Mannitol stimulates atrial natriuretic peptide release in humans

The ratio of the blood urea nitrogen/creatinine index in patients with acute renal failure is decreased due to dextran or mannitol

Acute renal failure (ARF) induced by dextran or mannitol is a lethal adverse effect, and hemodialysis or plasma exchange is recommended to avoid fatal ARF. This report describes 2 cases of ARF; one caused by dextran and the other by mannitol. Both showed decreases in the blood urea nitrogen (BUN)/creatinine ratios after the administration of these reagents. They immediately recovered to the level of creatinine on admission after the administration of these reagents was stopped, without hemodialysis or plasma exchange. Decreases in the BUN/creatinine ratio might be a useful index for the diagnosis of ARF is caused by these reagents.

Variation in osmotic response to sustained mannitol administration

BACKGROUND

Osmotic agents such as mannitol remain a mainstay in the management of cerebral edema and raised intracranial pressure. Some patients do not respond to sustained mannitol administration with the expected rise in serum osmolality, and this may correlate with lack of therapeutic efficacy.

OBJECTIVE

To examine the variation in osmotic response to mannitol therapy and identify factors associated with a lack of an osmotic response to sustained mannitol administration.

METHODS

Data on consecutive patients admitted to a Neurology/Neurosurgery Intensive Care Unit who received scheduled doses of mannitol for at least 48 h were extracted from a prospectively collected database. All patients received intravenous isotonic saline solutions and had serial measurements of serum sodium and osmolality, at least twice daily. Non-responders were defined using two thresholds, a rise in serum sodium of < or =1 or < or =5 mEq/l over the 48-hour period.

RESULTS

The cohort included 167 patients the majority with intracerebral and subarachnoid hemorrhage and brain tumors. 73 patients (44%) did not respond to mannitol with a rise in sodium of > or =5 mEq/l, and 37 (22%) did not see a rise of 1 mEq/l over 48 h of treatment. There were minor differences between responders and non-responders (> or =5 mEq/l) in terms of age (56 +/- 15 vs. 48 +/- 14), total mannitol dose (0.9 +/- 0.2 vs. 0.7 +/- 0.2 g/kg), and cumulative fluid balance at 72 h (91 +/- 1653 vs. -610 +/- 1692 ml). Multivariate analysis found that younger age, lower weight-adjusted mannitol dose, and more negative fluid balance were associated with lack of osmotic response.

DISCUSSION

A substantial proportion of patients receiving sustained mannitol do not manifest the expected osmotic response. This lack of response may correlate with the failure of clinical efficacy seen in a subgroup of patients, who then require alternate agents such as hypertonic saline. This association merits further exploration.

Atrial natriuretic peptide and related peptides

In recent years, biomarkers have been recognized as important tools for diagnosis, risk stratification, and therapeutic decision-making in cardiovascular diseases. Currently, the clinical potential of several natriuretic peptides is under scientific investigation. The well-known counter-regulatory hormones are atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), C-type natriuretic peptide (CNP), dendroaspis natriuretic peptide (DNP) and urodilatin, which play an important role in the homeostasis of body fluid volume. ANP and BNP have already been demonstrated to have diagnostic usefulness in a great number of studies, which have progressed from bench to bedside. This article summarizes existing data on ANP and related peptides in cardiovascular and other disorders, and outlines the potential clinical usefulness of these markers.

Clin Chem Lab Med 2007;45:1259–67.

Radiocontrast-induced natriuresis associated with increased urinary urodilatin excretion

OBJECTIVE

Intravascular radiocontrast agents induce a pronounced diuresis. The aim of the present study was to investigate the (patho-)physiological mechanisms of the radiocontrast-induced diuresis.

DESIGN

The fractional excretion of sodium, the urinary excretion of the renal natriuretic peptide urodilatin and the plasma concentration of atrial natriuretic peptide were measured in 42 unselected patients immediately before and after intravascular radiocontrast administration during coronary angiography.

SETTING

Cardiac catheterization laboratory of a university hospital.

RESULTS

After angiography both the plasma concentration of atrial natriuretic peptide (median post-pre difference: 3.9 pmol L(-1), quartiles -1.2; 7.0) and the urinary excretion of urodilatin (median post-pre difference: 67.0 nmol urodilatin/mol creatinine, quartiles 39.7; 152.1) were increased. The urinary urodilatin excretion was correlated with an increase in the fractional excretion of sodium (median post-pre difference: 1.7%, quartiles 0.6; 3.1). There was no correlation between the serum concentration of atrial natriuretic peptide and urinary sodium excretion. For the radiocontrast-induced increase in both urodilatin and sodium excretion there was no indication for differences between patients without (31) and with (11) intravenous saline infusion.

CONCLUSION

The radiocontrast-induced diuresis is a natriuresis which is associated with an increased urinary excretion of urodilatin. The association between natriuresis and urinary urodilatin excretion irrespective of baseline volume status corroborates the hypothesis that urodilatin contributes to the sodium excretion after radiocontrast administration in a paracrine manner. This finding has pathophysiological and potentially therapeutic implications in radiocontrast-induced nephropathy.

Quantification and predictors of plasma volume expansion from mannitol treatment

OBJECTIVE

To determine the effects of acute hypertonic mannitol infusion on intravascular volume expansion and to identify potential predictors of hypervolemia.

DESIGN

Measurements of plasma volume and volume regulatory hormones were performed in healthy volunteers before and over 90 min after acute infusion of 20% mannitol solution in a therapeutic dose of 0.5 g/kg body weight, equalling an average infusion volume of 180 ml.

SETTING

Clinical research unit in an 800-bed teaching hospital in the eastern part of Switzerland.

PARTICIPANTS

Eight normal male volunteers.

MEASUREMENTS AND RESULTS

Baseline plasma volume was determined by the indocyanine green dye dilution technique. Serial plasma protein measurements were performed after mannitol infusion to calculate intravascular volume changes. Mannitol administration resulted in a plasma expansion that persisted for more than 90 min and peaked at 112% of the baseline plasma volume 15 min after infusion. Concomitantly, an increase in systolic blood pressure and a fall in plasma sodium concentration occurred. Pharmacokinetic analyses of mannitol distribution and elimination revealed a close relation between plasma volume expansion and mannitol serum concentrations. While renin activity and aldosterone concentrations were suppressed proportionally to the intravascular volume increase, antidiuretic hormone was increased despite notable volume expansion and hyponatremia. Similarly, a rise in atrial natriuretic peptide was detected.

CONCLUSIONS

Therapeutic doses of hypertonic mannitol cause substantial plasma volume expansion, resulting in increased blood pressure. Plasma volume expansion is related to mannitol serum concentrations and mannitol clearance determines the time required to restore normovolemia. ADH and ANP are potentially aggravating factors of mannitol-induced hyponatremia.

Prevention of cisplatin nephrotoxicity by exogenous atrial natriuretic peptide

The ability of atrial natriuretic peptide (ANP) to prevent cisplatin-induced nephrotoxicity was compared to the protective effect of 3% NaCl. ANP (1 microgram/kg/min), 3% NaCl or peptide buffer vehicle (50 microliters/min) were infused for 45 min to conscious unrestrained rats immediately after cisplatin administration (5 mg/kg i.v.). Measurements taken 72 h after drug treatment indicated that compared to animals receiving cisplatin only, ANP co-treated rats had lower post-treatment plasma creatinine concentrations (0.70 +/- 0.07 vs 1.3 +/- 0.17 mg/dl; P < 0.05), blood urea nitrogen (BUN) concentrations (44.2 +/- 5.8 vs. 65.5 +/- 2.1 mg/dl; P < 0.05) and higher post-treatment glomerular filtration rates (GFR) (0.71 +/- 0.18 vs. 0.14 +/- 0.03 ml/min; P < 0.05). ANP was as effective as 3% NaCl in preventing cisplatin nephrotoxicity in this model. The effect of ANP co-treatment on the anti-tumor activity of cisplatin was also examined using the Walker 256 carcinosarcoma model. ANP treatment did not result in any observable loss in anti-tumor activity. When ANP was administered 72 h after cisplatin treatment, improvement in GFR was observed for the duration of the infusion, confirming the beneficial effect of ANP on cisplatin-damaged kidneys. ANP may have a role in the treatment and prevention of cisplatin nephrotoxicity especially in clinical situations where treatment with a large fluid volume is contraindicated.

The role of the renin-angiotensin system in cisplatin nephrotoxicity

The role of the renin-angiotensin system (RAS) in the pathogenesis of cisplatin nephrotoxicity was evaluated in an experimental rat model using a specific, nonpeptide angiotensin II(AII) receptor blocker, losartan. Rats were treated with a single dose of losartan (at 10 mg/kg and 30 mg/kg, i.p.) or saline, 2 h prior to cisplatin administration (5 mg/kg, i.p.). Renal function was assessed 3 and 7 days after cisplatin treatment. A second group of rats received losartan (10 mg/kg, i.p.) or saline, 2 h prior to cisplatin administration (5 mg/kg, i.p.), and losartan (10 mg/kg, i.p.) or saline daily for 6 days after cisplatin treatment. Renal function was assessed on day 7. Neither high- nor low-dose losartan pretreatment prevented development of cisplatin-induced nephrotoxicity. Blood urea nitrogen (BUN) and plasma creatinine values at 7 days were similar to those of animals receiving cisplatin alone (BUN: 17.12 +/- 1.1 and 22.17 +/- 2.2 vs. 20.58 +/- 2.4 mg/dL; creatinine: 1.04 +/- 0.05 and 0.82 +/- 0.09 vs. 0.84 +/- 0.06 mg/dL). A significant reduction in creatinine clearance with cisplatin treatment was seen 3 days after therapy, which was not prevented by pretreatment with losartan (GFR in controls: 2.1 +/- 0.16 mL/min; cisplatin: 0.24 +/- 0.05; cisplatin plus low-dose losartan: 0.05 +/- 0.03 and cisplatin plus high-dose losartan: 0.37 +/- 0.05). All groups of cisplatin-treated rats displayed systemic signs of cisplatin toxicity: reduced food intake and body weight. Rats receiving chronic losartan treatment had more rapid weight gain and lower BUN and plasma creatinine levels on day 7 than rats receiving cisplatin alone (BUN: 24.0 +/- 2.64 vs. 36.4 +/- 0.91 mg/dL; p < 0.05; plasma creatinine: 0.86 +/- 0.06 vs. 1.15 +/- 0.07 mg/dL; p < 0.05). Acute blockade of the AII receptor with losartan does not alter the onset or severity of cisplatin nephrotoxicity. Chronic blockade of the AII receptor may improve the rate of recovery of renal function in cisplatin-treated rats.