Radioimmunoassays of arginine vasopressin and atrial natriuretic peptide: application of a common protocol for plasma extraction using Sep-Pak C18 cartridges

The interaction of vasopressin and corticosteroids in septic shock: a pilot randomized controlled trial

OBJECTIVES

Vasopressin and corticosteroids are both commonly used adjunctive therapies in septic shock. Retrospective analyses have suggested that there may be an interaction between these drugs, with higher circulating vasopressin levels and improved outcomes in patients treated with both vasopressin and corticosteroids. We aimed to test for an interaction between vasopressin and corticosteroids in septic shock.

DESIGN

Prospective open-label randomized controlled pilot trial.

SETTING

Four adult ICUs in London teaching hospitals.

PATIENTS

Sixty-one adult patients who had septic shock.

INTERVENTIONS

Initial vasopressin IV infusion titrated up to 0.06 U/min and then IV hydrocortisone (50 mg 6 hourly) or placebo. Plasma vasopressin levels were measured at 6-12 and 24-36 hours after hydrocortisone/placebo administration.

MEASUREMENTS AND MAIN RESULTS

Thirty-one patients were allocated to vasopressin + hydrocortisone and 30 patients to vasopressin + placebo. The hydrocortisone group required a shorter duration of vasopressin therapy (3.1 d; 95% CI, 1.1-5.1; shorter in hydrocortisone group) and required a lower total dose of vasopressin (ratio, 0.47; 95% CI, 0.32-0.71) compared with the placebo group. Plasma vasopressin levels were not higher in the hydrocortisone group compared with the placebo group (64 pmol/L difference at 6- to 12-hour time point; 95% CI, -32 to 160 pmol/L). Early vasopressin use was well tolerated with only one serious adverse event possibly related to study drug administration reported. There were no differences in mortality rates (23% 28-day mortality in both groups) or organ failure assessments between the two treatment groups.

CONCLUSIONS

Hydrocortisone spared vasopressin requirements, reduced duration, and reduced dose, when used together in the treatment of septic shock, but it did not alter plasma vasopressin levels. Further trials are needed to assess the clinical effectiveness of vasopressin as the initial vasopressor therapy with or without corticosteroids.

Free radical-mediated lipid peroxidation and systemic nitric oxide bioavailability: implications for postexercise hemodynamics

BACKGROUND

The metabolic vasodilator mediating postexercise hypotension (PEH) is poorly understood. Recent evidence suggests an exercise-induced reliance on pro-oxidant-stimulated vasodilation in normotensive young human subjects, but the role in the prehypertensive state is not known.

METHODS

Nine prehypertensives (mean arterial pressure (MAP), 106 ± 5 mm Hg; 50 ± 10 years old) performed 30 minutes of cycle exercise and a nonexercise trial. Arterial distensibility was characterized by simultaneously recording upper- and lower-limb pulse wave velocity (PWV) via oscillometry. Systemic vascular resistance and conductance were determined by MAP/Q and Q/MAP, respectively. Venous blood was assayed for indirect markers of oxidative stress (lipid hydroperoxides (LOOH); spectrophotometry), plasma nitric oxide (NO) and S-nitrosothiols (fluorometry), atrial natriuretic peptide (ANP), and angiotensin II (ANG-II) (radioimmunoassay).

RESULTS

Exercise reduced MAP (6mm Hg) and vascular resistance (15%) at 60 minutes after exercise, whereas conductance was elevated (20%) (P < 0.05). The hypotension resulted in a lower MAP at 60 and 120 minutes after exercise compared with nonexercise (P < 0.05). Upper-limb PWV was also 18% lower after exercise compared with baseline (P < 0.05). Exercise increased LOOH coincident with the nadir in hypotension and vascular resistance but failed to affect plasma NO or S-nitrosothiols. Exercise-induced increases in LOOH were related to ANG-II (r = 0.97; P < 0.01) and complemented by elevated ANP concentrations.

CONCLUSIONS

These data indicate attenuated vascular resistance after exercise with increased oxidative stress and unchanged NO. Whether free radicals are obligatory for PEH requires further investigation, although it seems that oxidative stress occurs during the hyperemia underlying PEH.

Measurement of arginine vasopressin

Arginine vasopressin (AVP) is a peptide hormone synthesised in the hypothalamus and secreted from nerve terminals within the posterior pituitary gland. Secretion is primarily under osmoregulatory control and levels rise in plasma in response to a body water deficit and are suppressed in response to water overload. The responsive end organ in osmoregulation is the kidney, and an increase in plasma AVP normally results in urine concentration while a decrease results in urine dilution and a diuresis. The hormone is present in urine. The level of AVP in urine is directly related to the prevailing plasma concentration, but is also influenced by urine concentration, osmolal clearance, and renal metabolism. The measurement of AVP in plasma and urine is by radioimmunoassay (RIA). Prior extraction of the hormone is required to remove interfering substances and, particularly for plasma measurements, to concentrate the assayed sample. The secretion of AVP by the posterior pituitary gland is also stimulated by non-osmoregulatory factors such as reduced blood volume, reduced blood pressure, and nausea and is acutely suppressed by an oropharyngeal reflex. Plasma AVP measurement has a role in delineating complex osmoregulatory dysfunction, but protocols for study need to control the non-osmoregulated stimulatory and inhibitory factors. The urine AVP excretion rate corrected for osmolal clearance has a role in the assessment of renal responsiveness to its action.

Thiazolidinediones and the renal and hormonal response to water immersion-induced volume expansion in type 2 diabetes mellitus

Thiazolidinediones cause sodium retention and edema by a direct effect on the kidneys. The aim of this study was to use the technique of head-out water immersion to investigate the effects of rosiglitazone on sodium and volume homeostasis in subjects with type 2 diabetes mellitus. The volume expansion response to water immersion was compared with the response on a non-immersion control day in 12 nondiabetic male subjects and 8 diet-controlled male type 2 diabetic subjects with hourly blood and urine sampling over a 4-h period. This was repeated after both groups had taken 4 mg of rosiglitazone daily for 7 days. Immersion produced a natriuresis in both groups (P < 0.001). An impairment of this natriuresis was seen in the diabetic subjects (P = 0.006). However, when rosiglitazone was taken, there was no significant difference in immersion-induced natriuresis compared with nondiabetic controls (P = 0.2). There was an immersion-induced rise in atrial natriuretic peptide (ANP) and urinary cyclic guanosine monophosphate (cGMP), in the healthy subjects (ANP P = 0.001, cGMP P = 0.043), which was not seen in the diabetic subjects (ANP P = 0.51, cGMP P = 0.74). Rosiglitazone restored the immersion-induced increase in cGMP excretion and rise of ANP in the diabetic group (ANP P = 0.048, cGMP P = 0.009). This study confirms that type 2 diabetic subjects have an impaired natriuretic response to acute volume expansion, which appears to be enhanced rather than diminished by rosiglitazone. This may be related to its effects in increasing natriuretic peptides and restoring the impaired cGMP excretion to volume expansion.

Clinical Features, Diagnosis and Molecular Studies of Familial Central Diabetes Insipidus

BACKGROUND

Familial central diabetes insipidus (DI) is rare and is characterised by polydipsia and polyuria with a variable age of onset. The evaluation of arginine vasopressin (AVP) secretion in these individuals has been reported infrequently and only in adulthood.

OBJECTIVE

To describe the clinical features, diagnosis and molecular investigation of children affected by familial central DI.

METHODS

Functional studies of AVP secretion were undertaken in children from two kindreds with familial central DI. The AVP-neurophysin II (AVP-NPII) gene was also sequenced in symptomatic individuals.

RESULTS

In affected individuals, the result of the water deprivation test may be inconclusive. However, the hypertonic saline test identified both the severe and partial forms of AVP deficiency. A novel mutation of the AVP-NPII gene was identified by direct gene sequencing in both families.

CONCLUSIONS

This report highlights the progressive decline in AVP secretion with increasing age in this disorder and the usefulness of mutational analysis in these families. In symptomatic individuals, the hypertonic saline test may be a useful second-line investigation for functional studies of AVP secretion where molecular diagnostics are unavailable.

Plasma atrial natriuretic peptide in fetuses with cardiac disease

OBJECTIVE

To investigate atrial natriuretic peptide (ANP) levels in fetuses with cardiac defects and to evaluate the relationships between plasma ANP levels and the presence of polyhydramnios.

METHODS

Plasma ANP levels were measured by radioimmunoassay in 27 fetuses with cardiac abnormalities and in 14 normal healthy fetuses.

RESULTS

Fetal plasma ANP levels were similar in the two studied groups (p = 0.18) but they were significantly higher in a subset of cases with cardiac disease and polyhydramnios (n = 7) than in those with cardiac disease and normal amniotic fluid (n = 20; p = 0.036) and controls (p = 0.01).

CONCLUSION

Polyhydramnios in fetuses with heart conditions might be explained by increased fetal diuresis secondary to increased ANP production.

Plasma atrial natriuretic polypeptide in the elderly: age or hypertension?

The effect of age and raised blood pressure on the plasma concentration of atrial natriuretic peptide (ANP) was examined in 20 young (23-49 years), 20 elderly normotensive (71-80 years) and 20 elderly hypertensive (71-82 years, BP > 160/90 mmHg) individuals. Median plasma ANP was 27.6 pg/ml (range, 16.8-94.0 pg/ml) in the young group; 62.0 pg/ml (range, 28.6-124.3 pg/ml) in the elderly normotensive and 74.4 pg/ml (range,25.2-423.6 pg/ml) in the elderly hypertensive group. Plasma ANP rose significantly with age, but there was no difference between elderly normotensive and hypertensive groups.

Addition of candesartan to angiotensin converting enzyme inhibitor therapy in patients with chronic heart failure does not reduce levels of oxidative stress

BACKGROUND

Angiotensin II exerts a number of harmful effects in patients with chronic heart failure (CHF) and, through an increase in oxidative stress, is thought to be critical in the development of endothelial dysfunction. Angiotensin II may be elevated in CHF despite treatment with angiotensin converting enzyme (ACE) inhibitors, producing a rationale for adjunctive angiotensin receptor blockade. We investigated whether the addition of angiotensin antagonism to ACE inhibition would reduce oxidative stress and improve endothelial function and exercise tolerance in patients with chronic heart failure.

METHODS AND RESULTS

Twenty-eight heart failure patients, who were on stable ACE inhibitor therapy, were randomised to receive adjunctive therapy with candesartan or placebo. Plasma lipid-derived free radicals, TBARS and neutrophil O2-generation, markers of oxidative stress, were measured in venous blood. Arterial endothelial function was assessed as the response of the brachial artery to flow-related shear stress. Exercise capacity was determined by cardiopulmonary exercise testing. Compared with placebo, candesartan had no effect on changes in lipid derived free radicals (-0.1+/-1.2 vs. -0.1+/-1.0 units, respectively, P=NS), TBARS (-2.2+/-1.1 vs. -2.6+/-2.2 micromol/l, respectively, P=NS) or neutrophil O2-generating capacity (-7.3+/-5.1 vs. -8.4+/-7.9 mV/5x10(5) neutrophils, respectively, P=NS). There was no effect on changes in brachial artery flow-mediated dilatation (0.5+/-1.0 vs. 0.8+/-1.3%, respectively, P=NS) nor peak VO2 (1.6+/-0.7 ml/kg per min vs. 1.8+/-0.6 ml/kg per min; P=NS).

CONCLUSION

The addition of the candesartan to ACE inhibitor therapy had no effect on oxidative stress and did not improve endothelial function or exercise capacity in patients with CHF.

Plasma vasopressin and response to treatment in primary nocturnal enuresis

AIMS

To examine the relation between nocturnal vasopressin release and response to treatment with the vasopressin analogue 1-desamino-8-D-arginine vasopressin (DDAVP) in children with primary monosymptomatic nocturnal enuresis.

DESIGN

Children were recruited from a specific enuresis clinic and entered into a defined treatment programme. Nocturnal vasopressin concentrations were measured every 15 minutes over a four hour period during overnight admission.

RESULTS

Sixty seven children were eligible for entry into the study, 35 of whom agreed to overnight sampling. There was a quadratic relation between mean plasma AVP and response to treatment with DDAVP, with very high or very low concentrations being unresponsive. Plasma AVP profiles ranged from low concentrations with little variability to high concentrations with wide variability.

CONCLUSION

The ability to respond to DDAVP is related to endogenous AVP production and is influenced by neuronal patterning in early infancy. The best predictors of success with treatment were a past history of breast feeding, mean nocturnal AVP concentration, and the height of the child. The response was adversely affected by poor weight at birth and poor linear growth. The study suggests differing causes of nocturnal enuresis related to different patterns of AVP release.

Disturbance of peripheral microvascular fluid permeability by the onset of atrioventricular asynchrony in patients with programmable pacemakers

BACKGROUND

In vitro and in vivo evidence suggests that atrial natriuretic peptide can enhance fluid flux from intravascular to extravascular compartments. The relevance of this to human pathophysiology remains unclear.

OBJECTIVES

To determine whether a central haemodynamic change associated with increased plasma concentrations of atrial natriuretic peptide produces detectable change in the capillary filtration coefficient in a peripheral microvascular bed.

PATIENTS

12 patients with programmable dual chamber permanent pacemakers.

METHODS

Calf capillary filtration coefficient (using a modified plethysmographic technique) and plasma atrial natriuretic peptide concentrations were measured during atrioventricular synchronous and ventricular pacing.

RESULTS

Atrioventricular asynchrony was associated with higher mean (SD) concentrations of atrial natriuretic peptide (231.9 (123.1) v 53.5 (38.8) pg/ml) and an increased mean (SD) calf capillary filtration coefficient (4.2 (1.1) v 3.6 (1.1) ml/min.mm Hg.100 ml x 10(-3)), but there was no correlation between the magnitude of the change in these variables in individual patients.

CONCLUSIONS

The peripheral capillary filtration coefficient may change in response to altered central haemodynamics. Atrial natriuretic peptide remains one potential candidate mechanism, but other factors are also likely to be involved.

Influence of orthostatic hypotension in Parkinson's disease on plasma atrial natriuretic peptide

The effect of orthostatic hypotension in Parkinson's disease (PD) on plasma atrial natriuretic peptide (ANP) was examined in fifteen individuals with PD without autonomic dysfunction (63-85 years), nine PD patients with autonomic dysfunction (orthostatic hypotension; systolic BP change > 20 mmHg after 5 min standing: 69-82 years) and 14 fit elderly volunteers (62-93 years). The mean ANP level was 42.2 pg/ml (range 16.8-89.2 pg/ml) in the PD group without autonomic dysfunction; 44.4 pg/ml (range 27.2-91.2 pg/ml) in the PD group with autonomic dysfunction; and 48.5 pg/ml (range 22.2-111.6 pg/ml) in the elderly group. There was no statistical difference in plasma atrial natriuretic peptide between all three groups. The mean change in blood pressure was -39 mmHg (systolic) and -18 mmHg (diastolic) between supine and standing in the group with orthostatic hypotension.

An open, in-patient incremental safety and efficacy study of desmopressin in women with multiple sclerosis and nocturia

OBJECTIVES

To examine the safety and efficacy of desmopressin in three doses given to women with multiple sclerosis to treat nocturia with or without enuresis.

PATIENTS AND METHODS

Eight women with clinically confirmed multiple sclerosis and nocturia with or without enuresis were entered as in-patients into an open, nonrandomized, placebo-controlled study of incremental doses of 20, 40 and 60 micrograms desmopressin. Urinary and serum sodium, plasma arginine vasopressin and urine osmolality were monitored every 4 h for 24 h. A single dose of placebo or desmopressin was given during each of four 24-h periods.

RESULTS

There was a significant decrease in nocturnal urinary volumes and a significant increase in nocturnal urinary osmolalities in patients taking desmopressin when compared with those taking a placebo, but there was no difference among the desmopressin doses. There was no significant difference in serum sodium level between the desmopressin doses. However, at the end of the 24-h period with the 60 micrograms dose, serum sodium was decreased significantly.

CONCLUSIONS

Neither a significant decrease in nocturnal urinary volumes nor an increase in urinary osmolality was achieved by doses of desmopressin > 20 micrograms. A dose of 60 g was associated with a decreased serum sodium level at the end of the 24-h period but there was no biochemical hyponatraemia. Because there were no benefits and a possibility of clinical hyponatraemia with higher doses, doses of > 20 micrograms desmopressin cannot be recommended.

Plasma atrial natriuretic peptide levels in elderly hypertensives: effects of blood pressure reduction with amlodipine

Atrial natriuretic peptide (ANP) is a hormone of relatively recent discovery concerned with sodium homeostasis. Increased levels of ANP are found in the elderly and in hypertensives, but the mechanisms for this are unclear. This study determined the effect of amlodipine, a calcium antagonist, which is the only class of antihypertensive agent that has little or no influence on the renin-angiotensin system (Bauer and Reams, 1988) on plasma ANP in a group of 18 elderly hypertensives and a placebo (vit B complex) on a further group of 6 elderly hypertensives. The mean pre-treatment plasma ANP was 62.7 pg/ml (range 18-148.7 pg/ml) and 52.0 pg/ml (range 15.0-148.4 pg/ml) after treatment with amlodipine (not statistically significant). However, systolic blood pressure fell from a mean of 181.6 mmHg to 151.1 mmHg and diastolic blood pressure fell from a mean of 101.6 mmHg to 83.6 mmHg after treatment with amlodipine (statistically significant, P < 0.001). In the group treated with vit B complex, the mean plasma ANP level was 68.4 pg/ml (range 31.4-119.5 pg/ml) before treatment and 63.6 pg/ml (range 29.2-127.3 pg/ml) after treatment. This was not statistically significant and there was no significant change in blood pressure. These findings reinforce the theory that raised plasma ANP levels found in elderly hypertensives are a function of the aging process itself or of age-related physiological changes rather than the result of hypertension.

Reduced renal hemodynamic response to atrial natriuretic peptide in elderly volunteers

Aging is associated with decreased ability to excrete salt and water, thus increasing the susceptibility to volume overload in older individuals. Meanwhile, plasma levels of atrial natriuretic peptide (ANP) increase progressively with age for unknown reasons. We compared the natriuretic and renal hemodynamic responses to low-dose ANP infusion in an elderly group of volunteers (mean age, 74 years) with those of a group of younger subjects (mean age, 29 years). A significant reduction below baseline values in effective renal plasma flow occurred in the young group after the 2-hour peptide infusion (657 +/- 125 v 476 +/- 92 mL/min [mean +/- 1 SD]) when compared with the elderly group (two-way analysis of variance; P < 0.02). A concomitant increase in renal vascular resistance was noted in the young group only during the same period (6,631 +/- 1,384 v 9,136 +/- 2,126 dyn s cm2 x 10(6)). This increase was also significantly higher than that in the elderly group (analysis of variance; P < 0.02). Both groups demonstrated similar natriuretic responses. Absolute sodium excretion had increased significantly above baseline values in both young and elderly subjects at the end of the 2-hour peptide infusion (111 +/- 25 mumol/min to 183 +/- 33 mumol/min v 107 +/- 23 mumol/min to 198 +/- 56 mumol/min) and remained elevated until 1 hour postinfusion. We conclude that the elderly subjects in our study demonstrated a diminished renal hemodynamic response to infusion of ANP while preserving a natriuretic response similar to that found in the younger subjects.(ABSTRACT TRUNCATED AT 250 WORDS)