion appears to potentiate these changes at blood levels similar to those achieved in patients receiving FK.

Renal actions of the selective angiotensin AT 2 receptor ligands CGP 42112B and PD 123319 in the sodium-depleted rat

The purpose of this study was to investigate the renal actions of the new selective angiotensin AT 2 receptor ligands, CGP 42112B and PD 123319, in comparison to those of the AT 1 receptor antagonist losartan, in the sodium-depleted, anesthetized rat. Losartan (1, 3 and 10 mg/kg i.v.) produced a dose-dependent decrease in blood pressure and renal vascular resistance that was statistically significant. Effective renal blood flow tended to increase in response to all doses of losartan while glomerula filtration rate either did not change or decreased, leading to a significant fall in filtration fraction. Losartan did not induce significant changes in urine volume, urinary sodium excretion, urinary potassium excretion or free water formation. The selective AT 2 receptor ligand CGP 42112B at infusion rates of 1–100 μg/kg per min i.v. had no significant effect on blood pressure or any measured parameter of renal function. However, when infused at 1000 μg/kg per min i.v., CGP 42112B did not affect blood pressure, but significantly increased effective renal blood flow, glomerular filtration rate, urinary sodium excretion, urinary potassium excretion and free water formation, while significantly decreasing renal vascular resistance. The selective AT 2 receptor ligand PD 123319 at infusion rates between 1 and 100 μg/kg per min i.v. also had no significant effect on blood pressure or on any measured parameter of renal function. However, at an infusion rate of 1000 μg/kg per min i.v., PD 123319 tended to increase renal vascular resistance, urinary sodium excretion, urinary potassium excretion and free water formation, and to decrease effective renal blood flow, although none of these changes reached a level of statistical significance. Based upon the published affinities of CGP 42112B and PD 123319 for AT 1 and AT 2 receptors, plasma levels of either compound after infusion at rates between 1 and 1000 μg/kg per min would be compatible with an interaction with AT 2 receptors. However, at infusion rates of 1000 μg/kg per min, an interaction with AT 1 receptors could be expected. The data demonstrate that the new AT 2 receptor ligands PD 123319 and CGP 42112B either have little effect on renal function or, at high doses, have actions which might be indirect or explained by an interaction with AT 1 receptors. The results therefore support a role for AT 1 but not AT 2 receptors in the control of renal function in the sodium-depleted, anesthetized rat.

Chorda tympani section decreases the cation specificity of depletion-induced sodium appetite in rats.

Rats depleted of sodium by diuretic treatment were tested for their ability to respond selectively to NaCl after chorda tympani nerve (CTn) section (CTX). A variety of chloride salts (NaCl, KCl, NH4Cl, CaCl2) at two concentrations (0.05 and 0.3 M) were presented semirandomly to sodium-deplete rats in repeated single-stimulus trials (10 s). The responses of sodium-depleted surgical control rats (n = 8) were highly cation specific. These rats licked substantially more for both sodium stimuli than for any other chloride salt. On the other hand, the licking responses of CTX sodium-depleted rats (n = 8) were less cation selective. These rats licked NaCl and 0.05 M KCl at comparable rates. For both NaCl concentrations, CTX rats had significantly lower lick rates than controls. In addition, the difference between the lick rate for NaCl and that for the other salts was much greater for control rats than for CTX rats. Although CTn section did not entirely eliminate the high levels of responsivity to NaCl observed in the intact sodium-depleted rat, it did substantially compromise the selectivity of the behavior, which suggests that the input of the CTn is critical for taste-guided sodium specific behaviors.

Mucosal ouabain and Na+ inhibit active Rb+(K+) absorption in normal and sodium-depleted rat distal colon

To determine the effect of mucosal sodium and mucosal ouabain on active Rb+(K+) absorption, unidirectional and net 86Rb+ fluxes were measured under voltage-clamp conditions in the distal colon of normal and sodium-depleted rats. The role of mucosal sodium (independent of serosal sodium) was evaluated in a model of Rb+(K+) absorption in which serosal ouabain markedly enhanced active Rb+(K+) absorption. In normal rats, mucosal sodium was a competitive inhibitor of Rb+(K+) absorption, and Rb+(K+) absorption consisted of a mucosal sodium-sensitive component and a mucosal sodium-insensitive component. Further, mucosal ouabain almost completely inhibited the mucosal sodium-insensitive component but did not affect the mucosal sodium-sensitive component. In sodium-depleted rats, both mucosal sodium-sensitive and mucosal sodium-insensitive fractions of Rb+(K+) absorption were also identified. Aldosterone markedly stimulated the mucosal sodium-sensitive component (1.68 ± 0.15 vs. 0.60 ± 0.10 μEq · h−1 · cm−2) but not the sodium-insensitive component (0.88 ± 0.09 vs. 0.64 ± 0.06 μEq · h−1 · cm−2) component of Rb+(K+) absorption; however, in contrast to normal animals, mucosal sodium in sodium-depleted animals was a noncompetitive inhibitor of Rb+(K+) absorption. The mucosal sodium-insensitive component of Rb+(K+) absorption in sodium-depleted animals was substantially inhibited by mucosal ouabain, but the mucosal sodium-sensitive component, unlike that in normal animals, was partially inhibited by mucosal ouabain. These studies indicate that the characteristics of the Rb+(K+) absorptive process in sodium-depleted animals differ significantly from those present in normal animals, suggesting that aldosterone induces an Rb+(K+) absorptive mechanism not present in normal animals.

Sodium appetite after transection of the chorda tympani nerve in Wistar and Fischer 344 rats.

Acute sodium depletion in rats leads to dramatic increases in intake of hypertonic NaCl solutions, a behavior known as sodium appetite. The importance of signals conveyed by the chorda tympani (CT) nerve to the expression of sodium appetite is unclear. We examined the effects of bilateral CT transection on the short- and long-term response to sodium depletion in Wistar and Fischer 344 (F344) rat strains, because Wistar rats normally display a NaCl preference in the absence of need whereas F344 rats avoid NaCl. In both strains, sodium appetite after CT transection and treatment with the diuretic furosemide was delayed and blunted or eliminated. The results suggest that signals conveyed by the CT nerve are important in the expression of a sodium appetite. Effects on F344 rats are particularly interesting because CT transection surgery appears to have opposite effects on NaCl intake depending on whether F344 rats are sodium replete or deplete.

PH dependence of inhibition of arginine vasopressin-induced adenosine 3',5'-monophosphate production by cellular sodium depletion in rat renal inner medullary collecting duct cells in culture

pH dependence of inhibition of arginine vasopressin-induced adenosine 3',5'-monophosphate production by cellular sodium depletion in rat renal inner medullary collecting duct cells in culture

Amiloride sensitivity of the chorda tympani response to sodium chloride in sodium-depleted Wistar rats.

Peripheral gustatory mechanisms that may contribute to the expression of sodium (Na) appetite have been a focus of interest for many years. Because amiloride-sensitive Na transport is involved in the generation of neural signals in response to NaCl stimulation, the present study assessed whether changes in amiloride sensitivity of the neural response to NaCl accompany the induction of a Na appetite in the rat. Na deprivation was achieved by acute depletion with the diuretic furosemide. The magnitude of the whole-nerve chorda tympani response to 0.5 M NaCl was reduced in Na-depleted, compared with Na-replete, rats, which provides qualified support for previous reports that the induction of a Na appetite is associated with reduced neural responses to NaCl. However, changes in sensitivity to the specific Na channel blocker amiloride hydrochloride as a result of Na depletion were not evident. These findings suggest that the behavioral and neural changes that occur after Na depletion are not based on changes in amiloride sensitivity in the taste bud.

Effect of the prostacyclin analogue iloprost in sodium-depleted rats pretreated with captopril

Previous studies have shown that administration of captopril to sodium-depleted rats decreases the glomerular filtration rate (GFR) and blunts the increase in glomerular prostacyclin synthesis normally occurring in response to sodium depletion. To clarify the relationship between these two responses, iloprost, a stable analogue of prostacyclin, was administered to Na-depleted, captopril-treated (LNC) rats. At a dosage not affecting systemic blood pressure (12.5 ng/kg/min), iloprost increased GFR in LNC rats by 25% (from 0.26 ± 0.03 to 0.35 ± 0.03 ml/min100 g body wt, P < 0.01), without significant effects on renal plasma flow. No effect was observed in control rats. The results suggest that altered prostacyclin synthesis could contribute to the decrease of GFR in this model.

The effect of sodium repletion on growth and protein turnover in sodium-depleted rats

This study examines the consequences of sodium chloride supplementation to young rats previously made salt deficient by feeding them a sodium-deficient, chloride-replete diet. Salt-deficient rats received the test diet and distilled water for 10 days. As in our previous studies, rats cared for in this manner grew more slowly than rats fed the identical diet but allowed to drink 37 mM sodium chloride. On day 11, half of the salt-depleted animals received 37 mM sodium chloride in their drinking water. Sodium-deficient and supplemented rats were studied 1,2,5-6 and 11-12 days later. Urinary sodium rapidly rose from undetectable of 46 mEq/l urine within 1 day of supplementation and there was no further increase the next day, suggesting that extracellular fluid volumes were rapidly repleted. Food intake increased in the supplemented rats compared with the deficient animals but the difference in food intake equalled only 2.25 g/day for the first 2 days of supplementation. Over the last 12 days of the study, the slopes of both weight and length gains were equal in both the supplemented and the control group and significantly higher than those in the deficient rats. Over the course of the study, full catchup was not obtained in either length or weight. In addition to total weight and length gains, liver and kidney weights increased proportionately and by 5-6 days of supplementation were equivalent to the weights seen in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of rat adrenal messenger RNA and protein levels for cytochrome P-450s and adrenodoxin by dietary sodium depletion or potassium intake

The effect of low sodium and high potassium intake on rat adrenal zona glomerulosa (ZG) and zona fasciculata-reticularis (ZFR) were studied during a 7-day period, by analyzing mRNA and protein levels of various enzymes involved in aldosterone synthesis. In ZG significant increases in cytochrome P-450scc, P-450c21, P-450(11 beta), adrenodoxin mRNA and protein levels were observed after 2 days with either diet, and at day 7 these levels were further increased. The largest mRNA induction was observed at day 7 in sodium-depleted rats for P-450(11 beta), with a 4-fold increase, followed by 2.7- and 2.0-fold increases for P-450scc and P-450c21, respectively. A pattern similar to those of P-450scc and P-450(11 beta) was observed for adrenodoxin with a 2.1-fold increase after 7 days of Na+ restriction. In K(+)-loaded rats mRNA levels for P-450scc, P-450(11 beta), P-450c21, and adrenodoxin were also increased by 2.2-, 2.1-, 1.5-, and 1.9-fold respectively. Protein levels of these enzymes were also measured in ZG and showed increases similar to those of their respective mRNAs for both treatments. On the other hand, mRNA levels of P-450scc, P-450(11 beta), P-450c21, and adrenodoxin in ZFR were found significantly lower than in ZG, although they were slightly increased for both treated groups of rats as compared with controls. In addition, ZFR protein levels of corresponding enzymes did not fluctuate significantly under both ionic regimens. In conclusion, both low sodium and high potassium intakes act primarily on ZG. Their action on plasma aldosterone seems to be mediated by increasing both mRNA and protein and levels of steroidogenic enzymes, especially at the early step (cytochrome P-450scc) and even more at the late steps (cytochrome P-450(11 beta]. In addition, a close relationship appears to exist between the two mitochondrial P-450s and their electron donor adrenodoxin, since their mRNA and protein levels were similarly enhanced for both diets used.