Determination of trace lithium in biological fluids using graphite furnace atomic absorption spectrophotometry: variability of urine matrices circumvented by cation exchange solid phase extraction

Twenty-Four Hour Blood Pressure Response to Empagliflozin and Its Determinants in Normotensive Non-diabetic Subjects

Background

Sodium–glucose co-transport 2 inhibitors (SGLT2i) lower blood pressure (BP) in normotensive subjects and in hypertensive and normotensive diabetic and non-diabetic patients. However, the mechanisms of these BP changes are not fully understood. Therefore, we examined the clinical and biochemical determinants of the BP response to empagliflozin based on 24-h ambulatory BP monitoring.

Methods

In this post-hoc analysis of a double-blind, randomized, placebo-controlled study examining the renal effects of empagliflozin 10 mg vs. placebo in untreated normotensive non-diabetic subjects, the 1-month changes in 24 h ambulatory BP were analyzed in 39 subjects (13 placebo/26 empagliflozin) in regard to changes in biochemical and hormonal parameters.

Results

At 1 month, empagliflozin 10 mg decreased 24-h systolic (SBP) and diastolic (DBP) BP significantly by −5 ± 7 mmHg (p < 0.001) and −2 ± 6 mmHg (p = 0.03). The effect on SBP and DBP was more pronounced during nighttime (resp. −6 ± 11 mmHg, p = 0.004; −4 ± 7 mmHg, p = 0.007). The main determinants of daytime and nighttime SBP and DBP responses were baseline BP levels (for daytime SBP: coefficient −0.5; adj. R²: 0.36; p = 0.0007; for night-time SBP: coefficient −0.6; adj. R²: 0.33; p = 0.001). Although empaglifozin induced significant biochemical changes, none correlated with blood pressure changes including urinary sodium, lithium, glucose and urate excretion and free water clearance. Plasma renin activity and plasma aldosterone levels increased significantly at 1 month suggesting plasma volume contraction, while plasma metanephrine and copeptin levels remained the same. Renal resistive indexes did not change with empagliflozin.

Conclusion

SGLT2 inhibition lowers daytime and nighttime ambulatory systolic and diastolic BP in normotensive non-diabetic subjects. Twenty-four jour changes are pronounced and comparable to those described in diabetic or hypertensive subjects. Baseline ambulatory BP was the only identified determinant of systolic and diastolic BP response. This suggests that still other factors than sustained glycosuria or proximal sodium excretion may contribute to the resetting to lower blood pressure levels with SGLT2 inhibition.

Clinical Trial Registration:

[https://www.clinicaltrials.gov], identifier [NCT03093103].

No renal dysfunction or salt and water retention in acute mountain sickness at 4,559 m among young resting males after passive ascent

This study examined the role and function of the kidney at high altitude in relation to fluid balance and the development of acute mountain sickness (AMS), avoiding confounders that have contributed to conflicting results in previous studies. We examined 18 healthy male resting volunteers (18-40 yr) not acclimatized to high altitude while on a controlled diet for 24 h at Lausanne (altitude: 560 m) followed by a period of 44 h after reaching the Regina Margherita hut (4,559 m) by helicopter. AMS scores peaked after 20 h at 4,559 m. AMS was defined as functional Lake Louise score ≥ 2. There were no significant differences between 10 subjects with and 8 subjects without AMS for urinary flow, fluid balance, and weight change. Sodium excretion rate was lower in those with AMS after 24 h at altitude. Microalbuminuria increased at altitude but was not different between the groups. Creatinine clearance was not affected by altitude or AMS, whereas clearances of sinistrin and p-aminohippuric acid decreased slightly, somewhat more in those without AMS. Plasma concentrations of epinephrine, norepinephrine, atrial natriuretic factor, and vasopressin increased whereas renin activity, angiotensin, and aldosterone decreased at altitude. Circulating hormone concentrations did not differ between those with and without AMS. Summarizing, in healthy resting young men flown by helicopter to 4,559 m, renal function was not affected by hypoxia except for minor microalbuminuria, high altitude diuresis did not occur, and AMS was not associated with salt and water retention or renal dysfunction.NEW & NOTEWORTHY Kidney function remained essentially unaffected and acute mountain sickness (AMS) was not associated with salt and water retention in healthy young men flown to and resting at the Margherita hut (4,559 m) under strictly controlled conditions maintaining water, salt, and food intake at pre-exposure levels. Thus, renal dysfunction and fluid retention are not essential factors contributing to the pathophysiology of AMS.

Impact of obesity with or without hypertension on systemic haemodynamic and renal responses to lower body negative pressure

PURPOSE

Sodium and water handling by the kidney and the sympathetic nervous system have been implicated in the development of obesity-related hypertension and kidney disease. They have seldom been studied together during stress conditions. The objective of this study was to compare the systemic, renal and hormonal responses to lower body negative pressure (LBNP) in adult healthy participants (H), obese normotensive (OBN) and obese hypertensive patients (OBH).

MATERIALS AND METHODS

This was a prospective case-control study. Participants from the three groups were exposed to one hour of LBNP. Systemic and renal haemodynamics, sodium and water excretion and hormones were measured before and after LBNP. Intergroup LBNP responses were tested using a Student t-test or a Wilcoxon rank-sum test. An extension of the Wilcoxon rank-sum test was used to test for a trend across the three groups.

RESULTS

The study included 54 participants (H: 25, OBN: 16, OBH: 13). LBNP induced a stepwise increase in systolic blood pressure (+2.7 ± 4.7 mmHg (H) vs. +4.7 ± 8.8 mmHg (OBN) vs. +8.0 ± 8.6 mmHg (OBH, p = .028)) and heart rate (-1.3 ± 4.9 bpm (H) vs. 2.2 ± 6.1 bpm (OBN) vs. 1.9 ± 4.1 bpm (OBH, p = .041). Urinary output (-2.8 ± 2.1 ml/min vs. -1.4 ± 1.7 ml/min, p = .028) and free water clearance (-1.9 ± 1.7 mOsm/kg vs. -0.7 ± 1.3 mOsm/kg, p = .016) responses were more marked in OBN compared to H.

CONCLUSIONS

These results show that the systemic and the renal response to LBNP differ according to weight and to BP categories. Systolic BP and heart show a progressive increased response form healthy volunteers to OBN and then to obese hypertensive participants while urinary output and free water clearance responses are increased in OBN only, suggesting that the occurrence of hypertension in obese individuals modifies the early kidney responses to stress.

CLINICALTRIAL.GOV IDENTIFIER

NCT01734096.

Blood Pressure and Renal Responses to Orthostatic Stress Before and After Radiofrequency Renal Denervation in Patients with Resistant Hypertension

Background/Aims

In patients with resistant hypertension, renal denervation (RDN) studies have mainly focused their outcomes on blood pressure (BP). The aim of this study was to evaluate the long-term effect of RDN on neurohormonal profiles, renal hemodynamics and sodium excretion in a resting state and during stress induced by lower body negative pressure (LBNP).

Materials and methods

This was a single center prospective observational study. Norepinephrine, plasma renin activity (PRA), glomerular filtration rate (GFR), renal plasma flow (RPF) and sodium excretion were measured in unstimulated conditions (rest) and after one hour of LBNP at three different time points: before (M0), one (M1) and twelve months (M12) after RDN.

Results

Thirteen patients with resistant hypertension were included. In the resting state, no differences were observed in norepinephrine, PRA, sodium excretion and mean BP levels after RDN. GFR (78 ± 32 ml/min at M0 vs 66 ± 26 ml/min at M12 (p = 0.012) and filtration fraction (22.6 ±5.4% at M0 vs 15.1 ±5.3% at M12 (p = 0.002)) both decreased after RDN. During LBNP, the magnitude of the mean BP increase was reduced from +6.8 ± 6.6 mm Hg at M0 to +2.3 ± 1.3 mm Hg at M12 (p = 0.005). The LBNP-induced increase in norepinephrine and decrease in GFR and sodium excretion observed before RDN were blunted after the procedure.

Conclusion

A decrease in GFR and filtration fraction was observed one year after RDN. In addition, our results suggest that RDN blunts not only the norepinephrine but also the mean BP, the GFR and the sodium excretion responses to an orthostatic stress one year after the intervention.

Registry number

NCT01734096

Hemodynamic effect of angiotensin II receptor blockade in postmenopausal women on a high-sodium diet: A double-blind, randomized, placebo-controlled study

BACKGROUND

Hypertension becomes increasingly prevalent after menopause. Postmenopausal women are more responsive to salt than premenopausal women, and they have been reported to develop marked renal vasoconstriction on a high-sodium diet.

OBJECTIVE

The aim of this study was to assess whether angiotensin II receptor blockade can restore a normal pattern of renal response to salt in postmenopausal women on a high-sodium diet. We also assessed segmental renal sodium handling in that population.

METHODS

Normotensive and hypertensive postmenopausal women not receiving hormone replacement therapy were enrolled in this prospective, double-blind, placebo-controlled, crossover study. They were assigned to receive irbesartan 150 mg or placebo for 6 weeks; the sequence in which they received irbesartan or placebo was randomized. During the last week of treatment, they received a high-sodium diet (250 mmol/d). Ambulatory blood pressure (ABP), glomerular filtration rate (GFR), and effective renal plasma flow (ERPF) were measured using sinistrin and para-amino-hippurate clearances. Renal sodium handling was assessed by measuring endogenous lithium clearance on day 7 of the high-salt diet.

RESULTS

Nineteen women (mean age, 54.7 years; range, 43-72 years; 7 normotensive subjects [mean age, 53.4 years; range, 47-61 years] and 12 hypertensive subjects [mean age, 55.4 years; range, 43-72 years]) were included in the study. When the data for all 19 subjects were pooled, ABP was significantly lower with irbesartan than placebo both during the day (120 [3]/79 [2] vs 127 [3]/85 [2] mm Hg; both, P < 0.01) and at night (systolic BP, 107 [4] vs 111 [4] mm Hg [P < 0.01] and diastolic BP, 71 [2] vs 75 [2] mm Hg [P < 0.05]). Compared with placebo, irbesartan was not associated with a significant change in GFR in either the normotensive or the hypertensive women. When the data for all 19 subjects were pooled, irbesartan was associated with a significant increase in ERPF compared with placebo (372 [21] vs324 [18] mL/min · 1.73 m(2); P < 0.05). When the hypertensive and normotensive women were considered separately, the effect was more pronounced in the hypertensive women than in the normotensive women, but the changes did not reach statistical significance. When the data for all subjects were pooled, irbesartan was associated with a significant increase in daytime urinary sodium excretion compared with placebo (135 [13] vs 106 [13] μmol/min; P < 0.05) and a significant decrease at night (109 [13] vs 136 [19] μmol/min; P < 0.05). Fractional excretion of lithium (FELi), an inverse marker of proximal sodium reabsorption, increased significantly during the daytime with irbesartan compared with placebo (47% [6.5%] vs 35% [4.7%]; P < 0.05). At nighttime, FELi was significantly higher in the hypertensive subjects receiving irbesartan compared with placebo (43% [7.2%] vs 29% [6.5%]; P < 0.05). The fractional distal reabsorption of sodium did not change significantly with irbesartan compared with placebo.

CONCLUSIONS

The results from this study suggest that angiotensin II receptor blockade had a favorable impact on BP, renal hemodynamics, and renal sodium handling in these salt-replete postmenopausal women. Blockade of the renin-angiotensin system restored the normal pattern of renal response to high sodium intake in these women.

Blood pressure in relation to interactions between sodium dietary intake and renal handling

There is abundant evidence that sodium intake is related to blood pressure. However, the relationship varies between individuals and is probably determined by renal sodium handling. We investigated clinic and ambulatory blood pressure in relation to interactions between sodium dietary intake and renal handling, as assessed by 24-hour urinary sodium excretion and endogenous lithium clearance, respectively. We calculated fractional excretion of lithium and fractional distal reabsorption rate of sodium, as markers of proximal and distal sodium handling, respectively. The 766 subjects included 379 men and 478 ambulatory hypertensive patients. They were never treated (n=697) or did not take antihypertensive medication for ≥2 weeks (n=69). In adjusted analyses, none of the associations of urinary sodium excretion, fractional excretion of lithium, and fractional distal reabsorption rate of sodium with clinic or ambulatory blood pressure were statistically significant (P≥0.09). However, there was significant (P=0.01) interaction between urinary sodium excretion and fractional excretion of lithium in relation to nighttime diastolic blood pressure. In tertile 3 but not tertiles 1 and 2 of fractional excretion of lithium, nighttime diastolic pressure was positively associated with urinary sodium excretion (P=0.03). However, nighttime diastolic pressure was higher in tertile 1 than tertile 3 of fractional excretion of lithium (+2.0 mm Hg; P=0.01), especially in the bottom tertile of urinary sodium excretion (+4.9 mm Hg; P<0.001). Similar trends were observed for nighttime systolic pressure and clinic and 24-hour diastolic pressure. In conclusion, sodium dietary intake and proximal tubular handling interact to be associated with blood pressure.

Effects of the peroxisome proliferator-activated receptor (PPAR)-gamma agonist pioglitazone on renal and hormonal responses to salt in diabetic and hypertensive individuals

AIMS/HYPOTHESIS

Glitazones are powerful insulin sensitisers prescribed for the treatment of type 2 diabetes. Their use is, however, associated with fluid retention and an increased risk of congestive heart failure. We previously demonstrated that pioglitazone increases proximal sodium reabsorption in healthy volunteers. This study examines the effects of pioglitazone on renal sodium handling in individuals prone to insulin resistance, i.e. those with diabetes and/or hypertension.

METHODS

In this double-blind randomised placebo-controlled four-way crossover study, we examined the effects of pioglitazone (45 mg daily during 6 weeks) or placebo on renal, systemic and hormonal responses to changes in sodium intake in 16 individuals, eight with type 2 diabetes and eight with hypertension.

RESULTS

Pioglitazone was associated with a rapid increase in body weight and an increase in diurnal proximal sodium reabsorption, without any change in renal haemodynamics or in the modulation of the renin-angiotensin aldosterone system to changes in salt intake. A compensatory increase in brain natriuretic peptide levels was observed. In spite of sodium retention, pioglitazone dissociated the blood-pressure response to salt and abolished salt sensitivity in salt-sensitive individuals.

CONCLUSIONS/INTERPRETATION

Pioglitazone increases diurnal proximal sodium retention in diabetic and hypertensive individuals. These effects cause fluid retention and may contribute to the increased incidence of congestive heart failure with glitazones.

TRIAL REGISTRATION

ClinicalTrial.gov NCT01090752

FUNDING

Hypertension Research Foundation Lausanne.

Glomerular hyperfiltration and increased proximal sodium reabsorption in subjects with type 2 diabetes or impaired fasting glucose in a population of the African region

BACKGROUND. Glomerular hyperfiltration (GHF) is a well-recognized early renal alteration in diabetic patients. As the prevalence of GHF is largely unknown in populations in the African region with respect to normal fasting glucose (NFG), impaired fasting glucose (IFG) and type 2 diabetes [diabetes mellitus (DM)], we conducted a cross-sectional study in the Seychelles islands among families including at least one member with hypertension. METHODS. The glomerular filtration rate (GFR), effective renal plasma flow (ERPF) and proximal tubular sodium reabsorption were measured using inulin, p-aminohippurate (PAH) and endogenous lithium clearance, respectively. Twenty-four-hour urine was collected on the preceding day. RESULTS. Of the 363 participants (mean age 44.7 years), 6.6% had IFG, 9.9% had DM and 63.3% had hypertension. The prevalence of GHF, defined as a GFR >140 ml/min, was 17.2%, 29.2% and 52.8% in NFG, IFG and DM, respectively (P trend <0.001). Compared to NFG, the adjusted odds ratio for GHF was 1.99 [95% confidence interval (CI) 0.73-5.44] for IFG and 5.88 (2.39-14.45) for DM. Lithium clearance and fractional excretion of lithium were lower in DM and IFG than NFG (P < 0.001). CONCLUSION. In this population of African descent, subjects with impaired fasting glucose or type 2 diabetes had a high prevalence of GHF and enhanced proximal sodium reabsorption. These findings provide further insight on the elevated incidence of nephropathy reported among African diabetic individuals.

Ethnic differences in proximal and distal tubular sodium reabsorption are heritable in black and white populations

BACKGROUND

Segmental handling of sodium along the proximal and distal nephron might be heritable and different between black and white participants.

METHODS

We randomly recruited 95 nuclear families of black South African ancestry and 103 nuclear families of white Belgian ancestry. We measured the (FENa) and estimated the fractional renal sodium reabsorption in the proximal (RNaprox) and distal (RNadist) tubules from the clearances of endogenous lithium and creatinine. In multivariable analyses, we studied the relation of RNaprox and RNadist with FENa and estimated the heritability (h) of RNaprox and RNadist.

RESULTS

Independent of urinary sodium excretion, South Africans (n = 240) had higher RNaprox (unadjusted median, 93.9% vs. 81.0%; P < 0.001) than Belgians (n = 737), but lower RNadist (91.2% vs. 95.1%; P < 0.001). The slope of RNaprox on FENa was steeper in Belgians than in South Africans (-5.40 +/- 0.58 vs. -0.78 +/- 0.58 units; P < 0.001), whereas the opposite was true for the slope of RNadist on FENa (-3.84 +/- 0.19 vs. -13.71 +/- 1.30 units; P < 0.001). h of RNaprox and RNadist was high and significant (P < 0.001) in both countries. h was higher in South Africans than in Belgians for RNaprox (0.82 vs. 0.56; P < 0.001), but was similar for RNadist (0.68 vs. 0.50; P = 0.17). Of the filtered sodium load, black participants reabsorb more than white participants in the proximal nephron and less postproximally.

CONCLUSION

Segmental sodium reabsorption along the nephron is highly heritable, but the capacity for regulation in the proximal and postproximal tubules differs between whites and blacks.

Renal sodium handling in patients with normal pressure glaucoma

Low BP (blood pressure) is a recognized risk factor for some patients with NPG (normal pressure glaucoma). We have shown previously that patients with orthostasis have impaired circadian renal handling of sodium, which may contribute to the low BP. Therefore the aim of the present study was to examine the renal handling of sodium, the circadian variations in BP and the neurohormonal response to an orthostatic test in a selected subpopulation of 18 patients with NPG with vasospastic and orthostatic symptoms, and in 24 healthy control subjects. The variations in BP and renal tubular sodium handling were evaluated using 24 h ambulatory BP recordings, 24 h urine collections and determination of endogenous lithium clearance as a marker of proximal sodium reabsorption. The neurohormonal and BP responses to changes in posture were also determined in a 30 min orthostatic test. This selected group of patients with NPG had lower 24 h ambulatory BPs (P<0.001), and a more pronounced fall in BP when assuming an upright position (P<0.001) compared with controls. FE(Li) (fractional excretion of lithium) was higher in patients with NPG than controls during the day (36.6+/-21.8 compared with 20.4+/-8.7% respectively; P<0.01; values are means+/-S.D.) as well as during the night (38.8+/-41.9 compared with 19.7+/-10.8% respectively; P<0.02), suggesting a reduced reabsorption of sodium in the proximal tubule. This was compensated for by an increased distal reabsorption of sodium in patients with NPG (P<0.01). These data demonstrate that patients with vasospastic NPG have a high excretion of lithium, suggesting reduced sodium reabsorption in the proximal tubule, in spite of a low BP. The abnormal renal sodium handling might contribute to the maintenance of arterial hypotension and progression of the optic nerve damage in these patients.

CYP3A5 and ABCB1 genes influence blood pressure and response to treatment, and their effect is modified by salt

The permeability-glycoprotein efflux-transporter encoded by the multidrug resistance 1 (ABCB1) gene and the cytochromes P450 3A4/5 encoded by the CYP3A4/5 genes are known to interact in the transport and metabolism of many drugs. Recent data have shown that the CYP3A5 genotypes influence blood pressure and that permeability-glycoprotein activity might influence the activity of the renin-angiotensin system. Hence, these 2 genes may contribute to blood pressure regulation in humans. We analyzed the association of variants of the ABCB1 and CYP3A5 genes with ambulatory blood pressure, plasma renin activity, plasma aldosterone, endogenous lithium clearance, and blood pressure response to treatment in 72 families (373 individuals; 55% women; mean age: 46 years) of East African descent. The ABCB1 and CYP3A5 genes interact with urinary sodium excretion in their effect on ambulatory blood pressure (daytime systolic: P=0.05; nighttime systolic and diastolic: P<0.01), suggesting a gene-gene-environment interaction. The combined action of these genes is also associated with postproximal tubular sodium reabsorption, plasma renin activity, plasma aldosterone, and with an altered blood pressure response to the angiotensin-converting enzyme inhibitor lisinopril (P<0.05). This is the first reported association of the ABCB1 gene with blood pressure in humans and demonstration that genes encoding for proteins metabolizing and transporting drugs and endogenous substrates contribute to blood pressure regulation.

Association Between Arterial Properties and Renal Sodium Handling in a General Population

Mean arterial pressure drives pressure-natriuresis and determines arterial structure and function. In a population sample, we investigated the relation between arterial characteristics and renal sodium handling as assessed by the clearance of endogenous lithium. We ultrasonographically measured diameter, cross-sectional compliance (CC) and distensibility (DC) of the carotid, brachial, and femoral arteries in 1069 untreated subjects (mean age: 41.6 years; 50.1% women; 18.8% hypertensive subjects). While accounting for covariates and standardizing for the sodium excretion rate in both sexes, CC and DC of the femoral artery increased with higher fractional distal sodium reabsorption. Differences associated with a 1-SD change in fractional distal reabsorption of sodium were 51.7 mm(2)/kPax10(-3) (95% CI: 23.9 to 79.5; P=0.0002) and 0.56x10(-3)/kPa (95% CI: 0.17 to 0.94; P=0.004) for femoral CC and DC, respectively. In women as well as in men, a 1-SD increment in fractional proximal sodium reabsorption was associated with decreases in femoral and brachial diameter, amounting to 111.6 mum (95% CI: 38.2 to 185.1; P=0.003) and 52.5 mum (95% CI: 10.0 to 94.9; P=0.016), respectively. There was no consistent association between the properties of the elastic carotid artery and renal sodium handling. In conclusion, higher fractional sodium reabsorption in the distal nephron is associated with higher femoral CC and DC, and higher proximal sodium reabsorption is associated with decreased brachial and femoral diameters. These findings demonstrate that there might be an influence of renal sodium handling on arterial properties or vice versa or that common mechanisms might influence both arterial and renal function.

Metoprolol prevents sodium retention induced by lower body negative pressure in healthy men

BACKGROUND

Lower body negative pressure (LBNP) has been shown to induce a progressive activation of neurohormonal systems, and a renal tubular and hemodynamic response that mimics the renal adaptation observed in congestive heart failure (CHF). As beta-blockers play an important role in the management of CHF patients, the effects of metoprolol on the renal response were examined in healthy subjects during sustained LBNP.

METHODS

Twenty healthy male subjects were randomized in this double blind, placebo versus metoprolol 200 mg once daily, study. After 10 days of treatment, each subject was exposed to 3 levels of LBNP (0, -10, and -20 mbar) for 1 hour, each level of LBNP being separated by 2 days. Neurohormonal profiles, systemic and renal hemodynamics, as well as renal sodium handling were measured before, during, and after LBNP.

RESULTS

Blood pressure and heart rate were significantly lower in the metoprolol group throughout the study (P < 0.01). GFR and RPF were similar in both groups at baseline, and no change in renal hemodynamic values was detected at any level of LBNP. However, a reduction in sodium excretion was observed in the placebo group at -20 mbar, whereas no change was detected in the metoprolol group. An increase in plasma renin activity was also observed at -20 mbar in the placebo group that was not observed with metoprolol.

CONCLUSION

The beta-blocker metoprolol prevents the sodium retention induced by lower body negative pressure in healthy subjects despite a lower blood pressure. The prevention of sodium retention may be due to a blunting of the neurohormonal response. These effects of metoprolol on the renal response to LBNP may in part explain the beneficial effects of this agent in heart failure patients.

Effects of the peroxisomal proliferator-activated receptor-gamma agonist pioglitazone on renal and hormonal responses to salt in healthy men

Glitazones are used in the treatment of type 2 diabetes as efficient insulin sensitizers. They can, however, induce peripheral edema through an unknown mechanism in up to 18% of cases. In this double-blind, randomized, placebo-controlled, four-way, cross-over study, we examined the effects of a 6-wk administration of pioglitazone (45 mg daily) or placebo on the blood pressure, hormonal, and renal hemodynamic and tubular responses to a low (LS) and a high (HS) sodium diet in healthy volunteers. Pioglitazone had no effect on the systemic and renal hemodynamic responses to salt, except for an increase in daytime heart rate. Urinary sodium excretion and lithium clearance were lower with pioglitazone, particularly with the LS diet (P < 0.05), suggesting increased sodium reabsorption at the proximal tubule. Pioglitazone significantly increased plasma renin activity with the LS (P = 0.02) and HS (P = 0.03) diets. Similar trends were observed with aldosterone. Atrial natriuretic levels did not change with pioglitazone. Body weight increased with pioglitazone in most subjects. Pioglitazone stimulates plasma renin activity and favors sodium retention and weight gain in healthy volunteers. These effects could contribute to the development of edema in some subjects treated with glitazones.

Angiotensin II receptor blockade prevents acute renal sodium retention induced by low levels of orthostatic stress

BACKGROUND

Depending on its magnitude, lower body negative pressure (LBNP) has been shown to induce a progressive activation of neurohormonal, renal tubular, and renal hemodynamic responses, thereby mimicking the renal responses observed in clinical conditions characterized by a low effective arterial volume such as congestive heart failure. Our objective was to evaluate the impact of angiotensin II receptor blockade with candesartan on the renal hemodynamic and urinary excretory responses to a progressive orthostatic stress in normal subjects.

METHODS

Twenty healthy men were submitted to three levels of LBNP (0, -10, and -20 mbar or 0, -7.5, and -15 mm Hg) for 1 hour according to a crossover design with a minimum of 2 days between each level of LBNP. Ten subjects were randomly allocated to receive a placebo and ten others were treated with candesartan 16 mg orally for 10 days before and during the three levels of LBNP. Systemic and renal hemodynamics, renal sodium excretions, and the hormonal response were measured hourly before, during, and for 2 hours after LBNP.

RESULTS

During placebo, LBNP induced no change in systemic and renal hemodynamics, but sodium excretion decreased dose dependently with higher levels of LBNP. At -20 mbar, cumulative 3-hour sodium balance was negative at -2.3 +/- 2.3 mmol (mean +/- SEM). With candesartan, mean blood pressure decreased (76 +/- 1 mm Hg vs. 83 +/- 3 mm Hg, candesartan vs. placebo, P < 0.05) and renal plasma flow increased (858 +/- 52 mL/min vs. 639 +/- 36 mL/min, candesartan vs. placebo, P < 0.05). Glomerular filtration rate (GFR) was not significantly higher with candesartan (127 +/- 7 mL/min in placebo vs. 144 +/- 12 mL/min in candesartan). No significant decrease in sodium and water excretion was found during LBNP in candesartan-treated subjects. At -20 mbar, the 3-hour cumulative sodium excretion was + 4.6 +/- 1.4 mmol in the candesartan group (P= 0.02 vs. placebo).

CONCLUSION

Selective blockade of angiotensin II type 1 (AT1) receptors with candesartan increases renal blood flow and prevents the antinatriuresis during sustained lower body negative pressure despite a modest decrease in blood pressure. These results thus provide interesting insights into potential benefits of AT1 receptor blockade in sodium-retaining states such as congestive heart failure.

Renal hemodynamic and tubular responses to salt in women using oral contraceptives

BACKGROUND

The use of oral contraceptives is associated with an increased risk of developing hypertension but the mechanisms of this hypertensive effect are not completely defined. The purpose of the present study was to assess prospectively the systemic and renal hemodynamic and tubular responses to salt in women taking oral contraceptives.

METHODS

Twenty seven young healthy normotensive women taking oral contraceptives containing monophasic combination of 30 microg ethynilestradiol and 150 microg desogestrel for>6 months were enrolled. All women were assigned at random to receive a low (40 mmol/day) or a high (250 mmol/day) sodium diet for 1 week on two consecutive menstrual cycles during the active oral contraceptive phase. At the end of each diet period, 24-hour ambulatory blood pressure, renal hemodynamics, sodium handling, and hormonal profile were measured.

RESULTS

The blood pressure response to salt on oral contraceptives was characterized by a salt-resistant pattern with a normal circadian rhythm. Salt loading results in an increase in glomerular filtration rate (GFR) (P < 0.05 vs. low salt), with no change in the renal plasma flow, thus leading to an increase in the filtration fraction (P < 0.05). At the tubular level, women on oral contraceptives responded to a low salt intake with a marked increased in proximal sodium conservation (P < 0.01 vs. high salt) and with an almost complete reabsorption of sodium reaching the distal tubule. After sodium loading, both the proximal and the distal reabsorption of sodium decreased significantly (P < 0.01).

CONCLUSION

The use of oral contraceptives is not associated with an increased blood pressure response to salt in young normotensive women. However, oral contraceptives affect the renal hemodynamic response to salt, a high salt intake leading to an increase in GFR and filtration fraction. This effect is possibly mediated by the estrogen-induced activation of the renin-angiotensin system. Oral contraceptives also appear to increase the tubular responsiveness to changes in sodium intake. Taken together, these data point out evidence that synthetic sex steroids have a significant impact on renal function in women. The renal effects of oral contraceptives should be taken into account when managing young women with renal diseases.

Renal segmental tubular response to salt during the normal menstrual cycle

BACKGROUND

It has been suggested that women gain weight and develop peripheral edema during the luteal phase of the menstrual cycle because they tend to retain sodium and water. However, there is actually no clear evidence for physiological, cyclic variations in renal sodium handling during the menstrual cycle. We prospectively assessed the changes in segmental renal sodium handling occurring during the menstrual cycle in response to changes in salt intake.

METHODS

Thirty-five normotensive women were enrolled. Seventeen women were randomized and studied in the follicular and 18 in the luteal phases of their menstrual cycle. All women were assigned at random to receive a low (40 mmol/day) or a high (250 mmol/day) sodium diet for seven days on two consecutive menstrual cycles. Renal sodium handling and hemodynamics were measured at the end of each diet period.

RESULTS

The changes in sodium intake induced comparable variations in sodium excretion in both phases of the menstrual cycle. In the follicular phase, the increase in salt intake was associated with no change in renal hemodynamics, an increased fractional excretion of lithium (FELi) and a decreased fractional distal reabsorption of sodium (FDRNa), suggesting that sodium reabsorption is reduced both in the proximal and the distal tubules. In contrast, in the luteal phase, the renal response to salt was characterized by a significant renal vasodilation and a marked salt escape from the distal nephron, compared to the women investigated in the follicular phase (P < 0.01). Sodium reabsorption by the proximal nephron was not reduced as indicated by the unchanged FELi.

CONCLUSIONS

These results show that the segmental renal handling of sodium differs markedly in the two phases of the menstrual cycle. They suggest that the female hormones modulate the renal handling of sodium at the proximal and distal segments of the nephron in young normotensive women.

Renal and neurohormonal responses to increasing levels of lower body negative pressure in men

BACKGROUND

The stimulation of efferent renal sympathetic nerve activity induces sequential changes in renin secretion, sodium excretion, and renal hemodynamics that are proportional to the magnitude of the stimulation of sympathetic nerves. This study in men investigated the sequence of the changes in proximal and distal renal sodium handling, renal and systemic hemodynamics, as well as the hormonal profile occurring during a sustained activation of the sympathetic nervous system induced by various levels of lower body negative pressure (LBNP).

METHODS

Ten healthy subjects were submitted to three levels of LBNP ranging between 0 and -22.5 mm Hg for one hour according to a triple crossover design, with a minimum of five days between each level of LBNP. Systemic and renal hemodynamics, renal water and sodium handling (using the endogenous lithium clearance technique), and the neurohormonal profile were measured before, during, and after LBNP.

RESULTS

LBNP (0 to -22.5 mm Hg) induced an important hormonal response characterized by a significant stimulation of the sympathetic nervous system and gradual activations of the vasopressin and the renin-angiotensin systems. LBNP also gradually reduced water excretion and increased urinary osmolality. A significant decrease in sodium excretion was apparent only at -22.5 mm Hg. It was independent of any change in the glomerular filtration rate and was mediated essentially by an increased sodium reabsorption in the proximal tubule (a significant decrease in lithium clearance, P < 0.05). No significant change in renal hemodynamics was found at the tested levels of LBNP. As observed experimentally, there appeared to be a clear sequence of responses to LBNP, the neurohormonal response occurring before the changes in water and sodium excretion, these latter preceding any change in renal hemodynamics.

CONCLUSIONS

These data show that the renal sodium retention developing during LBNP, and thus sympathetic nervous stimulation, is due mainly to an increase in sodium reabsorption by the proximal segments of the nephron. Our results in humans also confirm that, depending on its magnitude, LBNP leads to a step-by-step activation of neurohormonal, renal tubular, and renal hemodynamic responses.

Validation of an HPLC method for the determination of urinary and plasma levels of N1-methylnicotinamide, an endogenous marker of renal cationic transport and plasma flow

N1-Methylnicotinamide (NMN) is an endogenous cationic metabolite of nicotinamide (niacine, vitamine PP) whose renal clearance reflects both the capacity of the renal tubular transport system to secrete organic cations and renal plasma flow. NMN is present in human plasma and urine at the 1-117-ng ml(-1) and 0.5-25-microg ml(-1) concentration range, respectively, and its level depends notably on pathophysiological (age, renal or hepatic diseases) conditions. We report the optimization and validation of an HPLC method for the measurement of endogenous NMN in biological fluids after derivatization into a fluorescent compound. Plasma is first deproteinized with TCA 20% and the urine diluted 1:10 with HCI 10(-4) M prior to the derivatization procedure, which includes a condensation reaction of NMN with acetophenone in NaOH at 0 degrees C, followed by dehydration in formic acid and subsequent formation of the fluorescent 1,6-naphthyridine derivatives after heating samples in a boiling water bath. The synthetic homologous derivative N1-ethylnicotinamide (NEN) reacts similarly and is added as internal standard into the biological fluid. The reaction mixture is subjected to reverse phase high performance liquid chromatography on a Nucleosil 100-C18 column using a mobile phase (acetonitrile 22%, triethylamine 0.5%, 0.01 M sodium heptanesulfonate adjusted to pH 3.2), delivered isocratically at a flow rate of 1 ml min(-1), NMN and NEN are detected at 7.8 and 10 min by spectrofluorimetry with excitation and emission wavelengths set at 366 and 418 nm, respectively. The addition-calibration method is used with plasma and urine pools. Calibration curves (using the internal standard method) are linear (r2 > 0.997) at concentrations up to 109 ng ml(-1) and 15.7 microg ml(-1) in plasma and urine, respectively. Both intra- and inter-assay precision of plasma control samples at 10, 50 and 90 ng ml(-1) were lower than 3.3% and concentrations not deviating more than 2.7% from their nominal values. In urine intra- and inter-assay CVs of control samples at 1, 5 and 9 microg ml(-1) are lower than 8.3%, with concentrations not deviating more than -9.0 to +11.8% from their nominal values. This analytical method has therefore the required sensitivity and selectivity to measure NMN in plasma and urine, enabling the non-invasive determination of the tubular secretory capacity of the kidney and the renal plasma flow.

Renal sodium handling in acute and chronic salt loading/depletion protocols: the confounding influence of acute water loading

OBJECTIVES

Renal tubular sodium handling was measured in healthy subjects submitted to acute and chronic salt-repletion/salt-depletion protocols. The goal was to compare the changes in proximal and distal sodium handling induced by the two procedures using the lithium clearance technique.

METHODS

In nine subjects, acute salt loading was obtained with a 2 h infusion of isotonic saline, and salt depletion was induced with a low-salt diet and furosemide. In the chronic protocol, 15 subjects randomly received a low-, a regular- and a high-sodium diet for 1 week. In both protocols, renal and systemic haemodynamics and urinary electrolyte excretion were measured after an acute water load. In the chronic study, sodium handling was also determined, based on 12 h day- and night-time urine collections.

RESULTS

The acute and chronic protocols induced comparable changes in sodium excretion, renal haemodynamics and hormonal responses. Yet, the relative contribution of the proximal and distal nephrons to sodium excretion in response to salt loading and depletion differed in the two protocols. Acutely, subjects appeared to regulate sodium balance mainly by the distal nephron, with little contribution of the proximal tubule. In contrast, in the chronic protocol, changes in sodium reabsorption could be measured both in the proximal and distal nephrons. Acute water loading was an important confounding factor which increased sodium excretion by reducing proximal sodium reabsorption. This interference of water was particularly marked in salt-depleted subjects.

CONCLUSION

Acute and chronic salt loading/salt depletion protocols investigate different renal mechanisms of control of sodium balance. The endogenous lithium clearance technique is a reliable method to assess proximal sodium reabsorption in humans. However, to investigate sodium handling in diseases such as hypertension, lithium should be measured preferably on 24 h or overnight urine collections to avoid the confounding influence of water.

Proximal sodium reabsorption: An independent determinant of blood pressure response to salt

The purpose of this study was to evaluate the contribution of renal sodium handling by the proximal tubule as an independent determinant of blood pressure responsiveness to salt in hypertension. We measured blood pressure (BP), renal hemodynamics, and segmental renal sodium handling (with lithium used as a marker of proximal sodium reabsorption) in 38 hypertensive patients and 27 normotensive subjects (15 young and 12 age-matched) on a high and low sodium diet. In control subjects, changing the diet from a low to a high sodium content resulted in no change in BP and increases in glomerular filtration rate (P<0.05), renal plasma flow (P<0.05), and fractional excretion of lithium (FE(Li), P<0.01). In hypertensive patients, comparable variations of sodium intake induced an increase in BP with no change in renal hemodynamics and proximal sodium reabsorption. When analyzed by tertiles of their BP response to salt, salt-insensitive hypertensive patients of the first tertile disclosed a pattern of adaptation of proximal sodium reabsorption comparable to that of control subjects, whereas the most salt-sensitive patients of the third tertile had an inverse pattern with a high FE(Li) on low salt and a lower FE(Li) on high salt, suggesting an inappropriate modulation of proximal sodium reabsorption. The BP response to salt correlated positively with age (r=0.34, P=0.036) and negatively with the changes in FE(Li) (r=-0.37, P=0.029). In a multivariate analysis, the changes in FE(Li) were significantly and independently associated with the salt-induced changes in BP. These results suggest that proximal sodium reabsorption is an independent determinant of the BP response to salt in hypertension.

Salt- and angiotensin II-dependent variations in amiloride-sensitive rectal potential difference in mice

1. In the rectum and distal nephron, sodium reabsorption is mediated by the amiloride-sensitive epithelial sodium channel (ENaC). The ENaC-mediated sodium transport is electrogenic and creates an amiloride-sensitive transepithelial potential difference (PD). 2. We have evaluated the salt- and angiotensin (Ang)II-dependent variations in amiloride-sensitive rectal PD in mice and assessed their relationship with renal sodium handling. 3. Rectal PD was measured in vivo in mice maintained on a medium-, low- or high-sodium diet. On a medium-salt diet, the mean (+/- SEM) amiloride-sensitive PD was larger in the afternoon than in the morning (-26.1 +/- 0.9 and -11.2 +/- 0.7 mV, respectively; P = 0.001), indicating a circadian cyclicity. Rectal PD increased on a low-sodium diet and decreased on a high-sodium diet. 4. Amiloride-sensitive rectal PD correlated significantly with the urinary Na+/K+ ratio (P < 0.001) and with sodium reabsorption in the distal nephron as measured by the lithium clearance technique (P < 0.001). 5. In mice treated with an AngII AT1 receptor antagonist, amiloride-sensitive rectal PD was increased in the afternoon compared with controls (-32.8 +/- 2.0 vs -24.4 +/- 0.9, respectively; P < 0.001). 6. At high doses, AngII decreased the amiloride-sensitive rectal PD and this effect was blunted by an AT1 receptor antagonist. 7. These results show the presence of a salt-dependent daily cyclicity of sodium transport in the mouse rectum that follows circadian changes in sodium handling in the distal nephron. Angiotensin II appears to modulate this diurnal pattern of rectal amiloride-sensitive sodium transport.

Trace lithium in mood disorders

BACKGROUND

Variations in trace (endogenous) lithium exchanges have been postulated to play a role in the pathophysiology of affective diseases. This prospective study aimed to check whether plasma, erythrocytes and urine trace lithium levels were altered in mood disorders.

METHODS

Trace lithium was determined by atomic absorption spectrophotometry in patients without mood stabilizing drugs or somatic diseases, hospitalized for bipolar affective disorders, major depressive episodes, and other psychiatric disorders with depressive features. Patients admitted for psychotic disorders without mood alterations and healthy volunteers served as controls.

RESULTS

There were no differences in trace lithium status between the groups. Erythrocytes/plasma ratios appeared higher than described on therapeutic lithium (1.6+/-0.7, N = 199).

LIMITATIONS

The study had sufficient power to detect clinically significant differences in whole body lithium handling between the groups. However, it did not address alterations of lithium exchanges across neuronal membranes or the blood-brain barrier.

CONCLUSIONS

Alterations of membrane exchanges hypothetically associated with mood disorders are not reflected in plasma or erythrocytes trace lithium levels. The occurrence of mood disorders seems not to be related to abnormalities in endogenous lithium.

Effects of a dual inhibitor of angiotensin converting enzyme and neutral endopeptidase, MDL 100,240, on endocrine and renal functions in healthy volunteers

OBJECTIVE

To investigate the endocrine and renal effects of the dual inhibitor of angiotensin converting enzyme and neutral endopeptidase, MDL 100,240.

DESIGN

A randomized, placebo-controlled, crossover study was performed in 12 healthy volunteers.

METHODS

MDL 100,240 was administered intravenously over 20 min at single doses of 6.25 and 25 mg in subjects with a sodium intake of 280 (n = 6) or 80 (n = 6) mmol/day. Measurements were taken of supine and standing blood pressure, plasma angiotensin converting enzyme activity, angiotensin II, atrial natriuretic peptide, urinary atrial natriuretic peptide and cyclic GMP excretion, effective renal plasma flow and the glomerular filtration rate as p-aminohippurate and inulin clearances, electrolytes and segmental tubular function by endogenous lithium clearance.

RESULTS

Supine systolic blood pressure was consistently decreased by MDL 100,240, particularly after the high dose and during the low-salt intake. Diastolic blood pressure and heart rate did not change. Plasma angiotensin converting enzyme activity decreased rapidly and dose-dependently. In both the high- and the low-salt treatment groups, plasma angiotensin II levels fell and renin activity rose accordingly, while plasma atrial natriuretic peptide levels remained unchanged. In contrast, urinary atrial natriuretic peptide excretion increased dose-dependently under both diets, as did urinary cyclic GMP excretion. Effective renal plasma flow and the glomerular filtration rate did not change. The urinary flow rate increased markedly during the first 2 h following administration of either dose of MDL 100,240 (P < 0.001) and, similarly, sodium excretion tended to increase from 0 to 4 h after the dose (P = 0.07). Potassium excretion remained stable. Proximal and distal fractional sodium reabsorption were not significantly altered by the treatment. Uric acid excretion was increased. The safety and clinical tolerance of MDL 100,240 were good.

CONCLUSIONS

The increased fall in blood pressure in normal volunteers together with the preservation of renal hemodynamics and the increased urinary volume, atrial natriuretic peptide and cyclic GMP excretion distinguish MDL 100,240 as a double-enzyme inhibitor from inhibitors of the angiotensin converting enzyme alone. The differences appear to be due, at least in part, to increased renal exposure to atrial natriuretic peptide following neutral endopeptidase blockade.

Effect of indomethacin on the renal response to angiotensin II receptor blockade in healthy subjects

BACKGROUND

Non-steroidal anti-inflammatory drugs are known to promote sodium retention and to blunt the blood pressure lowering effects of several classes of antihypertensive agents including beta-blockers, diuretics and angiotensin converting enzyme (ACE) inhibitors. The purpose of the present study was to investigate the acute and sustained effects of indomethacin on the renal response to the angiotensin II receptor antagonist valsartan and to the ACE inhibitor enalapril.

METHODS

Twenty normotensive subjects maintained on fixed sodium intake (100 mmol sodium/day) were randomized to receive for one week: valsartan 80 mg o.d., enalapril 20 mg o.d., valsartan 80 mg o.d. + indomethacin 50 mg bid and enalapril 20 mg o.d. + indomethacin 50 mg bid. This single-blind study was designed as a parallel (valsartan vs. enalapril) and cross-over trial (valsartan or enalapril vs. valsartan + indomethacin or enalapril + indomethacin). Renal hemodynamics and urinary electrolyte excretion were measured for six hours after the first and seventh administration of each treatment regimen.

RESULTS

The results show that valsartan and enalapril have comparable renal effects characterized by no change in glomerular filtration rate and significant increases in renal plasma flow and sodium excretion. The valsartan- and enalapril-induced renal vasodilation is not significantly blunted by indomethacin. However, indomethacin similarly abolishes the natriuresis induced by the angiotensin II antagonist and the ACE inhibitor.

CONCLUSIONS

This observation suggests that although angiotensin receptor antagonists do not affect prostaglandin metabolism, the administration of a non-steroidal anti-inflammatory drug blunts the natriuretic response to angiotensin receptor blockade.

Circadian variations of renal sodium handling in patients with orthostatic hypotension

BACKGROUND

Sodium wasting during the night has been postulated as a potential pathophysiological mechanism in patients suffering from orthostatic hypotension due to severe autonomic deficiency.

METHODS

In this study, the diurnal variations in creatinine clearance, sodium excretion and segmental renal tubular handling of sodium were evaluated in 18 healthy subjects and 20 young patients with orthostatic hypotension (OH). In addition, 24-hour ambulatory blood pressure and the neuro-hormonal response to changes in posture were determined. The patients and their controls were studied on a free sodium intake. In a second protocol, 10 controls and 10 patients were similarly investigated after one week of a high salt diet (regular diet + 6 g NaCl/day).

RESULTS

Our results demonstrate that, in contrast to normal subjects in whom no significant changes in glomerular filtration, sodium excretion and segmental sodium reabsorption were observed throughout the day, patients with OH were characterized by a significant increase in glomerular filtration rate during the nighttime (P = 0.03) and significant increases in urinary lithium excretion (P < 0.05) and lithium clearance (P = 0.05) during the night, suggesting a decreased proximal reabsorption of sodium. On a high sodium diet, the symptoms of orthostatic hypotension and the circadian variations in sodium reabsorption were significantly blunted.

CONCLUSIONS

These results suggest that, while the patient is in a supine position the effective blood volume of those with OH becomes excessive due to the increased venous return. Hence, the kidney responds with an increase in glomerular filtration and a relative escape of sodium from the proximal tubular segments. These circadian variations in renal sodium handling may contribute to the maintenance of the orthostatic syndrome.

Determination of trace lithium in human erythrocytes by electrothermal atomic-absorption spectrometry with pyrocoated graphite tubes and integrated platform

Electrothermal graphite-furnace atomic-absorption spectroscopy with pyrocoated graphite tubes, integrated platform and matrix modification was used to determine submicromolar concentrations of trace lithium in human red blood cells. Matrix-matched samples were used to establish calibration curves for concentrations up to 0.58 microM (addition-calibration method) with satisfactory linearity (r2 > 0.99) and intra- and inter-day variability (CV < 11.4%). The median concentration of trace lithium in the cells of 40 healthy Caucasian volunteers devoid of medical or psychiatric history was 0.23 microM (inter-quartile range 0.20-0.30). The levels of trace lithium in the red blood cells correlated (r2 = 0.83) with plasma concentrations (median 0.13 microM, inter-quartile range 0.11-0.19) measured in the same blood sample. Dietary factors (e.g. consumption of lithium-containing mineral water) affected both levels. The red blood cell/plasma lithium ratio had a median value of 1.57 (inter-quartile range 1.16-2.07), implying that trace lithium is accumulated in erythrocytes. This contrasts with most reports of red blood cell/plasma ratio, measured during therapeutic treatment with lithium, for which the average value is 0.5-0.8, albeit for much higher concentrations of lithium (approx. 500-800 microM). The proposed analytical method has the required sensitivity and accuracy for determination of trace lithium in red blood cells and makes it possible to perform epidemiological studies to assess human exposure to environmental lithium in diet and beverages, and inter-individual variations in trans-membrane and renal lithium kinetics at the submicromolar level.