A Predictive Nomogram for Red Blood Cell Transfusion in Pheochromocytoma Surgery: A Study on Improving the Preoperative Management of Pheochromocytoma.

Purpose: Surgery is the major treatment option for pheochromocytoma but carries potential risks, including hemorrhage and hemodynamic instability. Even with laparoscopic adrenalectomy, intraoperative blood transfusion happens from time to time, but few studies have investigated risk factors. For the first time we develop and validate a nomogram for prediction of red blood cell transfusion in pheochromocytoma surgery. Methods: There were 246 patients in our center and 56 patients in Peking Union Medical College Hospital, who underwent pheochromocytoma surgery, enrolled in the study. We incorporated clinical and radiological risk factors, and presented this with a nomogram. Lasso regression model was used for feature selection. Logistic regression analysis was performed to identify the odd ratios. The performance of the nomogram was assessed with respect to its discrimination, calibration and clinical usefulness. Results: Thirty-two features were reduced to five, which were phenoxybenzamine use, phenoxybenzamine treatment duration, preinduction heart rate, tumor diameter and surgical procedure. The model showed good discrimination (C-index, 0.857; 95% CI, 0.781-0.836) and application in the validation sets also gave good discrimination (internal validation: C-index, 0.831; 95% CI, 0.750-0.822; external validation: C-index, 0.924; 95% CI, 0.766-1.000). Calibration tested with the Hosmer-Lemeshow test yielded a good agreement between prediction and observation (training P=0.358; internal validation P=0.205; external validation P=0.395). Odd ratios of phenoxybenzamine use, phenoxybenzamine treatment duration, preinduction HR, tumor diameter and open surgery were 13.32 (95% CI, 1.48-197.38; P = 0.034), 1.04 (95% CI, 0.99-1.08; P = 0.092), 1.04 (95% CI, 1.01-1.08; P=0.006), 1.03 (95% CI, 1.02-1.06; P<0.001), 17.13 (95% CI, 5.18-78.79; P<0.001), respectively. Decision curve analysis demonstrated the clinical usefulness of the nomogram. Conclusions: This study presents a nomogram that may be used to facilitate the prediction of red blood cell transfusion in pheochromocytoma surgery and help to do the preoperative management more efficiently.

Efficacy of α-Blockers on Hemodynamic Control during Pheochromocytoma Resection: A Randomized Controlled Trial.

CONTEXT: Pretreatment with α-adrenergic receptor blockers is recommended to prevent hemodynamic instability during resection of a pheochromocytoma or sympathetic paraganglioma (PPGL). OBJECTIVE: To determine which type of α-adrenergic receptor blocker provides the best efficacy. DESIGN: Randomized controlled open-label trial (PRESCRIPT; ClinicalTrials.gov NCT01379898). SETTING: Multicenter study including 9 centers in The Netherlands. PATIENTS: 134 patients with nonmetastatic PPGL. INTERVENTION: Phenoxybenzamine or doxazosin starting 2 to 3 weeks before surgery using a blood pressure targeted titration schedule. Intraoperative hemodynamic management was standardized. MAIN OUTCOME MEASURES: Primary efficacy endpoint was the cumulative intraoperative time outside the blood pressure target range (ie, SBP >160 mmHg or MAP <60 mmHg) expressed as a percentage of total surgical procedure time. Secondary efficacy endpoint was the value on a hemodynamic instability score. RESULTS: Median cumulative time outside blood pressure targets was 11.1% (interquartile range [IQR]: 4.3-20.6] in the phenoxybenzamine group compared to 12.2% (5.3-20.2)] in the doxazosin group (P = .75, r = 0.03). The hemodynamic instability score was 38.0 (28.8-58.0) and 50.0 (35.3-63.8) in the phenoxybenzamine and doxazosin group, respectively (P = .02, r = 0.20). The 30-day cardiovascular complication rate was 8.8% and 6.9% in the phenoxybenzamine and doxazosin group, respectively (P = .68). There was no mortality after 30 days. CONCLUSIONS: The duration of blood pressure outside the target range during resection of a PPGL was not different after preoperative treatment with either phenoxybenzamine or doxazosin. Phenoxybenzamine was more effective in preventing intraoperative hemodynamic instability, but it could not be established whether this was associated with a better clinical outcome.

Giant malignant pheochromocytoma in an elderly patient: A case report.

RATIONALE: Malignant pheochromocytoma is a rare disease and surgical resection is the only curative treatment. PATIENT CONCERNS: An 81-year-old man of Chinese ethnicity was found to have a giant retroperitoneal tumor. DIAGNOSES: B-scan ultrasonography and CT scan presented a mass above the left kidney, measuring 13.5 × 10 .6 × 9.8 cm. Subsequent analysis of 24-h urinary catecholamines and vanillylmandelic acid, as well as of blood catecholamines and blood cortisol, showed no elevated levels. INTERVENTIONS: The patient was treated with surgery. OUTCOMES: The result from immunohistochemical staining confirmed the presence of malignant pheochromocytoma. After three months follow-up, the blood pressure and serum potassium were all within normal limits, no post-operative complications, no tumor recurrence and metastasis were found. LESSONS: This is the oldest patient known to have histologic documentation of this disease. Giant malignant pheochromocytomas are rare entities requiring clinical suspicion coupled with strategic diagnostic evaluation to confirm the diagnosis, personalized therapeutic treatment is required, particularly among elderly population.

Perioperative hemodynamics and outcomes of patients on metyrosine undergoing resection of pheochromocytoma or paraganglioma.

INTRODUCTION: To describe outcomes of patients with metyrosine (MET) pretreatment for abdominal surgical resection of pheochromocytoma or paraganglioma (PCC/PGL) compared with patients who had phenoxybenzamine (PBZ) pretreatment. METHODS: Retrospective review of perioperative outcomes for PCC/PGL patients treated with MET and propensity-matched comparison of MET and PBZ (MET + PBZ) with PBZ alone. RESULTS: MET preparation was given in 63 cases (26 laparoscopic and 37 open, of which 55 also received PBZ). All patients had wide perioperative hemodynamic oscillations. Patients with open procedures required more intravenous fluids and blood transfusions; 35% required postoperative vasopressor infusions for hypotension and 38% developed acute kidney injury. One laparoscopic procedure required postoperative vasopressor infusion, and 12% of patients developed acute kidney injury. Forty-five MET + PBZ patients were propensity-matched with PBZ-only patients. Intraoperatively, MET + PBZ patients had lower minimum systolic and diastolic blood pressures than PBZ-only patients (median systolic, 74 vs 80 mm Hg, P = 0.01; median diastolic, 42 vs 46 mm Hg, P = 0.005) and larger intraoperative blood pressure oscillations (median systolic range, 112 vs 93 mm Hg, P = 0.06; median diastolic range, 58 vs 51 mm Hg, P = 0.02). Postoperative vasopressor infusion use was similar between MET + PBZ and PBZ only (16% vs 11%, P = 0.76). Major outcomes were not different between regimens. CONCLUSION: Large hemodynamic oscillations were present in our PCC/PGL patients treated with MET + PBZ. These patients had a wider range of intraoperative blood pressure variations than PBZ-only patients. No differences in postoperative comorbid outcomes were found between MET + PBZ and PBZ-only groups.

Hemodynamic Stability During Pheochromocytoma Resection: Lessons Learned Over the Last Two Decades.

BACKGROUND: Ideal perioperative management of pheochromocytomas/paragangliomas (pheo) is a subject of debate and can be highly variable. The purpose of this study was to identify potential predictive factors of hemodynamic instability during pheo resection. METHODS: A retrospective review of pheo resections from 1992 to 2013 was undertaken. Intraoperative hemodynamics, patient demographics, tumor characteristics, and perioperative management were examined. Postoperative intensive-care admission, myocardial infarction, stroke, and 30-day mortality were reviewed. Linear regression was used to analyze factors influencing intraoperative hemodynamics. RESULTS: During the 20-year study period, 100 patients underwent pheo resection. Postoperative morbidity and mortality was significantly reduced (p = 0.003) in the last 10 years of practice, and there was a trend towards greater morbidity and mortality with intraoperative hemodynamic instability (p = 0.06). The preoperative dose of phenoxybenzamine and the number of laparoscopic procedures has increased in the last decade [59 mg (95 % CI 32-108) to 106 mg (95 % CI 91-124), p = 0.008, and 27 vs. 54 %, p = 0.05, respectively]. Increased preoperative phenoxybenzamine dose was a significant predictor of improved intraoperative hemodynamic stability (p = 0.01). Lack of intraoperative magnesium use resulted in greater hemodynamic instability as preoperative systolic blood pressure increased (p = 0.002). CONCLUSIONS: Postoperative outcomes following pheo resection have improved over the last two decades. Preoperative α-blockade plays a significant role in improving intraoperative hemodynamics and post-op outcomes. Increased doses of phenoxybenzamine and utilization of laparoscopic approaches have likely contributed to improved outcomes in the last decade. Intraoperative magnesium use may provide protection against hemodynamic instability and warrants further study.

Orexin A-induced anxiety-like behavior is mediated through GABA-ergic, α- and ß-adrenergic neurotransmissions in mice.

Orexins are hypothalamic neuropeptides, which are involved in several physiological functions of the central nervous system, including anxiety and stress. Several studies provide biochemical and behavioral evidence about the anxiogenic action of orexin A. However, we have little evidence about the underlying neuromodulation. Therefore, the aim of the present study was to investigate the involvement of neurotransmitters in the orexin A-induced anxiety-like behavior in elevated plus maze (EPM) test in mice. Accordingly, mice were pretreated with a non-selective muscarinic cholinergic antagonist, atropine; a γ-aminobutyric acid subunit A (GABA-A) receptor antagonist, bicuculline; a D2, D3, D4 dopamine receptor antagonist, haloperidol; a non-specific nitric oxide synthase (NOS) inhibitor, nitro-l-arginine; a nonselective α-adrenergic receptor antagonist, phenoxybenzamine and a ß-adrenergic receptor antagonist, propranolol 30min prior to the intracerebroventricular administration of orexin A. The EPM test started 30min after the i.c.v. injection of the neuropeptide. Our results show that orexin A decreases significantly the time spent in the arms (open/open+closed) and this action is reversed by bicuculline, phenoxybenzamine and propranolol, but not by atropine, haloperidol or nitro-l-arginine. Our results provide evidence for the first time that the orexin A-induced anxiety-like behavior is mediated through GABA-A-ergic, α- and ß-adrenergic neurotransmissions, whereas muscarinic cholinergic, dopaminergic and nitrergic neurotransmissions may not be implicated.

Phenoxybenzamine is neuroprotective in a rat model of severe traumatic brain injury.

Phenoxybenzamine (PBZ) is an FDA approved α-1 adrenergic receptor antagonist that is currently used to treat symptoms of pheochromocytoma. However, it has not been studied as a neuroprotective agent for traumatic brain injury (TBI). While screening neuroprotective candidates, we found that phenoxybenzamine reduced neuronal death in rat hippocampal slice cultures following exposure to oxygen glucose deprivation (OGD). Using this system, we found that phenoxybenzamine reduced neuronal death over a broad dose range (0.1 µM-1 mM) and provided efficacy when delivered up to 16 h post-OGD. We further tested phenoxybenzamine in the rat lateral fluid percussion model of TBI. When administered 8 h after TBI, phenoxybenzamine improved neurological severity scoring and foot fault assessments. At 25 days post injury, phenoxybenzamine treated TBI animals also showed a significant improvement in both learning and memory compared to saline treated controls. We further examined gene expression changes within the cortex following TBI. At 32 h post-TBI phenoxybenzamine treated animals had significantly lower expression of pro-inflammatory signaling proteins CCL2, IL1ß, and MyD88, suggesting that phenoxybenzamine may exert a neuroprotective effect by reducing neuroinflammation after TBI. These data suggest that phenonxybenzamine may have application in the treatment of TBI.

Utility of oral nicardipine and magnesium sulfate infusion during preparation and resection of pheochromocytomas.

BACKGROUND: Calcium channel blockade with nicardipine (NC) is an alternative to phenoxybenzamine (PB) preparation for resection of a pheochromocytoma. Intraoperative magnesium sulfate infusion (+MgSO(4)) is often used for its cardiovascular stabilizing properties. We hypothesized that preparation with NC would be similar clinically to PB for resection of a pheochromocytoma, and MgSO(4) infusion would not affect intraoperative stability. METHODS: This retrospective review included 64 patients undergoing resections of a pheochromocytoma from 2003 to 2011. PB or NC was used preoperatively, with MgSO(4) use distributed equally in the population. Pre-, intra-, and postoperative hemodynamics and outcomes were compared. RESULTS: There was no difference in NC (n = 7) versus PB (n = 57) or +MgSO(4) (n = 33) versus -MgSO(4) (n = 31) groups for demographics with the exception of age. The NC group had smaller median tumor size and lesser plasma baseline levels of normetanephrine than the PB group, but subgroup analysis of all neoplasms <3.0 cm revealed no differences. Pre-, intra- and postoperative hemodynamic stability and outcomes were similar for NC versus PB analyses as well as the +MgSO(4) versus -MgSO(4) groups. CONCLUSION: NC use may be an equivalent alternative to PB in preoperative preparation, especially for smaller pheochromocytomas. Intraoperative MgSO(4) use does not seem to have a substantive effect on hemodynamic stability.

[Preoperative α-receptor block in patients with pheochromocytoma? Against]. / Präoperative α-Rezeptoren-Blockade beim Phäochromozytom? - Kontra.

Perioperative mortality regarding the resection of catecholamine-producing tumors has been markedly improved. This improvement has been attributed to the preoperative treatment with α-receptor blocking agents. An α-receptor block is still recommended prior to the resection of pheochromocytoma or paraganglioma. However, the effect has never been tested in a randomized clinical trial. Despite an assumed effective α-receptor block, many centers report systolic blood pressure increases beyond 200 mmHg. Out of 200 consecutive resections of catecholamine-producing tumors, 73 patients without an α-receptor blockade were treated. There was no significant difference in the maximum systolic blood pressure or in the incidence of hypertensive episodes. There was no correlation between the individual dose of phenoxybenzamine and the maximum blood pressure. Overall it can be concluded that with the improvement of surgical techniques, diagnostic tools and highly effective short acting substances to control hemodynamics intraoperatively, the question must be raised whether a time-consuming, unreliable pretreatment burdened with significant side effects is still required.

Antinociceptive effect of stimulating the zona incerta with glutamate in rats.

The zona incerta (ZI) is a subthalamic nucleus connected to several structures, some of them known to be involved with antinociception. The ZI itself may be involved with both antinociception and nociception. The antinociceptive effects of stimulating the ZI with glutamate using the rat tail-flick test and a rat model of incision pain were examined. The effects of intraperitoneal antagonists of acetylcholine, noradrenaline, serotonin, dopamine, or opioids on glutamate-induced antinociception from the ZI in the tail-flick test were also evaluated. The injection of glutamate (7 µg/0.25 µl) into the ZI increased tail-flick latency and inhibited post-incision pain, but did not change the animal performance in a Rota-rod test. The injection of glutamate into sites near the ZI was non effective. The glutamate-induced antinociception from the ZI did not occur in animals with bilateral lesion of the dorsolateral funiculus, or in rats treated intraperitoneally with naloxone (1 and 2 m/kg), methysergide (1 and 2 m/kg) or phenoxybenzamine (2 m/kg), but remained unchanged in rats treated with atropine, mecamylamine, or haloperidol (all given at doses of 1 and 2 m/kg). We conclude that the antinociceptive effect evoked from the ZI is not due to a reduced motor performance, is likely to result from the activation of a pain-inhibitory mechanism that descends to the spinal cord via the dorsolateral funiculus, and involves at least opioid, serotonergic and α-adrenergic mechanisms. This profile resembles the reported effects of these antagonists on the antinociception caused by stimulating the periaqueductal gray or the pedunculopontine tegmental nucleus.

Percutaneous image-guided adrenal cryoablation: procedural considerations and technical success.

PURPOSE: To assess safety, technical success, complications, and hemodynamic changes associated with the adrenal cryoablation procedure. MATERIALS AND METHODS: This retrospective review was approved by the institutional review board, with waiver of informed consent, and was compliant with the Health Insurance Portability and Accountability Act. Adult patients with adrenal metastasis who were treated with adrenal cryoablation between May 2005 and October 2009 were eligible for this review. Twelve patients (undergoing 13 procedures) with single adrenal tumors were included in the analysis. For statistical analysis, hemodynamic data were averaged for the patient undergoing the procedure twice. Technical success, safety, and local control were analyzed according to standard criteria. Hemodynamic changes during the procedure were analyzed and compared with data from an unmatched cohort of patients who underwent kidney (not in the upper pole) cryoablation (Wilcoxon rank sum test). A further subanalysis of hemodynamic changes was performed on the basis of whether preprocedural α- or ß-adrenergic blockade was used. RESULTS: With adrenal cryoablation, local control was achieved following treatment in 11 (92%; 95% confidence interval: 65.1%, 99.6%) of 12 tumors. One patient with known adrenal insufficiency underwent conservative ablation and developed ipsilateral adrenal recurrence, which was retreated. Five patients developed hypertensive crisis during the final, active thaw phase of the cryoablation procedure, and one patient developed hypertensive crisis in the immediate postablation period. Patients undergoing adrenal cryoablation experienced a significant increase in systolic blood pressure (P = .005), pulse pressure (P = .02), and mean arterial pressure (P = .01) when compared with the cohort of kidney cryoablation patients. Adrenal cryoablation patients who were not premedicated with an α-blocker (n = 5) had a higher level of systolic blood pressure increase during the cryoablation procedure when compared with their counterparts who were premedicated (n = 7) (P = .034). CONCLUSION: Adrenal cryoablation is technically feasible with a high rate of local control. Patients premedicated with the α-blocker phenoxybenzamine appear to have a reduced risk of hypertensive crisis.

Selective α1-adrenoceptor antagonist (controlled release tablets) in preoperative management of pheochromocytoma.

The objective of this article is to evaluate the efficacy of Doxazosin Mesylate Controlled Release Tablets for preoperative treatment of patients with pheochromocytoma. Between 2003 and 2008, 67 patients with confirmed diagnoses of pheochromocytoma were enrolled in this study. According to the drug used in preoperative management, patients were divided into two groups: Doxazosin Mesylate pretreatment group (n=36) and Phenoxybenzamine pretreatment group (n=31). Surgery was performed only in patients who met the optimal preoperative condition. The hematocrit decreased significantly (P<0.001) after antiadrenergic therapy in patients pretreated with phenoxybenzamine or doxazosin. There was no significant difference between the fluid intakes during operation in both groups. The systolic arterial pressures both before and after induction of anesthesia were all significantly higher in the doxazosin patients than in the phenoxybenzamine group (P<0.05). After tumor removed, the lowest systolic arterial pressure was significantly higher in doxazosin group than in phenoxybenzamine group (P<0.05). The fluctuation of systolic arterial pressure during operation was more stable in doxazosin group than in phenoxybenzamine group (P<0.05). Doxazosin mesylate controlled release tablet was as effective as phenoxybenzamine in preoperative volume expansion. Although phenoxybenzamine provided better arterial pressure control, patients pretreated with DOX experienced more stable perioperative hemodynamic changes, shorter preoperative management periods and more simple medication.

Evaluation of phenoxybenzamine in the CFA model of pain following gene expression studies and connectivity mapping.

BACKGROUND: We have previously used the rat 4 day Complete Freund's Adjuvant (CFA) model to screen compounds with potential to reduce osteoarthritic pain. The aim of this study was to identify genes altered in this model of osteoarthritic pain and use this information to infer analgesic potential of compounds based on their own gene expression profiles using the Connectivity Map approach. RESULTS: Using microarrays, we identified differentially expressed genes in L4 and L5 dorsal root ganglia (DRG) from rats that had received intraplantar CFA for 4 days compared to matched, untreated control animals. Analysis of these data indicated that the two groups were distinguishable by differences in genes important in immune responses, nerve growth and regeneration. This list of differentially expressed genes defined a "CFA signature". We used the Connectivity Map approach to identify pharmacologic agents in the Broad Institute Build02 database that had gene expression signatures that were inversely related ('negatively connected') with our CFA signature. To test the predictive nature of the Connectivity Map methodology, we tested phenoxybenzamine (an alpha adrenergic receptor antagonist) - one of the most negatively connected compounds identified in this database - for analgesic activity in the CFA model. Our results indicate that at 10 mg/kg, phenoxybenzamine demonstrated analgesia comparable to that of Naproxen in this model. CONCLUSION: Evaluation of phenoxybenzamine-induced analgesia in the current study lends support to the utility of the Connectivity Map approach for identifying compounds with analgesic properties in the CFA model.

Phaeochromocytoma in the Hong Kong Chinese population.

OBJECTIVE: To review the clinical manifestations of phaeochromocytoma in a Hong Kong Chinese population. DESIGN: Retrospective review. SETTING. Five public hospitals in Hong Kong. PATIENTS: Seventeen patients with operated phaeochromocytoma between 1994 and 2003 were reviewed retrospectively. RESULTS: Six patients (35%) were men, 11 (65%) were women. The mean age at presentation was 47 (range, 17-72) years. The diagnosis post-presentation was delayed by 1 to 132 months. Over 70% of the patients had hypertension. The most frequent symptoms were headache (53%), palpitations (53%), and sweating (41%); all these symptoms were present in 24% of the patients. Four (24%) had hereditary phaeochromocytoma/paraganglioma syndrome. The sensitivity of 24-hour urinary catecholamine measurements was 82%. Mean urinary adrenaline and noradrenaline concentrations were respectively 7- and 8-fold greater than the upper reference limits. Computed tomography and metaiodobenzylguanidine scintigraphy were the most widely used means for tumour localisation (sensitivity, 100% and 87% respectively). Approximately 65% of the patients had intra-adrenal tumours; 53% were on right side, 18% were bilateral. All the patients were prescribed phenoxybenzamine (dosage range, 20-120 mg/day) preoperatively. Two thirds of the patients had improved blood pressure 1 year after the operation. No malignancy was reported after a mean follow-up period of 7 years. CONCLUSION: Our series of patients with phaeochromocytomas commonly had a high frequency of normotension and extra-adrenal tumours. A high index of clinical suspicion and appropriate biochemical investigations are necessary to make the diagnosis, especially for patients manifesting adrenal incidentaloma and extra-adrenal lesion.

Indirect role of beta2-adrenergic receptors in the mechanism of analgesic action of nonsteroidal antiinflammatory drugs.

OBJECTIVE: Adrenal gland hormones have been shown to have a role in the antiinflammatory effect mechanism of nonsteroidal antiinflammatory drugs. This study investigates whether the analgesic effects of indomethacin, diclofenac sodium, aspirin, and nimesulide (IDAN; upper case letters of the four drugs we used) are also related to adrenal gland hormones. DESIGN: The analgesic effects of IDAN were studied in the carrageenan-induced inflammatory pain model using both intact and adrenalectomized rats. Paw withdrawal tests were performed in adrenalectomized rats that had been pretreated with phenoxybenzamine, propranolol, and metoprolol. SETTING: This study was performed in Pharmacology and Biochemistry Laboratories of Faculty of Medicine. PATIENTS/SUBJECTS: A total of 306 (114 intact and 192 adrenalectomized) male Albino Wistar rats were used. INTERVENTIONS: Adrernalectomy, drug administrations, pain model induction and pain threshold measurements were performed during the study. MEASUREMENTS AND MAIN RESULTS: Although the analgesic effects of nonsteroidal antiinflammatory drugs were lost in adrenalectomized rats, they exerted significant analgesia in adrenalectomized rats that had been pretreated with prednisolone and adrenalin. All these drugs were found to decrease serum adrenalin concentration but did not change serum cortisole (corticosterone in rats) concentration. Prednisolone and adrenalin inhibited carrageenan-induced hyperalgesia in adrenalectomized rat groups pretreated with metoprolol or phenoxybenzamine, but not in rats given propranolol. Propranolol also negated the analgesic effects of IDAN in intact rats. The analgesic effects provided by either prednisolone or adrenalin could not be inhibited by the alpha1, alpha2, or beta1 blockers but disappeared when beta2 receptors were blocked. CONCLUSIONS: The analgesic effects of nonsteroidal antiinflammatory drugs appear to be related to endogenous adrenalin and cortisole. We have demonstrated that adrenalin and prednisolone play important roles in the analgesic effect mechanism of IDAN. Prednisolone and adrenalin produce analgesic effects through beta2-adrenergic receptors, suggesting an indirect role for beta2-adrenergic receptors in the analgesic effect mechanism of the nonsteroidal antiinflammatory drugs mentioned.

Inhibition of nitric oxide-activated guanylyl cyclase by calmodulin antagonists.

BACKGROUND AND PURPOSE: Nitric oxide (NO) controls numerous physiological processes by activation of its receptor, guanylyl cyclase (sGC), leading to the accumulation of 3'-5' cyclic guanosine monophosphate (cGMP). Ca(2+)-calmodulin (CaM) regulates both NO synthesis by NO synthase and cGMP hydrolysis by phosphodiesterase-1. We report that, unexpectedly, the CaM antagonists, calmidazolium, phenoxybenzamine and trifluoperazine, also inhibited cGMP accumulation in cerebellar cells evoked by an exogenous NO donor, with IC(50) values of 11, 80 and 180 microM respectively. Here we sought to elucidate the underlying mechanism(s). EXPERIMENTAL APPROACH: We used cerebellar cell suspensions to determine the influence of CaM antagonists on all steps of the NO-cGMP pathway. Homogenized tissue and purified enzyme were used to test effects of calmidazolium on sGC activity. KEY RESULTS: Inhibition of cGMP accumulation in the cells did not depend on changes in intracellular Ca(2+) concentration. Degradation of cGMP and inactivation of NO were both inhibited by the CaM antagonists, ruling out increased loss of cGMP or NO as explanations. Instead, calmidazolium directly inhibited purified sGC (IC(50)= 10 microM). The inhibition was not in competition with NO, nor did it arise from displacement of the haem moiety from sGC. Calmidazolium decreased enzyme V(max) and K(m), indicating that it acts in an uncompetitive manner. CONCLUSIONS AND IMPLICATIONS: The disruption of every stage of NO signal transduction by common CaM antagonists, unrelated to CaM antagonism, cautions against their utility as pharmacological tools. More positively, the compounds exemplify a novel class of sGC inhibitors that, with improved selectivity, may be therapeutically valuable.