Anesth Analg 2003;97:1501-1503
© 2003 International Anesthesia Research Society
NEUROSURGICAL ANESTHESIA
A Comparison of Cerebrospinal Fluid and Plasma Urotensin II Concentrations in Normotensive and Hypertensive Patients Undergoing Urological Surgery During Spinal Anesthesia: A Pilot Study
Jonathan P. Thompson, MD FRCA,
Philip Watt, FRCA,
Sunita Sanghavi, FRCA,
James W. Strupish, BSc, and
David G. Lambert, PhD
University Department of Anaesthesia, Critical Care and Pain Management, Leicester Royal Infirmary, Leicester, United Kingdom
Address correspondence and reprint requests to D. G. Lambert, PhD, University Department of Anaesthesia, Critical Care and Pain Management, Leicester Royal Infirmary, Leicester, LE1 5WW, UK. Address e-mail to DGL3{at}le.ac.uk
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Abstract
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Urotensin II is a novel endogenous vasoconstrictor. There are no data describing cerebrospinal fluid (CSF) concentrations in humans. Therefore, in this study, we aimed to quantify and compare plasma and CSF urotensin II concentrations in patients with essential hypertension and matched controls. Twenty male patients (10 receiving >6 mo of treatment for essential hypertension and 10 normotensive controls scheduled to undergo urological surgery under spinal anesthesia) were recruited into this single-blinded cohort study. Plasma and CSF urotensin II concentrations were measured by radioimmunoassay, along with mean arterial blood pressure (MAP), before admission, on the day of admission, and immediately before anesthesia. CSF and plasma urotensin II concentrations were low. Median (range) values in CSF for all 20 patients were significantly lower than plasma by 
15% (19.0 pg/mL [10.6–24.9 pg/mL] compared with 22.3 pg/mL [17.7–28.4 pg/mL]; P = 0.004). There were no significant differences between normotensive and hypertensive patients in either CSF or plasma concentrations. However, there was a significant positive correlation between average MAP and CSF urotensin II concentrations (r2 = 0.44; P = 0.036) in the hypertensive group.
IMPLICATIONS: Urotensin II is the most potent known endogenous human vasoconstrictor. In this pilot study, we report for the first time that cerebrospinal fluid levels are smaller than plasma levels and that there may be some association with increased blood pressure.
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Introduction
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Urotensin II is the most potent known endogenous human vasoconstrictor, typically displaying more than one order of magnitude higher in vitro potency than endothelin-1 (1) (see Ref. 2 for review). This undecapeptide (Glu-Thr-Pro-Asp-[Cys-Phe-Trp-Lys-Tyr-Cys]-Val) is the endogenous ligand for the orphan G-protein-coupled receptor GPR14, and both peptide and receptor have been identified in human vasculature, where they produce arterial and venous constriction (2). In addition, both peptide and receptor are located in the brain (2). To detail a role for urotensin II in the pathophysiology of human disease and design novel ligands (especially antagonists) for therapeutic use, information on circulating and cerebrospinal fluid (CSF) peptide concentrations in a number of disease states is required. While the direct anesthetic relevance of this system remains to be defined, it is not inconceivable that synthetic urotensin receptor ligands may eventually be used to control hypo- or hypertensive episodes in the intensive care setting. There are no data describing CSF concentrations in humans. Therefore, in this study, we aimed to quantify and compare plasma and CSF urotensin II concentrations in patients with essential hypertension and matched controls.
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Methods
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With local research ethics committee approval and written, informed consent, 10 patients receiving long-term (>6 mo) treatment for essential hypertension and 10 normotensive patients were recruited into this single-blinded cohort study. All were scheduled to undergo urological surgery under spinal anesthesia (transurethral resection of prostate or bladder tumor). Exclusion criteria were secondary hypertension, abnormal renal function (serum creatinine >120 mmol/L), urgent or emergency surgery, general anesthesia, sedative or opioid analgesic medication within 24 h, and patients in control groups receiving vasoactive medication for other indications. Mean arterial blood pressure (MAP) was measured at a preoperative assessment clinic, at hospital admission, and in the anesthetic room immediately before anesthesia. Here an indwelling venous cannula was inserted, and 5 mL of whole blood was collected into EDTA monovette containers containing 3 trypsin-inhibitory units of aprotinin and maintained on ice. These samples were centrifuged at 1500g for 15 min at 4°C, 1 mL of plasma was removed, and 1 mL of 1% (vol/vol) trifluoroacetic acid (TFA) was added. During spinal anesthesia, drops of CSF were collected (total of 
1 mL), 1 mL was dispensed into a 5-mL polypropylene tube, and 1 mL of 1% TFA was immediately added. All samples were then frozen and stored at -20°C until extraction and assayed as a single batch. After sample collection, anesthesia and surgery continued.
Two-milliliter samples (1:1 sample/TFA) were thawed and centrifuged at 12,000g for 15 min at 4°C, and the supernatant was loaded (0.3 mL/min) onto equilibrated (2 mL of 60% acetonitrile in 1% TFA, followed by three 3-mL washes with 1% TFA at a flow rate of 1 mL/min) Strata C18 solid-phase extraction cartridges (Phenomenex, Macclesfield, UK). The column was then washed twice with 3 mL of 1% TFA at a flow rate 1 mL/min. Finally, urotensin II was eluted with 2.5 mL of 60% acetonitrile in 1% TFA and evaporated to dryness in a centrifugal evaporator. Before assay, the sample was reconstituted in 0.25 mL of radioimmunoassay buffer. Using this procedure with "spiked samples," we estimate our peptide recovery at 100% with negligible (<1 pg per tube; see below) concentrations in plasma free extracted TFA. Urotensin II was measured by using a commercial radioimmunoassay kit (Phoenix Europe GmbH, Karlsruhe, Germany) as a single batch, according to the manufacturer’s instructions. This assay has a range of 1–128 pg per tube and no cross-reactivity with endothelin-1 or angiotensin II. The intraassay coefficient of variation for this assay was 7.5% on the basis of five midrange samples (32 pg per tube).
Urotensin data are presented as median (range), and between-group comparisons were made with Mann-Whitney (unpaired) or Wilcoxon’s signed rank tests (paired), as appropriate. This is the first study to measure CSF urotensin II concentrations, so power calculations were based on plasma concentrations. Totsune et al. (3) reported mean (SD) plasma urotensin II concentrations of 4.4 fmol/mL (1.0 fmol/mL) in healthy volunteers. Extrapolation from these data suggested that 10 patients per group would detect a 50% difference between normotensive and hypertensive patients (
= 0.05; ß = 0.2).
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Results
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There were no significant differences between the groups with respect to age or MAP measured at preadmission or immediately before anesthesia. All patients were male. The mean duration of antihypertensive therapy was 4.3 yr (range, 1–8 yr). There was a small but statistically significant difference between groups in MAP at hospital admission, but these data mostly confirm the efficacy of antihypertensive medication (Table 1). CSF and plasma urotensin II concentrations were low. Median (range) values in CSF for all 20 patients were significantly lower than plasma by 15% (19.0 pg/mL [10.6–24.9 pg/mL] compared with 22.3 pg/mL [17.7–28.4 pg/mL]; P = 0.004). There was a weak but statistically significant decline in CSF concentrations with increasing age (from 55 to 89 yr; r2 = 0.26; P = 0.021) for all 20 patients. There were no significant between-group differences in either CSF or plasma concentrations (Fig. 1A). However, there was a significant positive correlation between average MAP and CSF urotensin II concentrations (r2 = 0.44; P = 0.036) in the hypertensive group.
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Figure 1. A, Comparison of cerebrospinal fluid (CSF) and plasma urotensin II concentrations in normotensive (N) and hypertensive (H) patients. Data are median, interquartile range, and minimum/maximum values. CSF urotensin II concentrations were significantly lower than plasma. B, Significant positive correlation between CSF urotensin II concentrations and average mean arterial blood pressure (MAP) in the hypertensive group.
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Discussion
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We have compared CSF and plasma urotensin II concentrations in normotensive and hypertensive patients undergoing transurethral procedures under spinal anesthesia. In this small pilot study, we report for the first time that CSF urotensin II concentrations are approximately 15% lower than paired plasma samples. In addition, urotensin II is, in general, not well correlated with MAP (although there was a significant positive correlation with average MAP in the hypertensive group). Moreover, urotensin II concentrations are not increased in a hypertensive group relative to normotensive control patients.
There have been several studies detailing plasma (but not CSF) urotensin II concentrations that indicated wide variations and apparently conflicting values. Totsune et al. (4) reported values of 6 pg/mL, which are increased two- to threefold in renal failure (3) and less than twofold in insulin-dependent diabetes mellitus. In patients with cirrhosis and portal hypertension, urotensin II was also increased (12.3 ng/mL compared with 3.6 ng/mL in controls) (5). These values are 161-fold higher than our control normotensive population and 590-fold higher than those of Totsune et al. (3,4). In three studies of plasma concentrations in heart failure, control values have varied from 1.41 to approximately 100 pg/mL, with 2 studies reporting an increase (6,7) and one reporting no change (8). The positive correlation observed between CSF urotensin II concentrations and average MAP is interesting, although Heller et al. (5) reported a negative correlation between plasma urotensin II and MAP in cirrhotics. Although normotensive, our control patients were elderly, and several had coexisting disease.
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Acknowledgments
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Funded by University Hospitals of Leicester NHS Trust.
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References
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- Douglas SA, Ohlstein EH. Human urotensin-II, the most potent mammalian vasoconstrictor identified to date, as a therapeutic target for the management of cardiovascular disease. Trends Cardiovasc Med 2000; 10: 229–37.[ISI][Medline]
- Totsune K, Takahashi K, Arihara Z, et al. Role of urotensin II in patients on dialysis. Lancet 2001; 358: 810–1.[ISI][Medline]
- Totsune K, Takahashi K, Arihara Z, et al. Increased plasma urotensin II levels in patients with diabetes mellitus. Clin Sci 2003; 104: 1–5.[Medline]
- Heller J, Schepke M, Neef M, et al. Increased urotensin II plasma levels in patients with cirrhosis and portal hypertension. J Hepatol 2002; 37: 767–72.[ISI][Medline]
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- Dschietzig T, Bartsch C, Pregla R, et al. Plasma levels and cardiovascular gene expression of urotensin-II in human heart failure. Regul Pept 2002; 110: 33–8.[ISI][Medline]
Accepted for publication June 25, 2003.
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Abstract
Introduction
