Effects of sodium intake on albumin excretion in patients with diabetic nephropathy treated with long-acting calcium antagonists

OBJECTIVE

To determine whether sodium intake alters albumin excretion in patients with nephropathy from non-insulin-dependent diabetes mellitus who were treated with two different long-acting calcium antagonists.

DESIGN

Prospective, crossover, open-label trial.

SETTING

Rush-Presbyterian-St. Luke's Medical Center.

PATIENTS

9 men and 6 women (mean age +/- SD, 56 +/- 8 years) with non-insulin-dependent diabetes mellitus, hypertension, renal insufficiency, and macroalbuminuria.

INTERVENTION

Diltiazem (mean dose, 392 +/- 27 mg/d) or nifedipine (mean dose, 83 +/- 9 mg/d) was used to decrease blood pressure to less than 140/90 mm Hg. All patients also received furosemide concomitantly for blood pressure control.

RESULTS

Blood pressure reduction with once-daily diltiazem decreased urine albumin excretion (2967 +/- 784 mg/d at baseline compared with 1294 +/- 679 mg/d after diltiazem therapy; P < 0.05) at 4 weeks while patients received a diet consisting of 50 mEq of sodium per day. Albumin excretion did not decrease when sodium intake was increased to 250 mEq/d, and blood pressure was reduced to levels similar to those seen with the low-sodium diet. Similar blood pressure reduction with once-daily nifedipine did not significantly alter albumin excretion regardless of sodium intake.

CONCLUSION

Sodium intake affects the albumin-decreasing effects of certain calcium antagonists. Recent studies suggest that antihypertensive medications that reduce albumin excretion and arterial pressure correlate with reduced renal mortality compared with medications that do not have albumin-decreasing effects. Thus, a low-sodium diet should be prescribed to maximize the albumin-decreasing effects of certain calcium antagonists.

Regulation of the renal response to atrial natriuretic peptide by sodium intake in preweaned rats

The neonate conserves sodium avidly, and sodium intake is normally limited to that present in maternal milk. To evaluate the role of atrial natriuretic peptide (ANP) in this adaptation, preweaned rat pups were artificially reared and fed a formula with either normal sodium (25 mEq/L) or high sodium (145 mEq/L) for 7-8 d. To determine whether increased dietary sodium decreases ANP clearance receptor activity, animals were anesthetized, and the plasma ANP concentration (ANPp), urine flow (V), urinary sodium (UNa V), and cGMP excretion (UcGMP V) were measured before and after infusion of ANF(4-23), an ANP clearance receptor inhibitor (C-ANF), at 50 micrograms/kg/ min. Infusion of C-ANF increased ANPp 10-fold in both normal and high sodium groups, but V, UNa V, and UcGMP V increased only in animals receiving the high sodium diet (p < 0.05). Incubation of isolated glomeruli with 0.1 microM ANP increased extracellular cGMP more in high sodium than normal sodium groups (p < 0.05). We conclude that ANP clearance receptors in the neonate are highly activated regardless of sodium intake. Increased dietary sodium increases the renal diuretic and natriuretic response to circulating ANP through enhanced generation of cGMP.

Effects of chorda tympani transection on long-term salt preference in hamsters

The effects of denervation of fungiform taste buds on preference behavior were studied. Presurgery, 0.01, 0.1, 0.2, and 0.4 M NaCl, and 0.1, 0.2, and 0.4 M KCl were strongly avoided relative to water as measured with 48-h intakes. Bilateral cuts of the chorda tympani nerve (CT) resulted in a decrease in the strength of aversions to all concentrations of NaCl and to 0.2 and 0.4 M KCl. Only 0.4 M NaCl and KCl were strongly avoided after CT section. After CT section, when the animals were allowed to choose between equimolar (0.1 or 0.2 M) KCl and NaCl, they drank equal amounts, whereas intact hamsters preferred KCl to NaCl. In golden hamsters, unlike most laboratory rat strains, intake-based long-term preference behavior for salts is significantly affected by selective gustatory deafferentation.

Postingestive inhibitory controls of independent ingestion in 12-day-old rats

The postingestive inhibitory control of independent ingestion produced by gastric preloads was investigated in 12-day-old Sprague-Dawley rats. Pups received isovolumetric (5% of body weight) preloads of saline (0.9%), glucose (5%, 10%, or 20%) or maltose (5%, 10%, or 20%) 5 min before a 30-min independent ingestion test in which pups licked milk from the floor of the test chamber. All preloads reduced intake significantly compared to the control condition in which pups were intubated, but no preload was administered. The reduction of intake produced by the isovolumetric, isotonic solutions (saline, 5% glucose, and 10% maltose) is consistent with the stimulation of a preabsorptive, inhibitory mechanism sensitive to volume. The significantly larger reduction of intake produced by isovolumetric, hypertonic solutions (20% glucose and 20% maltose) is consistent with the stimulation of an additional postingestive inhibitory mechanism sensitive to the osmotic, saccharidic, or, in the case of 20% glucose, metabolic properties of these solutions. Because preloads were given 5 min prior to the intake tests, it is likely that the site of action of both inhibitory mechanisms was preabsorptive, although a postabsorptive site for part of the inhibitory effect of 20% glucose cannot be excluded.

Urodilatin secretion in salt-loaded Wistar rats

The aim of our study was to investigate whether urodilation (URO, INN: ularitide) is present in rat urine and if URO excretion in the rat is influenced by dietary sodium intake. Therefore, three groups of Wistar rats were placed in metabolic cages where they received different sodium diets for 9 days (0.05%, 0.4%, and 8.0% NaCl, respectively). Food and water intake were determined by weight. At days -4, 2, 5, and 8 blood pressure was measured non invasively using the tail cuff method. After nine days rats were anesthetized and blood was drawn for serum electrolyte, plasma A-type natriuretic peptide (CDD/ANP-99-126), and plasma aldosterone concentration measurements. Using a highly specific antibody against URO combined with high performance liquid chromatography and gel chromatography, we were able to show that a URO-like substance of approx. 3.5 kD that is distinct from CDD/ANP-99-126, brain natriuretic peptide, and C-type natriuretic peptide, is present in rat urine. Sodium chloride loaded rats showed significantly increased urinary excretion rates of URO (p < 0.001), chloride (p < 0.001), sodium (p < 0.001), and the fractional excretion of sodium (p < 0.001). In the plasma, sodium (p < 0.01) and chloride (p < 0.001) increased, while potassium, hematocrit, osmolality, plasma CDD/ANP-99-126, as well as glomerular filtration rate (GFR), and systolic blood pressure did not change. Since CDD/ANP-99-126 is believed to be a natriuretic peptide, it is suggested that CDD/ANP-99-126 might participate in the natriuresis due to high dietary sodium intake. In sodium-loaded rats, however, plasma CDD/ANP-99-126 remains unchanged, while URO excretion increases with sodium excretion, independent of GFR and blood pressure. We conclude that URO secretion is stimulated by dietary salt loading and might be involved in the regulation of water and electrolyte metabolism in the rat.

Renal cytochrome P4504A activity and salt sensitivity in spontaneously hypertensive rats

Differences in the renal metabolism of arachidonic acid by cytochrome P450 have been reported in the spontaneously hypertensive rat (SHR) and Wistar-Kyoto rats, but the contribution of this system to the development of hypertension is unclear. The present study compared renal P450 activity and blood pressure in SHR and Brown-Norway rats (BN) under control conditions and in response to an elevation in sodium intake; genetic linkage analysis was performed in an F2 population (n=219) derived from these strains. Basal renal P4504A enzyme activity measured by conversion of [C(14)]arachidonic acid to 20-hydroxyeicosatetraenoic acid (20-HETE) was significantly greater in the kidneys of adult SHR (n=7) than of BN (n=8) (82 +/- 7 versus 60 +/- 5 pmol/min per milligram protein). Renal 20-HETE production fell 45 percent in SHR and 22 percent in BN in which salt intake was elevated by drinking of saline instead of water for 2 weeks. Mean arterial pressure averaged 157 +/- 3mm Hg in SHR (n = 9) and 100 +/- 2 mm Hg in BN fed a normal salt diet, and it rose to 170 +/- 7 mm Hg (P<.05) in SHR and fell to 90 +/- 3 mm Hg (P<.05) in BN (n=8) after sodium intake was elevated. A polymorphic marker, D5Rjr1, that spanned a repeated element in the P4504A gene on chromosome 5, where all three P4504A isoforms are located, was used for genotyping of the F2 population. The P4504A genotype did not cosegregate with baseline mean arterial pressure in the F2 population; however, significant linkage was observed with the change in mean arterial pressure after sodium intake of the rats was elevated. The degree of linkage differed in male and female rats, and the highest LOD score (3.6) was observed in male F2 rats with a BN grandfather. These findings suggest that the difference in renal P450 activity in SHR and BN does not contribute to the development of hypertension in this F2 population, but it may play some role in determining the blood pressure response to an elevation in salt intake.

TGF and nitric oxide: effects of salt intake and salt-sensitive hypertension

The tubuloglomerular feedback response (TGF) entails vasoconstriction of the afferent arteriole (AA) and a fall in the glomerular capillary pressure (PGC) and single nephron glomerular filtration rate (SNGFR) during NaCl reabsorption in the macula densa (MD) segment. Recent studies have concluded that nitric oxide (NO) is synthesized by the MD and blunts the TGF response. Since a high salt (HS) diet has been found to blunt TGF, we tested the effects of salt intake on the response to blockade of nitric oxide synthesis. For the first series, the TGF was assessed from changes in proximal stop-flow pressure (PSF, an index of PGC in response to graded perfusion of the loop of Henle (LH) with name tubular fluid (NTF). Loop perfusion with 10(-3) M L-NMA did not affect the PSF responses of low salt (LS) rats, but reduced (P < 0.01) the PSF of HS rats during perfusion at 20 nl.min-1 (-1.5 +/- 0.4 mm Hg; P < 0.01) and at 40 nl.ml-1 (-2.2 +/- 0.5 mm Hg; P < 0.001). For the second series, the TGF responses of salt sensitive Dahl/Rapp (ssDR) rats were compared to Sprague-Dawley (SD) rats. Both groups were studied 8 to 10 days after starting HS or LS diets by loop perfusion of artificial tubular fluid at 40 nl.min-1. Compared to Sprague-Dawley rats, the ssDR had blunted maximal TGF responses during LS (SD, 8.2 +/- 0.3 vs. ssDR, 6.4 +/- 0.3 mm Hg; P < 0.001), but not during HS. During LS intake, addition of L-NMA to ATF perfusing the loop of Henle did not alter the maximal TGF response of either strain. However, during HS intake L-NMA increased the maximal TGF response of SD rats (4.4 +/- 0.4 to 6.7 +/- 0.5 mm Hg; P < 0.001) but did not significantly change the PSF of ssDR rats (5.2 +/- 0.3 to 5.7 +/- 0.5 mm Hg; NS). We conclude that the TGF response is enhanced by blockade of NOS during HS, but not LS intakes; this response to NOS blockade during HS intake is lost in salt sensitive Dahl/Rapp rats.

Regulation of the gene-encoding angiotensin II receptor in vascular tissue

Specific angiotensin (Ang)-dependent mechanisms significantly contribute to vascular development and function, and to the pathophysiology of hypertension. The effects of Ang II are mediated by binding to specific receptors. The focus of most studies has been changes in vascular function and structure in response to Ang II. Relatively little is known regarding the molecular basis of changes in the vascular Ang II receptor. We have recently found that, without altering blood pressure, Ang II infusion at a dose of 25 ng.kg.min-1 decreases expression of the gene-encoding Ang II type 1 (AT1) receptor in both the aorta and resistant arteries. This suggests that exogenous Ang II negatively regulates AT1 mRNA expression in these tissues. Furthermore, hypertension induced by reduced renal mass plus high salt intake upregulates AT1 mRNA expression in the hypertrophied aorta and heart. In this model, the reduction of Ang II formation by captopril without decreasing blood pressure prevents the increase in AT1 mRNA in the aorta but not in the heart. This suggests that the regulation of AT1 gene expression in the heart may be pressure-dependent while there is an Ang II-dependent mechanism operant in the aorta. The precise tissue-specific control mechanisms for AT1 gene expression remain to be defined.

Kidney, salt, and hypertension: how and why

A hypothesis is proposed that the aberrant response of the tubuloglomerular feedback to salt load is the abnormality in the kidney in the genesis of essential hypertension. This thesis is based upon the following facts on the kidney, salt and hypertension. To effectively achieve the primary function of the kidney, that is, to maintain the milieu interieur or the extracellular fluids, the kidney must maintain a high glomerular filtration rate (GFR) and almost a complete tubular reabsorption in the face of limited salt intake or low ECF volume and in the face of changes in systemic blood pressure. Autoregulation of renal blood flow and GFR is therefore critical. In addition to myogenic responses in the resistant afferent artery, the juxtaglomerular apparatus (JGA) plays a crucial role in the autoregulation of renal plasma flow and GFR through tubuloglomerular feedback (TGF). That the JGA and TGF have appeared first in amphibian species in evolution suggests that the transition from aquatic sea life, where salt is always in excess to terrestrial life, required this particular structure and function of the kidney. Salt intake in the natural environments on land is very limited, and chronic excess salt intake is a habit peculiar to humans in recent culture or civilization. Thus, it is hypothesized that through evolution the TGF is primarily set to maintain high GFR in the face of low salt intake. We propose that aberrant TGF responses to salt loading may underlie the genesis of essential hypertension in humans. Indeed, hypertension is not seen in human cultures that ingest a very low salt intake.

The influence of dietary salt level on water consumption, farrowing, and reproductive performance of lactating sows

During two consecutive lactations using a switch-back design, 16 sows received a corn, cassava, barley, and soybean meal diet supplemented with either 8.5 or 1 g/kg of NaCl (.4% Na or .1% Na, respectively). The average daily water consumption during the 4-wk lactation period was greater (P < .01) for the sows fed the high-salt diet than for those fed the low-salt diet (13.9 vs 12.4 L, respectively). Urine production accounted for 27% of the water intake during lactation. This resulted in a difference during the entire lactation period of 42.2 L in water consumption (P = .07) and 11.4 L in urine production (P = .07). The Na and Cl concentrations of the urine for sows fed the high-salt diet were higher than for sows fed the low-salt diet (P < .05), but the K, Mg, P, and Ca concentrations were not influenced. The milk composition, measured at d 1, 13, and 27 of lactation, was relatively independent of the dietary salt level, except for the Cl concentration at d 1 after farrowing, which was higher (P < .05) for sows fed the high-salt diet. The moisture and ash content of the milk increased with the length of the lactation, irrespective of the diet. The increased ash content on d 13 and 27 of lactation was accounted for by the increased concentrations of P and Ca. There was no effect of dietary salt level on weight change of the sow or on the growth performance of the pigs. The interval from weaning to estrus (n = 13, t = 2.48, P = .029) was shorter for sows fed the high-salt diet than for sows fed the low-salt diet (6.2 +/- 1.0 and 12.6 +/- 3.1 d, respectively). More sows were unsuccessfully mated after receiving the low-salt diet during lactation. These results indicate that a low-salt diet for lactating sows results in lower water consumption, lower urine production, and lower Na and Cl concentrations in the urine. Milk composition, weight change of the sow, and growth performance of the pigs were not altered, but reproductive failures afterward may point to a salt deficiency during lactation.

Age-dependent influence on heart rate variability in salt-sensitive hypertensive subjects

OBJECTIVE

The known association between systemic arterial hypertension in its initial stages and increased sympathetic nervous system drive prompted us to evaluate the influence of age on autonomic nervous system function in subjects with salt-sensitive arterial hypertension.

DESIGN

In a randomized study, autonomic nervous system function was assessed by power spectral analysis of heart-rate variability calculated with an autoregressive algorithm in salt-sensitive hypertensives and controls at baseline and under sympathetic stress (passive head-up tilt). For 1 week before the study, all subjects kept to a diet supplying 120 mEq sodium. Sodium sensitivity was assessed by measuring and comparing arterial pressures after a 7-day controlled dietary sodium intake of 20 mEq per day after a 7-day period on 220 mEq sodium/day.

SETTING

Geriatric division at the I Medical Clinic of the University of Rome "La Sapienza".

PARTICIPANTS

Sixty-five patients with salt-sensitive hypertension (age range 19 to 89 years) and 64 age-matched normotensive controls, divided for data comparison into three age-groups: < 44 years; 44 to 64 years; and > or = 65 years.

MEASUREMENTS

With an autoregressive algorithm in a power spectral analysis of heart rate variability, we detected four spectral frequency-domains: total power (0.0033 to 0.40 Hz), high-frequency power (0.16 to 0.40 Hz), low-frequency power (0.04 to 0.15 HZ) and very-low-frequency power (0.0033 to 0.04 Hz). To determine sodium sensitivity, for 1 week before the study all subjects kept to a diet supplying 120 mEq sodium. Sodium sensitivity was assessed by measuring and comparing arterial pressures after a 7-day controlled dietary intake of 20 mEq per day and after a 7-day period of 220 mEq sodium/day.

RESULTS

Results were expressed as natural logarithms of power and normalized units. The hypertensive patients of all ages had significantly lower total power of heart rate variability than the normotensive controls (P < .05). At baseline, the youngest hypertensives had lower natural logarithms and low-frequency normalized units than controls (P < .001). After tilt, only their low-frequency normalized units exceeded those of controls (P < .001). The middle-aged hypertensive group had higher low-frequency normalized units than controls at baseline (P < .05) and after tilt (P < .001). At baseline and after tilt, the oldest hypertensives had lower low-frequency natural logarithms than controls (P < .05) and normalized units equal to those of controls. But the hypertensives of all ages were less able than controls (P < .001) to increase low-frequency power after head-up tilt. In the less than 44-year-old hypertensives, diastolic pressure correlated significantly with low-frequency power of heart rate variability, expressed in normalized units, at baseline (P < .05) and after head-tilt (P < .05). A significant inverse correlation was found between age and the natural logarithm of low-frequency power at baseline (r = -.682, P < .001) and after tilt (r = -.800; P < .001). Also, a significant inverse correlation was found to exist in normotensive subjects between the natural logarithm of low-frequency at baseline (r = -.595; P < .001) and after tilt (r = -.391; P < .001). The two regression line coefficients for age correlated significantly (P < .001) with the natural logarithm of low-power frequency after tilt.

CONCLUSION

Whereas sodium chloride-sensitive hypertension appears to be associated with sympathetic hyperactivity in young and middle-aged subjects, in older people it is not. Sympathetic activity diminishes with age, declining faster in hypertensive subjects.

The subtype-2 (AT2) angiotensin receptor regulates renal cyclic guanosine 3', 5'-monophosphate and AT1 receptor-mediated prostaglandin E2 production in conscious rats

The renal effects of angiotensin II(AII) are attributed to AT1 receptors. In contrast, the function of renal AT2 receptors in unknown. Using a microdialysis technique, we monitored changes in renal interstitial fluid (RIF) prostaglandin E2 (PGE2) and cyclic guanosine 3', 5'-monophosphate (cGMP) in response to dietary sodium (Na) depletion alone, or Na depletion or normal Na diet combined with the AT1 receptor blocker, Losartan, the AT2 receptor blocker, PD 123319 (PD), or angiotensin II, individually or combined in conscious rats. Na depletion significantly increased PGE2 and cGMP. During Na depletion, Losartan decreased PGE2 and did not change cGMP. In contrast, PD significantly increased PGE2 and decreased cGMP. Combined administration of Losartan and PD decreased PGE2 and cGMP. During normal Na diet, RIF PGE2 and cGMP increased in response to angiotensin II. Neither Losartan nor PD, individually or combined, changed RIF PGE2 or cGMP. Combined administration of angiotensin II and Losartan or PD produced a significant decrease in response of PGE2 and cGMP to angiotensin II, respectively. These data demonstrate that activation of the reninangiotensin system during Na depletion increases renal interstitial PGE2 and cGMP. The AT1 receptor mediates renal production of PGE2. The AT2 receptor mediates cGMP. AT2 blockade potentiates angiotensin-induced PGE2 production at the AT1 receptor.

Autoradiographic localization of active renin in the juxtaglomerular apparatus of the dog kidney: effects of sodium intake

1. The effects of dietary sodium intake on active renin binding in the juxtaglomerular apparatus (JGA) of superficial and juxtamedullary cortex of the dog kidney were examined by quantitative in vitro autoradiography using a radiolabelled renin inhibitor [125I]-H77, which has high affinity for dog renin. 2. Changes in sodium intake resulted in marked alterations of active renin binding in the radiolabelled JGA. In comparison with the control kidney (190.8 +/- 7.7 Bq/mm3), a higher density of binding occurred in the labelled JGA of sodium-depleted kidney (277.7 +/- 6.2 Bq/mm3), while a lower density of binding was found in the labelled JGA of sodium-loaded kidney (99.3 +/- 7.4 Bq/mm3). 3. Active renin binding in the labelled JGA was significantly higher in superficial JGA than in their juxtamedullary counterparts, irrespective of sodium intake. 4. Pre-incubation with trypsin (0.5 mg/mL), a procedure known to activate prorenin, markedly increased active renin binding in the labelled JGA of control (+ approximately 35%; P < 0.01) and sodium-loaded kidneys (+ approximately 75%; P < 0.01), but had little effect on binding in the labelled JGA of the sodium-depleted kidney (+/- approximately 5-10%; NS). The proportions of active renin as a percentage of total renin were 60, 75 and 95% in the labelled JGA of sodium-loaded, control, and sodium-depleted kidneys, respectively. 5. Emulsion microscopic autoradiography revealed that the binding was exclusively localized in the JGA, including the afferent and efferent arterioles, macula densa and extraglomerular mesangium. Labelling extended to the interlobular arteries in sodium depleted kidney. 6. These results indicate that autoradiography combined with the in vitro binding of radiolabelled renin inhibitors may provide a useful tool to measure active and prorenin renin and thereby study the physiological regulation of renin in the kidney.

Changes in secreted salivary sodium are sufficient to alter salt taste sensitivity: use of signal detection measures with continuous monitoring of the oral environment

A signal detection measure of NaCl taste sensitivity was developed with continuous monitoring of the Na+ concentration of the oral environment. Taste sensitivity was reduced when saliva was stimulated by chewing to secrete with elevated Na+ levels. Monitoring of the oral environment for Na+ allowed a computation of physical signal strengths for NaCl and water stimuli; changes in these strengths, brought about by variations in secreted salivary sodium, furnish an explanation for alterations in NaCl taste sensitivity.

Dietary sodium intake and cardiac nerve cell hypertrophy in Wistar rats

We determined the effect of dietary sodium intake (0.15 and 8% NaCl) on the cardiac neuron size of normotensive 3-week old Wistar rats. An increase in dietary sodium for 48 weeks induced an increase in neuronal size. The number of large neurons (larger than 500 microns 2) increased significantly (chi-square test) in rats ingesting 8% NaCl in their food. The rats presented hypertension (128 +/- 9 vs 134 +/- 16 mmHg; difference not significant, Student t-test) and a statistically significant increase in cardiac muscle mass (1.6 +/- 0.1 vs 2.0 +/- 0.2 mg/g of rat). We conclude that food sodium can significantly increase cardiac nerve cell size and this trophic response occurs concomitantly with an increase of cardiac muscle mass.

Dietary cholesterol enhances impaired endothelium-dependent relaxations in aortas of salt-induced hypertensive Dahl rats

We investigated the effect of hypercholesterolemia on the vascular reactivity of thoracic aortas isolated from hypertensive Dahl salt-sensitive (DS) rats. DS rats were fed on a low-sodium diet (control group), a low-sodium plus high-cholesterol diet (CHOL group), a high-sodium diet (NaCl group) or a high-sodium plus high-cholesterol diet (NaCl + CHOL group) for 8 weeks. Hypercholesterolemia developed in the CHOL and NaCl + CHOL groups, while hypertension developed in the NaCl and NaCl + CHOL groups, with these changes being greatest in the NaCl + CHOL group. Aortic cholesteryl ester accumulation was attenuated in the aortic rings from the NaCl and NaCl + CHOL groups, compared to the control group. The degree of attenuation in the NaCl + CHOL group was significantly greater than that in the NaCl group. Endothelium-dependent relaxations induced by the calcium ionophore A23187 were attenuated only in the NaCl + CHOL group. Endothelium-independent relaxations in response to sodium nitroprusside were slightly but significantly attenuated in the NaCl + CHOL group. The relaxations in the CHOL group were comparable to those in the control group. These findings indicate that cholesterol feeding strikingly enhances the impaired endothelium-dependent relaxations and the slightly impaired endothelium-independent relaxations in the aorta of DS rats with salt-induced hypertension, parallel to the development of hypertension, hypercholesterolemia and cholesterol deposition.

Breakdown of blood pressure and body fluid homeostasis in heart transplant recipients

OBJECTIVES

This study was designed to investigate disturbances in arterial blood pressure and body fluid homeostasis in stable heart transplant recipients.

BACKGROUND

Hypertension and fluid retention frequently complicate heart transplantation.

METHODS

Blood pressure, renal and endocrine responses to acute volume expansion were compared in 10 heart transplant recipients (57 +/- 9 years old [mean +/- SD]) 20 +/- 5 months after transplantation, 6 liver transplant recipients receiving similar doses of cyclosporine (cyclosporine control group) and 7 normal volunteers (normal control subjects). After 3 days of a constant diet containing 87 mEq/24 h of sodium, 0.154 mol/liter saline was infused at 8 ml/kg per h for 4 h. Blood pressure and plasma vasopressin, angiotensin II, aldosterone, atrial natiuretic peptide and renin activity levels were determined before and at 30, 60, 120 and 240 min during the infusion. Urine was collected at 2 and 4 h. Blood pressure, fluid balance hormones and renal function were monitored for 48 h after the infusion.

RESULTS

Blood pressure did not change in the two control groups but increased in the heart transplant recipients (+15 +/- 8/8 +/- 5 mm Hg) and remained elevated for 48 h (p < or = 0.05). Urine flow and urinary sodium excretion increased abruptly in the control groups sufficient to account for elimination of 86 +/- 9% of the sodium load by 48 h; the increases were blunted (p < or = 0.05) and delayed in the heart transplant recipients, resulting in elimination of only 51 +/- 13% of the sodium load. Saline infusion suppressed vasopressin, renin activity, angiotensin II and aldosterone in the two control groups (p < or = 0.05) but not in the heart transplant recipients. Heart transplant recipients had elevated atrial natriuretic peptide levels at baseline (p < or = 0.05), but relative increases during the infusion were similar to those in both control groups.

CONCLUSIONS

Blood pressure in heart transplant recipients is salt sensitive. These patients have a blunted diuretic and natriuretic response to volume expansion that may be mediated by a failure to reflexly suppress fluid regulatory hormones. These defects in blood pressure and fluid homeostasis were not seen in liver transplant recipients receiving cyclosporine and therefore cannot be attributed to cyclosporine alone. Abnormal cardiorenal neuroendocrine reflexes, secondary to cardiac denervation, may contribute to salt-sensitive hypertension and fluid retention in heart transplant recipients.

Does the renin-angiotensin system determine the renal and systemic hemodynamic response to sodium in patients with essential hypertension?

Many patients with essential hypertension respond to a high dietary sodium intake with a rise in blood pressure. Experimental evidence suggests that the renal hemodynamic response to sodium determines, at least partially, this rise in blood pressure. Our aim was to clarify the role of the renin-angiotensin system in the renal and systemic adaptation to a change in dietary sodium. We studied changes in mean arterial pressure (MAP) (millimeters of mercury), effective renal plasma flow (ERPF), body weight, and immunoreactive renin in 17 patients with essential hypertension and 15 normotensive control subjects, randomly crossing over between a 3-week sodium-restricted (50 mmol/24 h) and a sodium-replete (200 mmol/24 h) diet period. In addition, the effects of renin inhibition by remikiren (600 mg, single oral dose) were studied during the high sodium period. In normotensive control subjects, high sodium intake had no effect on MAP or body weight, whereas ERPF increased (490 +/- 19 to 535 +/- 21 mL/min, P < .05) and immunoreactive renin decreased (32 +/- 6 to 14 +/- 1 pg/mL). In hypertensive subjects, high sodium intake induced a heterogeneous response of MAP (median change, 2.6 mm Hg; range, -4.7 to +21.2; P = NS) and ERPF (median change, 21 mL/min; range, -33 to +98; P = NS). Body weight increased from 81.3 +/- 1.9 to 82.5 +/- 2.0 kg (P < .05), and immunoreactive renin decreased from 18 +/- 3 to 10 +/- 1 pg/mL (P < .05). Interestingly, the patients with a distinct rise in MAP showed a blunted ERPF response to high sodium intake (r = -.70, P < .01) and an increase in body weight (r = .76, P < .001). Moreover, the increase of ERPF was more pronounced in patients with a larger fall in immunoreactive renin (r = .77, P < .001). After administration of remikiren, a heterogeneous response in ERPF was observed: the patients with the blunted ERPF response to high sodium intake showed the largest ERPF rise (r = .70, P < .01). The remikiren-induced rise in ERPF correlated (r = .68, P < .01) with the fall in MAP (114 +/- 2 to 110 +/- 2 mm Hg). In conclusion, in patients with essential hypertension a rise in blood pressure in response to high sodium intake appears to partially be the result of insufficient renal vasodilatation. This seems to be due to an inadequate (intrarenal?) renin-angiotensin system response to increased sodium intake.

Effects of dietary sodium on blood pressure in IDDM patients with nephropathy

The objectives of the study were to assess the effects of moderate sodium restriction on blood pressure in insulin-dependent diabetic (IDDM) patients with nephropathy and high normal or mildly hypertensive blood pressure (primary objective), and to document possible associated changes of exchangeable body sodium, body volumes, components of the renin-angiotensin-aldosterone system, atrial natriuretic peptide, and catecholamines (secondary objective). Sixteen patients with untreated systolic blood pressure > or = 140 < 160 mmHg and/or diastolic blood pressure > or = 85 < 100 mmHg were included in a double-blind, randomized, placebo-controlled trial. After a 4-week run-in period on their usual diet and a 2-week dietary training period to reduce sodium intake to about 90 mmol/day, eight patients received 100 mmol/day sodium supplement (group 2) and eight patients a matching placebo (group 1) for 4 weeks while continuing on the reduced-sodium diet. Patients were examined at weekly intervals. Main response variables were mean values of supine and sitting systolic and diastolic blood pressure as measured in the clinic and by the patients at home. The differences in blood pressure between the beginning and the end of the blinded 4-week study period were calculated and the differences in changes between the two patient groups were regarded as the main outcome parameters. During the blinded 4-week study period, average urinary sodium excretion was 92 +/- 33 (mean +/- SD) mmol/day in group 1 and 199 +/- 52 mmol/day in group 2 (p = 0.0002). The differences in blood pressure changes between the two patient groups were 3.9(-1.2 to 9) mmHg [mean (95% confidence intervals)] for systolic home blood pressure, 0.9(-3.7 to 5.5) mmHg for diastolic home blood pressure, 4.9(-3.3 to 13.1) mmHg for clinic systolic blood pressure and 5.3(1 to 9.7 mmHg, p = 0.02) for clinic diastolic blood pressure. Combining all patients, there were relevant associations between changes of urinary sodium excretion and blood volume (Spearman correlation coefficient r = 0.57), blood pressure and angiotensin II (diastolic: r = -0.7; systolic: r = -0.48), and exchangeable body sodium and renin activity (r = -0.5). In conclusion, in this study of IDDM patients with nephropathy and high normal or mildly hypertensive blood pressure, a difference in sodium intake of about 100 mmol/day for a period of 4 weeks led to a slight reduction of clinic diastolic blood pressure. Studies including larger numbers of patients with various stages of nephropathy and hypertension are needed to definitely clarify the effects of sodium restriction in IDDM.

Increased prevalence of salt sensitivity of blood pressure in IDDM with and without microalbuminuria

In insulin-dependent diabetes mellitus (IDDM) elevated exchangeable sodium (Na) levels are found even in the absence of hypertension, but it is not known whether this is associated with increased sensitivity of blood pressure to sodium level. To clarify this issue we compared 30 patients with IDDM (19 without and 11 with microalbuminuria, i.e. more than 30 mg albumin/day) and 30 control subjects matched for age, gender and body mass index. The subjects were studied on the 4th day of a low-salt diet (20 mmol/day) under in-patient conditions and were subsequently changed to the same diet with a high-salt supplement, yielding a total daily intake of 220 mmol Na/day. Circadian blood pressure, plasma renin activity (PRA), plasma atrial natriuretic factor (p-ANF), plasma cyclic guanosine 5'-phosphate (p-cGMP) and urinary albumin were measured. The proportion of salt-sensitive subjects, i.e. showing increment of mean arterial pressure > or = 3 mmHg on high-salt diet, was 43% in diabetic patients (50% of diabetic patients with and 37% without microalbuminuria) and 17% in control subjects (p < 0.05). Lying and standing PRA levels on low- or high-salt diet were significantly lower in diabetic patients than in control subjects. Salt-sensitive diabetic patients had significantly higher lying ANF on high-salt (38.7 +/- 4.2 pmol/l vs 20.1 +/- 2.3 pmol/l, p < 0.005) than on low-salt diet. The results suggest that (i) the prevalence of sodium sensitivity is high in IDDM (ii) sodium sensitivity is found even in the absence of nephropathy as indicated by albuminuria.

[Association of plasma insulin with blood pressure and sodium sensitivity in children]

To study the relationship between plasma insulin level, sodium sensitivity and blood pressure, 150 children aged from 10 to 15 years with high blood pressure and 150 children matched for age and sex but with normal blood pressure were measured for plasma insulin with radioimmunoassay and sodium sensitivity with the tests of oral saline load and furosemide sodium-volume depletion and followed for 5 years. The results showed that (1) In children with HBP and positive family history of hypertension (FH+), the plasma insulin level was significantly higher than that in the respective control group (P < 0.01); (2) In children with high plasma insulin level, the percentiles of systolic blood pressure kept high and had a rising tendency during the follow-up period; (3) In children with sodium sensitivity, the plasma insulin level was higher than that in children with sodium resistance (P < 0.01) and the plasma insulin level correlated positively with blood pressure increasing rate of post-load (P < 0.05). It is suggested that insulin resistance was associated with sodium sensitivity, and they might play a role in the development of hypertension in childhood.

Salt and left ventricular hypertrophy: what are the links?

Left ventricular hypertrophy is a frequent and prognostically unfavourable finding in patients with essential hypertension and has been found to be a predictor for the development of essential hypertension in normotensive subjects. Among various genetic, haemodynamic and humoral determinants, dietary salt intake has been demonstrated to influence left ventricular mass in hypertensive disease. Several cross-sectional studies have shown a close relation between dietary salt intake and parameters of left ventricular hypertrophy. Moreover, reduction of dietary sodium intake was associated with a decrease of left ventricular mass in a prospective study. The underlying mechanism of how salt intake modulates myocardial structure has not been explained yet. Three possible explanations are discussed: (1) sodium influences left ventricular mass via raised preload, (2) the sympathetic nervous system acts as a mediator, and (3) the renin-angiotensin-aldosterone system is the responsible link. Recent animal experiments and clinical studies suggest that the renin-angiotensin-aldosterone system may mediate both the cardiotrophic and the blood pressure raising effects of salt. However, not all individuals have a similar high susceptibility to blood pressure elevation develop left ventricular hypertrophy when exposed to high salt intake. We suggest that the underlying mechanism is a dysregulation of the renin-angiotensin-aldosterone system. Some individuals may have an impaired downregulation of angiotensin II synthesis when challenged with high salt intake. Accordingly, we found that relatively too high levels of angiotensin II in relation to urinary sodium excretion were associated with left ventricular hypertrophy in these individuals on high salt intake.

Dietary sodium intake modulates systemic but not forearm norepinephrine release

INTRODUCTION

Sodium intake has profound effects on systemic and renal sympathetic activity, but its effects on sympathetic activity in skeletal muscle vascular beds, a site at which local regulatory mechanisms could alter vascular tone directly, are unclear.

METHODS

To determine the effect of dietary sodium intake on basal and isoproterenol-stimulated systemic and forearm norepinephrine kinetics, we studied seven healthy male volunteers twice, 4 weeks apart, while they were receiving a low-sodium (10 mmol sodium/24 hours) diet and a high-sodium diet (250 mmol sodium/24 hours). Forearm blood flow, measured by plethysmography, and systemic and forearm norepinephrine spillover, measured by radioisotope dilution, were determined before and after intra-arterial infusion of 60 and 400 ng/min isoproterenol.

RESULTS

Baseline (before isoproterenol) systemic norepinephrine spillover was higher when subjects received the low-sodium diet (448.1 +/- 55.7 ng/min) compared with the high-sodium diet (269.7 +/- 42.7 ng/min; p < 0.05). In contrast, sodium intake did not affect local forearm norepinephrine spillover, either at baseline (low-sodium diet, 2.05 +/- 0.48 ng/min versus high-sodium diet, 2.63 +/- 0.79 ng/min; p = 0.50) or after stimulation with isoproterenol in doses of 60 ng/min (low-sodium diet, 8.84 +/- 2.2 ng/min versus high-sodium diet, 6.1 +/- 1.9 ng/min; p = 0.38) or 400 ng/min (low-sodium diet, 16.4 +/- 4.5 ng/min versus high-sodium diet, 16.7 +/- 2.5 ng/min; p = 0.93).

CONCLUSIONS

Under conditions of low sodium intake, systemic norepinephrine spillover was increased but forearm norepinephrine spillover was not, suggesting that alteration in sodium intake may produce a differential effect on norepinephrine spillover in different tissues but that decreased local sympathetic activity in skeletal muscle is not the likely mechanism by which a low-sodium diet may lower blood pressure or attenuate stress-induced pressor responses.