Long-term angiotensin-converting enzyme inhibitor treatment attenuates adrenergic responsiveness without altering hemodynamic control in patients undergoing cardiac surgery

BACKGROUND

The sympathoadrenal and the renin-angiotensin systems are involved in blood pressure regulation and are known to be markedly activated during cardiac surgery. Because unexpected hypotensive events have been reported repeatedly during anesthesia in patients chronically treated with angiotensin-converting enzyme (ACE) inhibitors, the authors questioned whether renin-angiotensin system blockade would alter the hemodynamic control through attenuation of the endocrine response to surgery and/or through attenuation of the pressor effects of exogenous catecholamines.

METHODS

Patients with preserved left ventricular function undergoing mitral valve replacement or coronary revascularization were divided into two groups according to preoperative drug therapy: patients receiving ACE inhibitors for at least 3 months (ACEI) group, n = 22) and those receiving other cardiovascular drug therapy (control group, n = 19). Anesthesia was induced using fentanyl and midazolam. Systemic hemodynamic variables were recorded before surgery, after anesthesia induction, during sternotomy, after aortic cross-clamping, after aortic unclamping, as well as after separation from cardiopulmonary bypass (CPB) and during skin closure. Blood was sampled repeatedly up to 24 h after surgery for hormone analysis. To test adrenergic responsiveness, incremental doses of norepinephrine were infused intravenously during hypothermic CPB and after separation from CPB. From the dose-response curves, pressor (defined as mean arterial pressure changes), and vasoconstrictor (defined as systemic vascular resistance changes) effects were analyzed, and the slopes and the dose of norepinephrine required to increase mean arterial pressure by 20% were calculated (PD(20)).

RESULTS

At no time did the systemic hemodynamics and the need for vasopressor support differ between the two treatment groups. However, for anesthesia induction, significantly less fentanyl and midazolam were given in the ACEI group. Although plasma renin activity was significantly greater in the ACEI group throughout the whole 24-h study period, plasma concentrations of angiotensin II did not differ between the two groups. Similar changes in catecholamines angiotensin II, and plasma renin activity were found in the two groups in response to surgery and CPB. The pressor and constrictor effects of norepinephrine infusion were attenuated markedly in the ACEI group: the dose-response curves were shifted to the right and the slopes were decreased at the two study periods; PD(20) was significantly greater during hypothermic CPB (0.08 micro/kg in the ACEI group vs. 0.03 micro/kg in the control group; P < 0.05) and after separation from CPB (0.52 micro/kg in the ACEI group vs. 0.1 micro/kg in the control group; P < 0.05). In both groups, PD(20) was significantly less during hypothermic CPB than in the period immediately after CPB.

CONCLUSIONS

Long-term ACE inhibitor treatment in patients with preserved left ventricular function alters neither the endocrine response nor the hemodynamic stability during cardiac surgery. However, a significantly attenuated adrenergic responsiveness associated with incomplete blockade of the plasma renin-angiotensin system supports the hypothesis that inhibition of angiotensin II generation and of bradykinin degradation within the vascular wall mediates some of the vasodilatory effects of ACE inhibitors.

Twenty-four-hour energy expenditure and urinary catecholamines of humans consuming low-to-moderate amounts of medium-chain triglycerides: a dose-response study in a human respiratory chamber

OBJECTIVE

To determine whether medium-chain triglycerides, in low-to-moderate amounts consumed with meals (at breakfast, lunch and dinner), can increase daily energy expenditure (EE) and 24-h urinary excretion of catecholamines in humans.

DESIGN

Dose-response study conducted under double-blind randomised design.

SETTING

Respiratory chamber at the Faculty of Medicine, University of Geneva.

SUBJECTS

Eight healthy young men were recruited from the student population by advertisement in our Faculty.

METHODS

24-h EE and urinary catecholamines were measured in each subject during stay in a respiratory chamber on four separate occasions. These were randomised between four different combinations of medium-chain triglycerides (MCT) and long-chain triglycerides (LCT), a total 30g/day, which was consumed with their habitual diet in three equal parts (10g each) at breakfast, lunch, and dinner in the following ratio of MCT: LCT (g/g) 0:30, 5:25, 15:15 and 30:0.

RESULTS

24-h EE increased significantly with increasing MCT:LCT ratio (ANOVA, P < 0.001), with the diet providing a total of 15-30 g MCT per day stimulating 24-h EE by 5%: this corresponds to a mean absolute increase in daily EE of approximately 500kJ, with individual values varying between 268 kJ and 756 kJ. No significant differences were observed in respiratory quotient nor in urinary nitrogen losses across diets, but 24-h urinary noradrenaline was significantly increased (ANOVA, P < 0.025), whereas adrenaline and dopamine were unaltered.

CONCLUSIONS

This study suggests that relatively low-to-moderate intake of MCT (15-30 g per day) as part of habitual diet may play a role in the control of human body composition by enhancing daily EE, and that this effect is mediated at least in part through activation of the sympathetic nervous system.

Angiotensin-II mediates norepinephrine and neuropeptide-Y secretion in a human pheochromocytoma

The potential role of angiotensin-II in mediating catecholamine and neuropeptide-Y release in a human pheochromocytoma has been investigated. Angiotensin-II type I receptors are transcribed and translated into functional proteins in a surgically removed pheochromocytoma. Primary cell culture of the tumor has been studied in a perfused system. Angiotensin-II increased the release of norepinephrine and neuropeptide-Y by the pheochromocytes. Activation of the angiotensin-II type I receptors by angiotensin-II was associated with a rise in cytosolic free calcium. The renin-angiotensin system may, therefore, contribute to the secretion of catecholamines and NPY occurring in patients with pheochromocytoma and when stimulated trigger hypertensive crisis.

The use of the rigid endoscope in trans-sphenoidal pituitary surgery

The use of the rigid endoscope has been evaluated during transsphenoidal microsurgery of 10 pituitary adenomas: three were prolactin-secreting adenomas; five growth hormone (GH)-secreting adenomas; and two without evidence of known endocrine activity. The use of the endoscope allowed close inspection and differentiation between tumour tissue and glandular remains. This resulted in microdissection of the tumour with maximum preservation of pituitary function. The angled view of the telescope helped total gross removal of tumour tissue from the less accessible supra- and para-sella extensions. More cases and a longer period of follow-up are necessary to provide long-term results.

Urinary serotonin metabolite excretion during cisplatin chemotherapy

BACKGROUND

Nausea and vomiting associated with cisplatin chemotherapy is a source of major morbidity that remains difficult to control. Acute phase (0-24 hours after induction of chemotherapy) nausea and vomiting parallels plasma serotonin release, which explains the effectiveness of 5HT3 antagonists; serotonin release in the delayed phase (24-48 hours after induction), during which consistent antiemetic control remains elusive, has not been investigated. The effect of propofol, a recent addition to the antiemetic armamentarium, on this serotonin release has not been studied.

METHODS

Ten women with nausea and vomiting refractory to ondansetron and dexamethasone prophylaxis in their first cisplatin chemotherapy cycle were studied. Serial urinary 5-hydroxyindoleacetic acid (5-HIAA) levels were determined during a 48-hour period in 30 subsequent cycles, conducted under ondansetron/dexamethasone prophylaxis together with a propofol infusion.

RESULTS

There was a significant urinary 5-HIAA peak 6 hours after induction of chemotherapy, with no peaks thereafter. Propofol did not inhibit serotonin release.

CONCLUSIONS

Cisplatin chemotherapy is associated with serotonin release in the acute phase. There is no serotonin release during the delayed phase. Thus the use of 5HT3 antagonists for delayed-phase nausea and vomiting would appear questionable.

Comparison of hyperbaric solutions of bupivacaine and tetracaine during continuous spinal anaesthesia

The aim of this study was to compare two equipotent solutions of hyperbaric bupivacaine and tetracaine in 30 elderly patients undergoing elective hip surgery under continuous spinal anaesthesia. With the patient in the supine position, 2 ml (8 mg) of either hyperbaric solution (density 1.030) were administered in a double-blind and randomized fashion. The median maximum sensory and temperature discrimination levels (T5 and T4) were similar with both solutions. The duration of analgesia was not different (114 +/- 23 min for bupivacaine and 125 +/- 35 min for tetracaine). Thirteen out of fifteen patients receiving bupivacaine and all 15 patients receiving tetracaine had complete motor blockade. The haemodynamic changes and vasopressor requirements were comparable. The plasma catecholamine levels measured at four different times remained unchanged and were not different between the two groups at any time. The authors conclude that, during continuous spinal anaesthesia, equipotent hyperbaric solutions of bupivacaine and tetracaine have similar anaesthetic and haemodynamic effects.

Cardiovascular and endocrine effects of clonidine premedication in neurosurgical patients

The present study was conducted to examine the haemodynamic and endocrine effects of clonidine, given as sole preanaesthetic medication, in neurosurgical patients. Nineteen patients of ASA physical status I and II, subjected to craniotomy, randomly received po premedication of either clonidine (300 micrograms, n = 9) or placebo (n = 10). Blood pressure and heart rate were monitored continuously, while arterial blood samples were collected at specific times, from induction of anaesthesia to recovery, for the measurement of plasma concentrations of epinephrine, norepinephrine, cortisol, aldosterone, and glucose. Clonidine treatment led to a decrease in mean arterial blood pressure (MABP), heart rate (HR), and plasma cortisol and aldosterone concentrations throughout the study, compared with placebo (P less than 0.05). Clonidine, however, did not prevent increases in MABP (16 +/- 5 mmHg, mean +/- SE, P less than 0.05) and HR (18 +/- 4 bpm, P less than 0.05) during induction of anaesthesia, which was comparable to the placebo group. Plasma catecholamine concentrations did not differ between the two groups. Plasma glucose concentrations increased in both groups at the end of the study (P less than 0.05), but were lower in clonidine-treated patients (P less than 0.05). Though statistically significant, the observed inhibitory haemodynamic and endocrine effects of clonidine seem to be of minor clinical importance. As the action of clonidine on cerebral blood flow regulation is not well known, we see no advantage in the preanaesthetic administration of clonidine to neurosurgical patients with normal cardiovascular status.

Separation of nucleotides in homogenates of octopus retina by ion-pair reversed-phase liquid chromatography and identification by mass spectrometry

An isocratic ion-pair reversed-phase liquid chromatographic method has been developed for the determination of thirteen nucleotides including cyclic AMP and cyclic GMP. The resolution capability of this method was evaluated successfully using homogenates of octopus retina, the aim being to elucidate the role of nucleotides (particularly ADP and ATP) in the control of oxidative metabolism. To overcome the inherent lack of specificity of ultraviolet detection we used the coupling of liquid chromatography with mass spectrometry, via a thermospray interface, to confirm the identity of the nucleotides of interest in the biological samples.

Purification by Immunoadsorption and Immunochemical Properties of NADP-Dependent Malic Enzymes from Leaves of C(3), C(4), and Crassulacean Acid Metabolism Plants

NADP:malic enzyme from corn (Zea mays L.) leaves was purified by conventional techniques to apparent homogeneity as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Antibodies raised against this protein in rabbits were purified, coupled covalently to protein A-Sepharose CL-4B, and used as an immunoaffinity resin to purify the NADP:malic enzymes of the C(3) plants spinach (Spinacia oleracea L.) and wheat (Triticum aestivum L.), of the Crassulacean acid metabolism (CAM) plant Bryophyllum daigremontianum R. Hamed et Perr. de la Bathie and the C(4) plants corn, sugarcane (Saccharum officinarum L.), and Portulaca grandiflora L. Such procedures yielded homogeneous protein preparations with a single protein band, as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, except for P. grandiflora L. with two bands. The specific activities of the purified proteins ranged between 56 and 91 units (milligrams per protein). NADP:malic enzyme represented up to 1% of the total soluble protein in C(4) plants, 0.5% in the CAM plant, and less than 0.01% in C(3) plants. In immunotitration tests involving immunoprecipitation and immunoinhibition of activity by an antiserum against the corn leaf enzyme, the NADP:malic enzymes of corn and sugarcane showed virtually full identity of epitopes, while the NADP:malic enzymes of the C(3) and CAM plants exhibited a cross-reaction of one-twentieth and one-fourth by these tests, respectively. The NADP:malic enzyme of P. grandiflora exhibited characteristics more closely related to the enzymes of C(3) and CAM plants than to those of C(4) plants.

Plasma concentrations of laudanosine, but not of atracurium, are increased during the anhepatic phase of orthotopic liver transplantation in pigs

To quantify the changes in plasma concentrations of atracurium and laudanosine induced by the lack of hepatic function and circulation, the authors studied nine domestic pigs (22-25 kg) undergoing an orthotopic liver transplantation, and three control animals without surgery, using atracurium as the muscle relaxant. After intubation facilitated by isoflurane 2-3%, anesthesia was maintained with isoflurane (0.5% in oxygen) and fentanyl (4 micrograms.kg-1.hr-1). Ventilation was controlled to keep end-tidal CO2 at 35-40 mmHg, body temperature maintained at 35.5-37.5 degrees C, and arterial pH at 7.35-7.50. The right sciatic nerve was stimulated with a nerve stimulator delivering a single twitch at 0.1 Hz with 0.2-ms duration, at supramaximal stimulation. The force of the corresponding evoked isometric muscle contraction was continuously measured by a force-displacement transducer. A single iv bolus of atracurium (2 mg/kg) was given to obtain a 90-95% twitch depression, followed 5 min later by a constant-rate iv infusion of atracurium at 120 micrograms.kg-1.min-1 maintained during the entire investigation. Blood samples for plasma atracurium and laudanosine concentrations were drawn every 15 min. In the control group, plasma concentrations of atracurium remained stable between 6.5-8.0 micrograms/ml following initial bolus injection; plasma concentrations of laudanosine increased during the first 60 min, then remained stable between 0.69-0.74 micrograms/ml up to the end of the study. In animals undergoing transplantation, plasma concentrations of atracurium remained stable between 10-12 micrograms/ml, despite a 90-min duration of liver exclusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Zero-order release formulation of oxprenolol hydrochloride with swelling and erosion control

Zero-order release of oxprenolol hydrochloride was obtained by controlling the swelling and erosion of the matrix. This formulation involves only mixing of drug, hydroxypropylmethylcellulose (HPMC), and sodium carboxymethylcellulose (Na CMC) at the ratio of 1:0.4:1.6, respectively, and compressing the mixture directly into tablets. The in vitro release pattern from this optimized matrix tablet was reproducible. Accelerated stability studies revealed that the optimized formulation remains stable for an approximately 2-year shelf life. This sustained-release (SR) tablet was evaluated in dogs, and for comparison a conventional (CV) formulation was also given at the same dose level. Plasma oxprenolol levels were monitored by a sensitive and specific high-performance liquid chromatographic (HPLC) method. Significant differences in the pharmacokinetic parameters, i.e., lower Cmax, higher values of tmax, MRT, AUC, and plasma concentration at 24 hr, and nearly constant plasma levels over 12 hr, indicated that the SR matrix tablet is superior to the CV rapid-releasing formulation. The in vitro release parameters and in vivo pharmacokinetics correlated well.

Glucose and carbachol generate 1,2-diacylglycerols by different mechanisms in pancreatic islets

Diacylglycerols (DAG) modulate secretory responses by the activation of protein kinase C. Early changes in DAG formation induced by the muscarinic receptor agonist carbachol were compared to those caused by the nutrient secretagogue glucose in pancreatic islets. Turnover rates of DAG were investigated in radiolabeling experiments, whereas changes in total mass and fatty acid composition of DAG were assessed by gas-liquid chromatography. When islet lipids were labeled to steady state in tissue culture with [3H]glycerol, carbachol induced a rapid (10 s) and sustained increase of [3H]DAG generation. In contrast, glucose stimulation failed to increase [3H]glycerol containing DAG, and this was probably due to the isotopic dilution of the label secondary to enhanced glycolysis. This was substantiated by following the transfer of 14C from glucose into DAG. Within 1 min of acute exposure of islets to D-[U-14C]-glucose at stimulatory concentrations, DAG labeling increased fivefold representing up to 2% of total glucose usage. Similar stimulation of 14C incorporation into other neutral lipids and inositol phospholipids was observed, suggesting the enhanced de novo synthesis of phosphatidic acid, the common precursor for DAG, and inositol phospholipids from glycolytic intermediates. Transfer of 14C from glucose was not stimulated by agents such as carbachol and exogenous phospholipase C that act primarily on inositol phospholipid breakdown. The total mass of islet DAG was increased by 60% after both carbachol and glucose stimulation. However, analysis of the fatty acid composition of carbachol-generated DAG revealed at the early time point (10 s) a prevalent stearoyl-arachidonoyl configuration similar to that reported for inositol phospholipids. This pattern shifted to a DAG enriched in palmitic acid at a later time point. Glucose-stimulated islets displayed a predominance of palmitic acid containing DAG, indicating increased de novo synthesis of the putative second messenger rather than its formation by inositol phospholipid hydrolysis. Indeed, steady-state labeling of these phospholipids with [3H]inositol confirmed this idea since only carbachol caused detectable inositol phospholipid hydrolysis. Thus, although protein kinase C may be activated by both carbachol and glucose, the two secretagogues generate diacylglycerols through different mechanisms.

Calcium-channel inhibition in pheochromocytoma

Nifedipine, a calcium-antagonist and potent vasodilator, was tested in three patients with pheochromocytoma. In two patients who were normotensive, nifedipine prevented a rise in blood pressure but not in plasma epinephrine and norepinephrine following the iv injection of the dopamine-antagonist metoclopramide. In another patient who was hypertensive, nifedipine was as effective in lowering blood pressure as labetalol or phenoxybenzamine, and did not modify the elevated plasma and urinary catecholamines. Nifedipine appears to control hypertension in pheochromocytoma, without altering catecholamine levels, suggesting that calcium-channel blockade interferes with catecholamine vascular action but not with tumoural catecholamine release. Calcium-antagonists may be helpful in preventing the pressor complications of provocative tests used in the screening of pheochromocytoma.

[Diagnosis of myocardial infarct by means of a quick determination of the MB fraction of serum creatinephosphokinase]

A rapid method of determining creatine phosphokinase (CPK) isoenzymes using dithiothreitol, a reducing agent which activates the main fractions of the CPK molecule (MM and MB), was assessed in 68 subjects (34 with myocardial infarction, 18 with skeletal muscle lesions, 16 normal). In acute myocardial infarction, the mean peak of CPK-MB in serum increases to 13.3% of the total CPK (range 8.8% to 21%) from the 18th to the 24th hour after onset of symptoms, whereas in skeletal muscle lesions CPK-MB reaches only 1% of total CPK (range 0% to 2.9%), and in normal subjects CPK-MB is absent. This highly significant difference (p less than 0.001) makes it possible to distinguish accurately between myocardial infarction and skeletal muscle lesions (trauma, hematoma, myositis, hypothyroidism). By its sensitivity (100%) and specificity (97%) this rapid and inexpensive method finds its optimal sphere of application in emergency wards and coronary care units.