Sympathoexcitatory response to cyclosporin A and baroreflex resetting

Sinus bradycardia as a rare adverse event in patients receiving cyclosporine A after allogeneic hematopoietic stem cell transplantation

Cyclosporine A (CSA) is a commonly used immunosuppressive agent for the prophylaxis of graft-versus-host disease following allogeneic hematopoietic stem cell transplantation (alloHSCT). While tachycardia is a known adverse effect of CSA, bradycardia remains a phenomenon rarely described in the literature. We conducted a retrospective evaluation of the incidence of bradycardia in patients after alloHSCT treated with CSA between January 2020 and February 2023 at our center. Out of 206 patients, sinus bradycardia following the administration of CSA was observed in 6 (2.9%), comprising 3 women and 3 men, with the median age of 55 years (range: 20-65). The underlying diseases were myeloid malignancies in 4 and aggressive lymphoma in 2 patients. The patients received grafts from a matched unrelated (n=5) or a haploidentical family donor (n=1) following various conditioning regimens. Coexisting cardiovascular disorders were found in 5 of the 6 patients. All patients experienced symptomatic bradycardia within 1-4 days (median 2 days) after CSA introduction, which persisted until CSA withdrawal. One patient required treatment with atropine. All patients continued their immunosuppressive therapy with tacrolimus, which was well-tolerated Our study indicates CSA as a causative factor of sinus bradycardia in a small percentage of alloHSCT patients receiving CSA as graft-versus host disease (GvHD) prophylaxis. Importantly, these patients did not experience any cardiac complications when switched to tacrolimus. Although further research on the effects of CSA on heart automatation is needed, our single-center experience can help prompt diagnosis and therapeutic intervention in daily clinical practice.

Calcineurin Controls Hypothalamic NMDA Receptor Activity and Sympathetic Outflow

Rationale:

Hypertension is a common and serious adverse effect of calcineurin inhibitors, including cyclosporine and tacrolimus (FK506). Although increased sympathetic nerve discharges are associated with calcineurin inhibitor–induced hypertension, the sources of excess sympathetic outflow and underlying mechanisms remain elusive. Calcineurin (protein phosphatase-2B) is broadly expressed in the brain, including the paraventricular nuclear (PVN) of the hypothalamus, which is critically involved in regulating sympathetic vasomotor tone.

Objective:

We determined whether prolonged treatment with the calcineurin inhibitor causes elevated sympathetic output and persistent hypertension by potentiating synaptic N-methyl-D-aspartate (NMDA) receptor activity in the PVN.

Methods and Results:

Telemetry recordings showed that systemic administration of FK506 (3 mg/kg per day) for 14 days caused a gradual and profound increase in arterial blood pressure in rats, which lasted at least 7 days after discontinuing FK506 treatment. Correspondingly, systemic treatment with FK506 markedly reduced calcineurin activity in the PVN and circumventricular organs, but not rostral ventrolateral medulla, and increased the phosphorylation level and synaptic trafficking of NMDA receptors in the PVN. Immunocytochemistry labeling showed that calcineurin was expressed in presympathetic neurons in the PVN. Whole-cell patch-clamp recordings in brain slices revealed that treatment with FK506 increased baseline firing activity of PVN presympathetic neurons; this increase was blocked by the NMDA or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor antagonist. Also, treatment with FK506 markedly increased presynaptic and postsynaptic NMDA receptor activity of PVN presympathetic neurons. Furthermore, microinjection of the NMDA or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor antagonist into the PVN of anesthetized rats preferentially attenuated renal sympathetic nerve discharges and blood pressure elevated by FK506 treatment. In addition, systemic administration of memantine, a clinically used NMDA receptor antagonist, effectively attenuated FK506 treatment–induced hypertension in conscious rats.

Conclusions:

Our findings reveal that normal calcineurin activity in the PVN constitutively restricts sympathetic vasomotor tone via suppressing NMDA receptor activity, which may be targeted for treating calcineurin inhibitor–induced hypertension.

Renal transplantation normalizes baroreflex sensitivity through improvement in central arterial stiffness

BACKGROUND

In end-stage renal disease (ESRD) patients, the most common cause of mortality and morbidity are cardiovascular events. This could be attributed to the impaired baroreflex function observed in this group of patients. The effect of renal transplantation (RT) on the baroreflex sensitivity (BRS) in ESRD patients has been inadequately addressed. Therefore, we investigated baroreflex function and its relation to arterial stiffness indices and cardiovascular variability parameters (heart rate and blood pressure variability--HRV and BPV) in ESRD patients before and after transplantation to decipher the underlying mechanism of attenuated BRS in ESRD patients.

METHODS

We studied 23 ESRD patients (mean age; 36 years) prospectively before and at 3 and 6 months after RT. Baroreflex function was determined by spontaneous method (sequence and spectral indices). Short-term HRV and BPV were assessed using power spectrum analysis of RR intervals and systolic blood pressure by frequency domain analysis. Arterial stiffness indices were assessed by carotid-femoral pulse-wave velocity (PWV), augmentation index (AI) and central pulse pressure using Sphygmocor Vx device (AtCor Medical, Australia).

RESULTS

RT was associated with the normalization of BRS by 6 months. Arterial stiffness indices, such as AI and central pulse pressure, showed a significant reduction as early as 3 months after RT. PWV and frequency domain measures of HRV after RT did not show statistically significant changes except the LF/HF ratio which had a significant increase at 6 months when compared with baseline. Systolic BPV total power showed a significant reduction by 3 months after RT.

CONCLUSIONS

Our data suggest that RT normalizes BRS in ESRD patients by 6 months which follows the improvement in the AI and central pulse pressure.

Crosstalk between central pathways of nitric oxide and carbon monoxide in the hypertensive action of cyclosporine

Although the intermediary role of central neurons in the hypertensive and sympathoexcitatory actions of cyclosporine (CSA) has been recognized in previous studies including our own, the underlying mechanism remains obscure. In this study, we tested the hypothesis that central pathways of nitric oxide (NO) and carbon monoxide (CO) modulate the blood pressure (BP) response elicited by CSA in conscious rats. Hemodynamic effects of CSA were evaluated in absence and presence of maneuvers that inhibit or facilitate biosynthesizing enzymes of NO (NOS) or CO (heme oxygenase, HO). CSA (20mg/kg i.v.) produced abrupt increases in BP that peaked in 5min and maintained for at least 45min. The hypertensive effect of CSA disappeared in rats pretreated intracisternally (i.c.) with N(ω)-nitro-l-arginine methyl ester (L-NAME, nonselective NOS inhibitor), N(5)-(1-iminoethyl)-l-ornithine (L-NIO, selective eNOS inhibitor), N(ω)-propyl-l-arginine (NPLA, selective nNOS inhibitor), or 1H-[1,2,4] oxadiazolo[4,3-a] quinoxalin-1-one (ODQ, guanylate cyclase inhibitor), suggesting the importance of central eNOS/nNOS/GC cascade in CSA-induced hypertension. L-NAME also abolished the hypotension caused by the sympatholytic drug moxonidine, indicating a tonic sympathoinhibitory action for NO. The inhibition of HO activity by zinc protoporphyrin IX (ZnPP) abrogated the hypertensive action of CSA. The abolition by L-NAME or ZnPP of CSA hypertension was compromised upon simultaneous i.c. exposure to hemin (HO substrate) and l-arginine (NOS substrate), respectively. Together, the interruption of the mutually facilitated NOS/NO and HO/CO pathways and coupled GC/cGMP in central neuronal pools accounts, at least partly, for the hypertensive and perhaps sympathoexcitatory actions of CSA.

Determinants of baroreflex function in juvenile end-stage renal disease

Arterial baroreflex sensitivity (BRS) is markedly reduced in middle-aged patients with end-stage renal disease (ESRD), due to the combined effects of aging, arterial stiffening, and autonomic neuropathy. Much less is known about the effects of ESRD on arterial baroreflex in juvenile patients. Therefore, we investigated baroreflex function and its relation to carotid artery elasticity and heart rate variability in children and young adults with ESRD. We studied 42 subjects (9-30 years): 14 patients on maintenance hemodialysis (HD), 14 renal transplant recipients (RT), and 14 healthy control subjects (C). Baroreflex function was determined by pharmacological (BRS) and spontaneous (sequence and spectral indices) techniques. Carotid artery elasticity was characterized by stiffness index beta. Heart rate variability was assessed using time and frequency domain measures. Data are expressed as mean+/-s.d. BRS was markedly reduced in HD as compared to C (10.0+/-4.2 vs 25.7+/-5.9 ms/mm Hg); spontaneous indices were reduced to similar extent. Carotid artery stiffness was approximately 50% higher in HD than in C and was inversely related to BRS. Heart rate variability was also compromised in HD, and was directly related to spontaneous indices. No significant differences existed in any of these variables between RT and C. Decreased baroreflex function in juvenile HD is partly due to loss of carotid artery elasticity and partly due to impaired heart rate variability. Renal transplantation may partly prevent impairment or improve compromised baroreflex function in young patients with ESRD.

Spontaneous baroreflex cardiac sensitivity in end-stage liver disease: effect of liver transplantation

BACKGROUND AND OBJECTIVE

End-stage liver disease is associated with an imbalance in the autonomic nervous system. The purpose of this study was to estimate the effect of liver transplantation on this imbalance.

METHOD

The study involved 10 patients undergoing liver transplantation and 9 patients without liver impairment undergoing liver surgery. The spontaneous baroreflex sensitivity was measured before and 1 month after surgery for the liver surgery group; before and 1, 3, 6, 12 and 18 months after orthotopic liver transplantation.

RESULTS

The spontaneous baroreflex slope of patients with end-stage liver disease was decreased before liver transplantation compared to the liver surgery group (3.9 +/- 2.5 ms mmHg(-1) vs. 9.9 +/- 5.0 ms mmHg(-1), P = 0.002). The mean slope was significantly increased at 12 and 18 months compared to the pre-transplantation value (3.9 +/- 2.5 ms mmHg(-1) vs. 8.1 +/- 6.6 ms mmHg(-1) and 7.4 +/- 4.8 ms mmHg(-1), respectively; P = 0.042). Nevertheless, further analysis of individual data showed that only four patients exhibited a marked increase in their baroreflex slope 12 months after the liver transplantation whereas it remained decreased in the six others.

CONCLUSIONS

These results confirm that the baroreflex sensitivity is depressed in end-stage liver disease in line with an autonomic nervous system imbalance. The liver transplantation reverses this disturbance only in some patients.

Time-Domain Evaluation of Cyclosporine Interaction with Hemodynamic Variability in Rats

This study investigated the effects of chronic exposure of Wistar rats to the immunosuppressant drug cyclosporine on blood pressure, heart rate, and their variability and the role of sympathovagal balance in this interaction. The blood pressure variability was determined as the standard deviation of the mean arterial pressure (SDMAP). Two time-domain heart rate variability indices were employed, the standard deviation of beat-to-beat intervals (SDRR) and the root mean square of successive beat-to-beat differences in R-R interval durations (rMSSD). Subcutaneous cyclosporine administration (20 mg/kg/day) for 12 days had no effect on blood pressure or its variability index (SDMAP). In contrast, the average level of heart rate and its variability indices (SDRR and rMSSD) showed significant increases and decreases, respectively, in cyclosporine- compared with vehicle-treated rats. Vagal (atropine) or beta -adrenergic (propranolol) blockade had no effect on blood pressure but elicited increases and decreases, respectively, in heart rate. Compared with control rats, cyclosporine-treated rats exhibited lesser tachycardic responses to atropine and greater bradycardic responses to propranolol, suggesting alterations of cardiac vagal (attenuation) and sympathetic (enhancement) activity by cyclosporine. Further, atropine reduced indices of heart rate variability (rMSSD and SDRR) in control rats, effects that were blunted by cyclosporine treatment. On the other hand, propranolol had no effect on heart rate variability in either cyclosporine-treated or control rats. These findings implicate vagally-mediated alterations in the cardiac sympathovagal balance in the cyclosporine-induced impairment of heart rate oscillations.

Role of angiotensin II and reactive oxygen species in cyclosporine A-dependent hypertension

Treatment with cyclosporine A (CysA), a potent immunosuppressive agent, is associated with systemic and renal vasoconstriction, leading to hypertension. The present study was conducted to elucidate the contribution of angiotensin II (Ang II) to CysA-induced hypertension and reactive oxygen species (ROS) generation. CysA (30 mg/kg per day SC), given for 3 weeks in rats, increased systolic blood pressure (SBP) from 119+/-2 to 145+/-3 mm Hg (n=7). Plasma and kidney Ang II levels were significantly higher in CysA-treated rats (136+/-10 fmol/mL and 516+/-70 fmol/g) than in vehicle-treated (1 mL olive oil) rats (76+/-10 fmol/mL and 222+/-21 fmol/g, n=7). CysA treatment increased AT1 receptor protein expression in the aorta (by 251+/-35%), whereas it was reduced in the kidney (by -32+/-4%). Superoxide anion production in aortic segments and kidney thiobarbituric acid-reactive substance (TBARS) contents were higher in CysA-treated rats (26+/-2 counts/min per milligram and 37+/-3 nmol/g) than in vehicle-treated rats (17+/-1 counts/min per milligram and 24+/-3 nmol/g). Concurrent administration of an AT1 receptor antagonist, valsartan (30 mg/kg per day, in drinking water), to CysA-treated rats (n=7) significantly decreased SBP (113+/-4 mm Hg) and prevented increases in vascular superoxide (16+/-2 counts/min per milligram) and kidney TBARS contents (21+/-3 nmol/g). Similarly, treatment with a superoxide dismutase mimetic, 4-hydroxy-2,2,6,6,-tetramethylpiperidine-N-oxyl (Tempol; 3 mmol/L in drinking water, n=7), prevented CysA-induced increases in SBP (115+/-3 mm Hg), vascular superoxide (16+/-1 counts/min per milligram), and kidney TBARS contents (19+/-2 nmol/g). These data suggest that ROS generation induced by augmented Ang II levels contributes to the development of CysA-induced hypertension.

Cyclosporine induces progressive attenuation of baroreceptor heart rate response and cumulative pressor response in conscious unrestrained rats

Cyclosporine A (CsA) use is associated with hypertension and reduced baroreceptor sensitivity (BRS), but the underlying mechanisms remain unresolved. In this study, we investigated whether CsA attenuation of BRS is 1) dependent on treatment regimen, and 2) causative of the pressor response. Furthermore, we investigated whether a reduction in plasma testosterone contributes to BRS attenuation caused by short-term CsA administration. The effects of the clinically used CsA formulation (15 mg/kg/day i.v. for 5 days) on mean arterial pressure (MAP), heart rate, BRS, and body weight were investigated in conscious rats. CsA caused reproducible pressor responses (15.1 +/- 3.0 mm Hg) starting after the first dose and continuing through the 5 days of the study. BRS and baseline MAP were inversely related in the CsA group because of a progressive reduction in BRS, which started on day 2 and reached approximately 50% of baseline on day 5 and a cumulative elevation in MAP. The inverse BRS and MAP responses required daily administration of CsA because neither response was evident throughout the 5-day observation period after a single dose of CsA. Plasma testosterone levels were similar in all groups, whereas the body weight decreased approximately 10% in the CsA group on day 5. These findings suggest 1) CsA attenuation of BRS is relatively rapid and cumulative; 2) the attenuation of BRS may contribute to the delayed, but not to the acute, pressor elicited by CsA; and 3) the cumulative reduction in BRS caused by short-term (5-day) CsA treatment is not testosterone-related.

Cyclosporine attenuates the autonomic modulation of reflex chronotropic responses in conscious rats

Cyclosporine A (CyA), an immunosuppressant drug, has been shown to attenuate the baroreflex control of heart rate (HR). This study investigated whether or not the CyA-induced baroreflex dysfunction is due to alterations in the autonomic (sympathetic and parasympathetic) control of the heart. We evaluated the effect of muscarinic or beta-adrenergic blockade by atropine and propranolol, respectively, on reflex HR responses in conscious rats treated with CyA (20 mg·kg–1·day–1 dissolved in sesame oil) for 11–13 days or the vehicle. Baroreflex curves relating changes in HR to increases or decreases in blood pressure (BP) evoked by phenylephrine (PE) and sodium nitroprusside (NP), respectively, were constructed and the slopes of the curves were taken as a measure of baroreflex sensitivity (BRSPE and BRSNP). Intravenous administration of PE and NP produced dose-related increases and decreases in BP, respectively, that were associated with reciprocal changes in HR. CyA caused significant (P < 0.05) reductions in reflex HR responses as indicated by the smaller BRSPE (–0.97 ± 0.07 versus –1.47 ± 0.10 beats·min–1·mmHg–1 (1 mmHg = 133.322 Pa)) and BRSNP (–2.49 ± 0.29 versus –5.23 ± 0.42 beats·min–1·mmHg–1) in CyA-treated versus control rats. Vagal withdrawal evoked by muscarinic blockade elicited significantly lesser attenuation of BRSPE in CyA compared with control rats (40.2 ± 8.0 versus 57.7 ± 4.4%) and abolished the BRSPE difference between the two groups, suggesting that CyA reduces vagal activity. CyA also appears to impair cardiac sympathetic control because blockade of beta-adrenergic receptors by propranolol was less effective in reducing reflex tachycardic responses in CyA compared with control rats (41.6 ± 4.2 versus 59.5 ± 4.5%). These findings confirm earlier reports that CyA attenuates the baroreceptor control of HR. More importantly, the study provides the first pharmacological evidence that CyA atten uates reflex chronotropic responses via impairment of the autonomic modulation of the baroreceptor neural pathways.Key words: cyclosporine A, baroreflex sensitivity, autonomic control, atropine, propranolol.

Cyclosporine adversely affects baroreflexes via inhibition of testosterone modulation of cardiac vagal control

Previous studies have shown that the immunosuppressant drug cyclosporine A attenuates arterial baroreceptor function. This study investigated whether the modulatory effect of cyclosporine on baroreceptor function involves inhibition of the baroreflex-facilitatory effect of testosterone. The role of cardiac autonomic control in cyclosporine-testosterone baroreflex interaction was also investigated. Baroreflex curves relating bradycardic responses to increments in blood pressure evoked by phenylephrine were constructed in conscious, sham-operated, castrated rats and in testosterone-replaced castrated (CAS + T) rats in the absence and presence of cyclosporine. The slopes of the curves were taken as an index of the baroreflex sensitivity (BRS). Short-term (11-13 days) cyclosporine treatment or castration reduced plasma testosterone levels and caused similar attenuation of the reflex bradycardia, as indicated by the significantly smaller BRS compared with sham-operated values (-0.97 +/- 0.07, -0.86 +/- 0.06, and -1.47 +/- 0.10 beats/min/mm Hg, respectively). The notion that androgens facilitate baroreflexes is further confirmed by the observation that testosterone replacement of castrated rats restored plasma testosterone and BRS to sham-operated levels. Cyclosporine had no effect on BRS in castrated rats but caused a significant reduction in CAS + T rats. Muscarinic blockade by atropine caused approximately 60% reduction in the BRS in sham-operated rats, an effect that was significantly and similarly diminished by castration, cyclosporine, or their combination. beta-Adrenergic blockade by propranolol caused no significant changes in BRS. These findings suggest that cyclosporine attenuates baroreflex responsiveness via, at least partly, inhibition of the testosterone-induced facilitation of cardiomotor vagal control.

Cyclosporin: an updated review of the pharmacokinetic properties, clinical efficacy and tolerability of a microemulsion-based formulation (neoral)1 in organ transplantation

Cyclosporin is a lipophilic cyclic polypeptide immunosuppressant that interferes with the activity of T cells chiefly via calcineurin inhibition. The original oil-based oral formulation of this drug (Sandimmun)l was characterised by high intra- and interpatient pharmacokinetic variability, with poor bioavailability in many patients; a novel microemulsion formulation (Neoral)1 was therefore developed to circumvent these problems. Studies show increases, attributable chiefly to improved absorption in patients who absorb the drug only poorly from the original formulation, in mean systemic exposure to cyclosporin with the microemulsion, with no clinically significant differences in tolerability or drug interaction profiles. Cyclosporin microemulsion is at least as effective as the oil-based formulation in renal, liver and heart transplant recipients, with trends towards decreased incidence of acute rejection with the microemulsion formulation in some (statistically significant in a few) trials. Cyclosporin microemulsion and tacrolimus appear to have similar efficacy in preventing acute rejection episodes in most renal, pancreas-kidney, liver and heart transplant recipients. However, there are indications of superior efficacy for tacrolimus in some trials, particularly in the prevention of severe acute rejection and in Black transplant recipients. Current 12-month data also indicate equivalent efficacy of sirolimus in renal transplantation. Conversion from the oil-based to microemulsion formulation in stable renal, liver and heart transplant recipients is achievable with no change in acute rejection rates. The addition of an anti-interleukin-2 receptor monoclonal antibody and/or mycophenolate mofetil to cyclosporin microemulsion plus corticosteroids decreases rates of acute rejection; corticosteroid withdrawal without increased acute rejection rates was also achieved on the addition of these agents in some trials. Pharmacoeconomic analyses have shown savings in direct healthcare costs in kidney or liver transplantation when cyclosporin microemulsion is used in preference to the oil-based formulation, although studies incorporating indirect costs or expressing costs in terms of therapeutic outcomes are currently unavailable.

CONCLUSIONS

The introduction of cyclosporin microemulsion has consolidated the place of the drug as a mainstay of therapy in all types of solid organ transplantation; research into optimisation of outcomes through more effective therapeutic monitoring in patients receiving this formulation is ongoing. Several novel immunosuppressants have been introduced in recent years: further clinical and pharmacoeconomic research will be needed to clarify the relative positioning of these agents, particularly with respect to specific patient groups. Other new drugs (basiliximab/daclizumab and mycophenolate mofetil) offer particular advantages when used in combination with cyclosporin.

Cardiovascular risk factors in renal transplant patients: cyclosporin A versus tacrolimus

The hypertensive and hyperlipidemic effects of cyclosporin A (CsA) may contribute to the high cardiovascular morbidity in renal transplant patients and to the development of chronic transplant nephropathy. Tacrolimus is reported to have less effect on BP and lipids, but steroids, other drugs, and renal function may confound this. This study assessed 24-h BP and lipid profile in stable renal transplant recipients (n = 17) while they were receiving CsA, after 4 wk of receiving tacrolimus, and again after 4 wk of receiving CsA. Antihypertensives were stopped at least 3 wk before. A few patients used low-dose steroids and lipid-lowering drugs, which were not changed during the study. Mean daytime BP decreased from 149 +/- 12 and 95 +/- 8 mmHg to 138 +/- 13 and 87 +/- 9 mmHg (P: < 0.001) after patients were switched to tacrolimus. Mean nighttime BP also decreased, from 140 +/- 12/86 +/- 7 mmHg to 132 +/- 17/79 +/- 10 mmHg (P: < 0.05). Total and low-density lipoprotein cholesterol decreased from 6.1 +/- 0.7 and 3.84 +/- 0.79 mmol/L to 5.1 +/- 0.8 and 2.98 +/- 0.75 mmol/L (P: < 0.001). Return to CsA caused an increase in BP and cholesterol to values similar as during the first CsA period. The conclusion is that tacrolimus has fewer unfavorable effects on BP and lipids than does CsA. Elective conversion from CsA to tacrolimus in stable renal transplant recipients may lead to attenuation of cardiovascular morbidity and chronic transplant nephropathy in the long term.

Dietary glycine and renal denervation prevents cyclosporin A-induced hydroxyl radical production in rat kidney

Cyclosporin A (CsA) nephrotoxicity is associated with renal hypoxia and increases in free radicals in the urine. This study was designed to elucidate the mechanism of radical production caused by CsA. Pretreatment of rats with CsA (25 mg/kg, i.g.) for 5 days decreased glomerular filtration rates by 65%, an effect largely prevented by both dietary glycine (5%) or renal denervation. CsA dissolved in olive oil produced a 6-line alpha-(4-pyridyl 1-oxide)-N-tert-butylnitrone (4-POBN)/free radical signal in the urine, which partitioned predominantly into the aqueous phase after chloroform extraction (i.e., it is water soluble). Dimethyl sulfoxide (DMSO) is attacked by the hydroxyl radical to produce a methyl radical; administration of CsA with [(12)C]DMSO produced two radical species in urine, one with hyperfine coupling constants similar to the 4-POBN/methyl radical adduct found in aqueous solution. CsA given with [(13)C]DMSO produced a 12-line spectrum, confirming the formation of hydroxyl radicals. The methyl radical produced by the hydroxyl radical represented 62% of radicals detected in urine but only 15% in bile. Therefore, hydroxyl radicals are produced largely in the kidney. Free radicals in urine were increased about 5-fold by CsA, an effect completely blocked by the inhibitory neurotransmitter, glycine, or by renal denervation. CsA infusion for 30 min increased efferent renal nerve activity 2-fold, and dietary glycine (5%) totally blocked this phenomenon. Taken together, these data are consistent with the hypothesis that CsA increases hydroxyl radical formation by increasing renal nerve activity resulting in vasoconstriction and hypoxia-reoxygenation. Glycine blunts the effect of CsA on the renal nerve, which explains, in part, prevention of nephrotoxicity.

Cyclosporine A modulates baroreceptor function in kidney transplant recipients

Cyclosporine has been described to increase the sympathetic tone. Alterations in sympathetic tone may contribute to baroreceptor dysfunction. Therefore, in this study baroreceptor function in 20 kidney transplant recipients was investigated under both low and high cyclosporine whole blood concentrations using the sequence analysis technique. The sympathetic nerve activity was estimated by calculating the low frequency oscillation of heart rate and blood pressure following Fast Fourier Transformation (FFT). Besides cyclosporine, azathioprine and prednisolone no other drugs were used. The increase in cyclosporine whole blood levels (from 101+/-13.4 ng/ml to 469+/-52 ng/ml) did not change mean arterial blood pressure significantly (83.7+/-2.5 vs. 82.2+/-2.0 mm Hg). Baroreflex sensitivity in +PI/+RR (+pulsinterval/+blood pressure) sequences, however, increased from 11.2+/-0.4 to 13.0+/-0.5 ms/mm Hg, whereas it was reduced in -PI/-RR (-pulsinterval/-blood pressure) sequences (14.4+/-0.3 to 12.5+/-1.1 ms/mm Hg). The increase in cyclosporine whole blood concentrations was associated with an increase in low frequency oscillation of heart rate (430+/-12 to 461+/-13) and blood pressure (452+/-9 to 469+/-12), indicating an enhanced sympathetic tone. Our results provide evidence that cyclosporine A by itself alters baroreceptor function. An imbalance between the sympathetic and parasympathetic nervous system due to an enhanced sympathetic tone may explain the reduction in -PI/-RR and the increase in +PI/+RR sequence baroreflex sensitivity.

Cyclosporin nephrotoxicity: pathophysiology and comparison with FK-506

At the end of an era of almost exclusive use of cyclosporin A, there have been significant advances in the understanding of its immunosuppressive effects, whereas there is still uncertainty about the mechanisms underlying its nephrotoxicity. The recently introduced FK-506, in spite of its undeniable clinical advantages, has subsequently been proved to have rather similar nephrotoxicity. This paper reviews recent data on cyclosporin A and FK-506 nephrotoxicity, with emphasis on: first, the haemodynamic, functional and structural features; second, the potential mediators; and third, the relationship with some immunosuppressive mechanisms involved to give insights into the pathophysiology.