Cyclosporin A inhibits endothelium-dependent, prostanoid-induced relaxation in human subcutaneous resistance vessels

NaHS or Lovastatin Attenuates Cyclosporine A-Induced Hypertension in Rats by Inhibiting Epithelial Sodium Channels

The use of cyclosporine A (CsA) in transplant recipients is limited due to its side effects of causing severe hypertension. We have previously shown that CsA increases the activity of the epithelial sodium channel (ENaC) in cultured distal nephron cells. However, it remains unknown whether ENaC mediates CsA-induced hypertension and how we could prevent hypertension. Our data show that the open probability of ENaC in principal cells of split-open cortical collecting ducts was significantly increased after treatment of rats with CsA; the increase was attenuated by lovastatin. Moreover, CsA also elevated the levels of intracellular cholesterol (Cho), intracellular reactive oxygen species (ROS) via activation of NADPH oxidase p47phox, serum- and glucocorticoid-induced kinase isoform 1 (Sgk1), and phosphorylated neural precursor cell-expressed developmentally downregulated protein 4-2 (p-Nedd4-2) in the kidney cortex. Lovastatin also abolished CsA-induced elevation of α-, ß-, and γ-ENaC expressions. CsA elevated systolic blood pressure in rats; the elevation was completely reversed by lovastatin (an inhibitor of cholesterol synthesis), NaHS (a donor of H2S which ameliorated CsA-induced elevation of reactive oxygen species), or amiloride (a potent ENaC blocker). These results suggest that CsA elevates blood pressure by increasing ENaC activity via a signaling cascade associated with elevation of intracellular ROS, activation of Sgk1, and inactivation of Nedd4-2 in an intracellular cholesterol-dependent manner. Our data also show that NaHS ameliorates CsA-induced hypertension by inhibition of oxidative stress.

Renal function and cardiovascular risk profile after conversion from ciclosporin to tacrolimus: prospective study in 80 liver transplant recipients

BACKGROUND

Increased risk of cardiovascular and cerebrovascular disease in liver transplant recipients results in particular from the side effects of calcineurin inhibitor-based immunosuppressive therapy. Several studies have demonstrated a more favourable outcome for patients receiving tacrolimus (TAC) as compared with ciclosporin (CS).

AIM

To investigate the effects of conversion from CS to TAC on cardiovascular risk factors and renal function in liver transplant recipients.

METHODS

In a prospective study, all except two patients had chronic kidney disease stages 2-4 (n = 80), according to estimated glomerular filtration rate using the abbreviated Modification of Diet in Renal Disease equation.

RESULTS

Conversion was accompanied with a mean decrease of total cholesterol from 194.6 +/- 54.0 mg/dL to 175.8 +/- 44.2 mg/dL (P < 0.001), low density lipoprotein cholesterol from 106.7 +/- 39.2 mg/dL to 90.9 +/- 28.6 mg/dL (P < 0.001) and mean arterial blood pressure values from 102.2 +/- 13.2 mm Hg to 95.9 +/- 11.7 mm Hg (P < 0.001). Renal function remained stable. No cases of de novo diabetes mellitus were identified. The Framingham risk score was significantly reduced from 5.2 +/- 4.4 at baseline to 4.4 +/- 5.3 after 12 months (P = 0.006).

CONCLUSIONS

Conversion from CS to TAC has been shown to improve the cardiovascular risk profile and may retard further decline of renal function after liver transplantation.

Increased vascular resistance and not salt retention characterizes cyclosporine A-induced hypertension: report in an anuric patient

Cyclosporine A (CsA) use is associated with hypertension in most solid-organ transplant recipients. The mechanisms of CsA-induced hypertension have not been fully elucidated and are still controversial. We present a case of CsA-induced hypertension who was anuric and receiving hemodialysis, and in whom noninvasive cardiothoracic bioimpedence revealed elevated systemic vascular resistance without evidence of fluid-volume overload. We briefly discuss the possible mechanisms of CsA-induced hypertension in light of this information.

Cyclosporine enhances vasorelaxation in coronary but not pulmonary artery after 16-hour preservation with UW solution

Cyclosporine (CsA), a calcineurin inhibitor, has been associated with endothelial dysfunction in transplant patients. Human and in vitro studies suggest that CsA produces endothelial dysfunction by impairing vascular endothelium-dependent relaxation. However, little is know about the CsA effects to modulate the vasorelaxation after prolonged graft preservation. In this study using a protocol designed to eliminate the influences of infusion pressure and shear stress, we evaluated the effect of CsA on vasorelaxation of coronary and pulmonary arteries after 16-hour University of Wisconsin (UW) solution preservation.

Variations in endothelial function and arterial compliance during the menstrual cycle

Female sex hormones have been implicated in the cardioprotection of premenopausal women. However, the cardiovascular actions of these hormones and the effects of their natural fluctuations during the menstrual cycle are not fully understood. We studied changes in vascular function during the menstrual cycle in 15 healthy premenopausal women. Four noninvasive procedures were performed during the early follicular (EF), late follicular (LF), early luteal (EL), and late luteal (LL) phases: flow-mediated dilatation (FMD) of the brachial artery during reactive hyperemia, laser Doppler velocimetry (LDV) with direct current iontophoresis of acetylcholine (ACh) and nitroprusside, whole body arterial compliance (WBAC), and pulse wave velocity. Hormone levels were consistent with predicted cycle phase and showed that all subjects ovulated during the cycle studied. FMD, LDV with ACh, and WBAC varied cyclically, with significant increases from the F to LF phase, sharp falls in the EL phase, and significant recoveries in the LL phase. These changes were most marked for FMD [EF, 8.8 +/- 0.6% (mean +/- SEM); LF, 10.0 +/- 0.7; EL, 4.2 +/- 0.6; LL, 8.6 +/- 0.9] and the LDV response to ACh (EF, 2.7 +/- 0.2 V/min; LF, 3.3 +/- 0.4; EL, 1.8 +/- 0.3; LL, 2.7 +/- 0.4). WBAC changed similarly (EF, 0.58 +/- 0.08 arbitrary units; LF, 0.84 +/- 0.06; EL, 0.65 +/- 0.05; LL, 0.68 +/- 0.06). Sodium nitroprusside-induced vasodilatation decreased significantly from EF to EL, with no other significant difference, and pulse wave velocity did not vary significantly over the four time points. Conductance and resistance artery endothelial reactivity and smooth muscle sensitivity to nitric oxide and arterial compliance are modulated significantly in response to the changing hormonal patterns of the menstrual cycle. These findings emphasize the importance of menstrual phase in the interpretation of data on endothelial function and may provide insights into the mechanisms underlying sex differences in cardiovascular risk and other disease processes in premenopausal women.

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.

Wavelet analysis of oscillations in the peripheral blood circulation measured by laser Doppler technique

The wavelet transform technique, a time-frequency method with logarithmic frequency resolution, was used to analyze oscillations in human peripheral blood flow measured by laser Doppler flowmetry. The oscillations extended over a wide frequency scale and their periods varied in time. Within the frequency range studied, 0.0095-1.6 Hz, five characteristic oscillations were revealed, arising from both local and central regulatory mechanisms. After the insertion of endothelium-dependent and endothelium-independent vasodilators the spectra of blood flow markedly differed in the frequency interval 0.0095-0.02 Hz. In this way it was demonstrated that endothelial activity is a rhythmic process that contributes to oscillations in blood flow with a characteristic frequency of around 0.01 Hz. The study illustrates the potential of laser Doppler flowmetry combined with dynamical systems analysis for studies of both the micro- and macroscopic mechanisms of blood flow regulation in vivo.

Role of sympathetic nervous system in cyclosporine-induced rise in blood pressure

To clarify the role of the sympathetic nervous system in the development of cyclosporine A (CsA)-induced rise in blood pressure (BP), the effects of CsA on 24-hour ambulatory BP (ABP) were studied in patients with familial amyloid polyneuropathy (FAP) who underwent a liver transplantation. On the basis of autonomic function tests, patients with absent or mild-to-moderate sympathetic damage (Group A, n=11, age 29 to 43 years, disease duration 2 to 6 years) and patients with severe sympathetic damage (Group B, n=9, age 27 to 38 years, disease duration 3 to 9 years) were identified. Both groups were followed for 1 year. The daily doses of CsA and the CsA whole blood trough levels between the groups did not differ. Pretransplantation values of daytime and nighttime ABP were, respectively, 117+/-8/76+/-7 mm Hg and 108+/-12/68+/-9 mm Hg in group A and 107+/-6/66+/-4 mm Hg (P<0.05 group A versus group B) and 102+/-6/62+/-4 mm Hg in group B. In response to CsA, BP increased in all patients, but more so in patients of group B than in patients of group A. One year after transplantation, daytime and nighttime ABP had increased by 6+/-9/3+/-11% and 12+/-10/14+/-14% in group A and by 12+/-6/13+/-10% (P<0.05) and 21+/-11/27+/-21% (P<0.01) in group B. In both groups, the increase in nighttime ABP was greater than the increase in daytime ABP, which resulted in an attenuation or, even, a reversal of the diurnal BP rhythm. Because the rise in BP was greater in patients with more advanced sympathetic dysfunction, the sympathetic nervous system appears to counteract the CsA-induced rise in BP rather than causing it. This implies involvement of factors other than sympathetic activation in the pathogenesis of CsA-induced rise in BP in patients with familial amyloid polyneuropathy.

Oscillations in the human cutaneous blood perfusion signal modified by endothelium-dependent and endothelium-independent vasodilators

The purpose of the present study was to compare the effects of endothelium-dependent [acetylcholine (ACh)] and endothelium-independent [sodium nitroprusside (SNP)] vasodilators on the oscillatory components of the cutaneous blood perfusion signals in humans. The unstimulated basal blood perfusion and the blood perfusion during iontophoretically delivered ACh and SNP were measured using laser Doppler flowmetry (LDF). The wavelet transform was calculated before spectral analysis of the measured signals. In the frequency interval from 0.0095 to 1.6 Hz the LDF signal consists of oscillations with five different characteristic frequencies. In addition to the cardiac (1 Hz) and respiratory (0.3 Hz) rhythms, three other oscillations in the regions around 0.1, 0.04, and 0.01 Hz were detected. The oscillations with the different frequencies were observed in unstimulated blood flow and also during stimulation with ACh and SNP. Compared to the unstimulated blood flow, both ACh and SNP increased the mean amplitude of the total spectrum (P < 0. 005 for both substances). The only significant difference between the effects of ACh and SNP was observed in the amplitude of oscillations with the frequency of around 0.01 Hz. ACh increased the absolute amplitude of this frequency to a greater extent than SNP in athletes (P = 0.03), whereas only a trend was observed in controls (P = 0.2). The relative amplitude, defined as the ratio between the absolute amplitude of a particular frequency interval and the mean amplitude of the total spectrum, was also higher for ACh compared to SNP both in controls (P = 0.008) and in athletes (P = 0.004), only for oscillations with the frequency of around 0.01 Hz. We conclude that ACh selectively influences the oscillatory component of around 0.01 Hz in the cutaneous blood perfusion signal to a greater extent than SNP. This finding indicates that endothelium-mediated vasodilatation is manifested as oscillations with a repetition time of approximately 1 min. The mechanisms for the endothelial dependency of this frequency remain to be elucidated. Our data indicate that spectral analysis based on wavelet transform of the cutaneous perfusion signal can be used clinically to investigate endothelial function. The described noninvasive method might be used to evaluate endothelial function for research, for diagnostic purposes, and maybe also to assess effects of therapy in cardiovascular diseases.

Role of nitric oxide in cyclosporine A-induced hypertension

Cyclosporine A (CsA) is an immunosuppressive agent that also causes hypertension. The effect of CsA on vascular responses was determined in Sprague-Dawley rats and isolated rat aortic rings. Male rats weighing 250 to 300 g were given either CsA (25 mg. kg-1. d-1) in olive oil or vehicle by intraperitoneal injection for 7 days. CsA administration produced a 42% increase (P<0.001) in mean arterial pressure (MAP) that reached a plateau after 3 days. Conversely, the levels of both nitrate/nitrite, metabolites of nitric oxide (NO), and cGMP, which mediates NO action, decreased by 50% (P<0.001) and 35% (P<0.001), respectively, in the urine. Thoracic aortic rings from rats treated with CsA and precontracted with endothelin (10(-9) mol/L) showed a 35% increase (P<0.001) in tension, whereas endothelium-dependent relaxation induced by acetylcholine (ACh, 10(-9) mol/L) was inhibited 65% (P<0.001) compared with that in untreated rats. This response was similar to that of endothelium-denuded aortic rings from untreated rats in which ACh-induced relaxation was completely abolished (P<0.001), but relaxation induced by S-nitroso-N-acetylpenicillamine (SNAP, 10(-8) mol/L) was unaffected (P<0.001). ACh-induced formation of both nitrate/nitrite and cGMP by both denuded and CsA-treated aortic rings was inhibited 95% (P<0.001) and 65% (P<0.001), respectively, compared with intact aortic rings. The effects of CsA were reversed both in vivo and in vitro by pretreatment with L-arginine (10 mg. kg-1. d-1 IP), the precursor of NO. There were no changes in MAP and tension in rats treated with L-arginine alone. In summary, CsA inhibits endothelial NO activity, with resulting increases in MAP and tension, and this inhibition can be overcome by parenteral administration of L-arginine.

Exercise capacity in heart transplant recipients: relation to impaired endothelium-dependent vasodilation of the peripheral microcirculation

OBJECTIVES

The aim of this study was to examine the responses to endothelium-dependent and -independent vasodilators on the peripheral microcirculation in heart transplant recipients in relation to exercise capacity compared with that in healthy controls.

BACKGROUND

Impaired endothelium-dependent vasodilation of the microcirculation may play an important role in the limitation of exercise capacity after heart transplantation.

METHODS

Microvascular perfusion responses to four graded levels of iontophoretically applied 1% acetylcholine (endothelium-dependent vasodilator) and 1% sodium nitroprusside (SNP) (endothelium-independent) in the forearm skin of 42 transplant recipients and 16 age-matched controls were determined by laser Doppler perfusion measurements. Maximal exercise capacity was assessed by peak oxygen uptake (peak VO2) during progressive, symptom-limited, upright bicycle exercise.

RESULTS

With similar baseline perfusion levels in transplant recipients and controls (4.2 +/- 0.4 vs 4.6 +/- 0.6 arbitrary units [AU]), the increases in perfusion to acetylcholine, but not to SNP, were significantly attenuated in the transplant recipients: 7.0 +/- 1.0 vs 11.0 +/- 2.0, 12.7 +/- 1.5 vs 21.0 +/- 2.8, 21.0 +/- 1.9 vs 32.7 +/- 2.4, and 28.0 +/- 1.6 vs 39.2 +/- 2.4 AU, respectively (all p < 0.01). Peak VO2 was significantly lower in the transplant recipients (22.4 +/- 1.0 vs 38.0 +/- 2.9 ml/kg/min; p < 0.01). Furthermore, acetylcholine responses of the transplant recipients correlated closely to their peak VO2, irrespective of level of application (r = 0.63; p < 0.001, all four acetylcholine responses taken together), whereas no such correlation was found for SNP responses. In the control group, no relation was observed in acetylcholine/SNP responses to peak VO2.

CONCLUSIONS

Exercise limitation in transplant recipients appears strongly associated with attenuated endothelium-dependent vasodilation of the peripheral microcirculation.

Effect of heart transplantation on impaired peripheral microvascular perfusion and reactivity in congestive heart failure

Whether reduced peripheral blood flow in congestive heart failure is reversed after heart transplantation, has not been closely examined. We therefore studied skin microvascular resting perfusion and reactivity in patients pre- and postoperatively. Resting digital skin perfusion, together with the responses to cold pressor test, postocclusive reactive hyperemia and direct skin heating were examined with laser Doppler perfusion measurements. We examined 28 patients with congestive heart failure and 14 of these patients after heart transplantation and compared them to 13 healthy controls. Measurements were performed within 3 months preoperatively and 12 days, 1, 2, 3 and 6 months postoperatively. Patients with congestive heart failure had significantly lower resting perfusion levels than controls and demonstrated attenuated responses to both stimuli of vasodilation (all P<0.01). While peak hyperemic responses improved significantly after transplantation, postocclusive area under the hyperemic curve decreased further, and none of these variables were normalized after 6 months. In contrast, minimal perfusion during cold pressor test increased from a significantly lower level in the patients with congestive heart failure (P<0.05), to a level similar to that of the controls within 12 days postoperatively. Thus, skin microvascular perfusion and reactivity improve, but are not normalized within 6 months of transplantation. Both pre- and postoperative factors may be involved in maintaining a dysfunction of the peripheral microcirculation, which may contribute to exercise intolerance and hypertension in heart transplant recipients.

Forearm vasorelaxation in hypertensive renal transplant patients: the impact of withdrawal of cyclosporine

OBJECTIVE

To determine whether cyclosporine A-induced hypertension in renal transplant recipients is accompanied by impairment of endothelium-dependent vasodilatation, which has been suggested by in-vitro and in-vivo animal experiments.

DESIGN AND METHODS

In-vivo endothelium-dependent and endothelium-independent vasodilatation, and plasma concentrations of vasoactive hormones in 16 renal transplant patients were determined while they were being treated with cyclosporine A, and 16 weeks later, after their treatment had been changed to azathioprine therapy. The vasodilator response of the forearm vascular bed was measured by strain gauge venous occlusion plethysmography during intra-arterial infusion of acetylcholine (endothelium-dependent vasodilatation) and nitroprusside (endothelium-independent vasodilatation). Postischemic reactive flow was measured after 10 min of arterial occlusion. In addition, plasma concentrations of norepinephrine, and the prostanoids prostaglandin E2 and thromboxane B2, and also concentration of cyclosporine A in blood, were measured. Glomerular filtration rate and renal blood flow were estimated 1 day before the plethysmography study during each treatment period.

RESULTS

Upon changing from cyclosporine A to azathioprine treatment, mean arterial pressure fell significantly by 12+/-3% (P< 0.05). Glomerular filtration rate and renal blood flow increased by 13+/-5 and 19+/-8%, respectively (both P< 0.05), while renal vascular resistance fell by 48+/-11% (P< 0.01). Both baseline forearm blood flow and baseline forearm resistance did not change after conversion (5.7+/-0.7 versus 4.9+/-0.6 ml/100 ml/min, and 27.3+/-4.2 versus 26.2+/-3.2 arbitrary units). The absolute and relative forearm blood flow responses, and forearm vascular resistance responses to infusions of acetylcholine and nitroprusside were similar during treatments with cyclosporine A and azathioprine. Peak postischaemic forearm blood flow was 42+/-12% higher during cyclosporine A treatment than it was during azathioprine treatment (P< 0.05), but the minimal postischaemic forearm vascular resistance did not differ for these treatments. Plasma prostaglandin E2 and thromboxane B2 levels decreased by 34+/-7 and 45+/-8%, respectively, after changing treatment, but norepinephrine levels did not change.

CONCLUSIONS

Our data indicate that cyclosporine A-induced hypertension in renal transplant recipients is not accompanied by an increase in forearm vascular resistance. In addition, changing from cyclosporine A to azathioprine treatment did not cause changes in endothelial vasodilator functioning, although mean arterial pressure decreased significantly. Our results do not support the hypothesis that attenuation of endothelial vasodilator functioning contributes to the development of cyclosporine A-induced hypertension.

Selective impairment of endothelium-mediated vasodilation in liver transplant recipients with cyclosporin A-induced hypertension

Arterial hypertension is commonly observed in orthotopic liver transplantation (OLT) recipients receiving cyclosporin A (CsA), but the precise pathogenetic mechanisms remain partially unknown. The aim of this study was to investigate endothelium-dependent and -independent dilation and adrenergic constriction of resistance vessels of OLT recipients treated with CsA. Vascular reactivity was examined in 22 OLT patients, 10 with and 12 without arterial hypertension, and in 10 control subjects by assessing the forearm blood flow response to the brachial artery infusion of increasing concentrations of methacholine chloride, sodium nitroprusside, and phenylephrine. In 10 OLT patients, the response to methacholine was also examined after acetylsalicylate. The ratio of serum nitrite and nitrate to serum creatinine was lower (P < .05) in OLT patients with hypertension than in nonhypertensive patients and controls. Basal forearm flow was similar in the three groups. Methacholine vasodilation was impaired in the hypertensive patients as shown by a lower maximum forearm vasodilator response and a shift in the dose response curve to methacholine to the right compared with the nonhypertensive OLT patients and the controls. The response to methacholine was not modified after salicylate. Forearm flow response to nitroprusside was similar in the three groups. No differences between the patients and the controls were found in the maximum forearm flow contraction in response to phenylephrine. An impairment in endothelium-dependent vasodilation could mediate arterial hypertension in OLT patients immunosuppressed with CsA.

Cyclosporin A increases nitric oxide activity in vivo

The use of cyclosporine is complicated by its vaso-constrictive actions. In vitro cyclosporine has been associated with both decreased endothelium-dependent vasodilatation and increased nitric oxide activity. We studied the interaction between cyclosporine and endothelium-derived nitric oxide in seven healthy volunteers. Using venous-occlusion plethysmography, we measured forearm blood flow during intra-arterial infusion of serotonin, which in the concentrations used is a selective agonist of endothelial nitric oxide release, or NG-monomethyl-L-arginine, a specific inhibitor of nitric oxide synthase, during coinfusion of saline or cyclosporine (75 micrograms/min), respectively. During coinfusion of cyclosporine, forearm blood flow increased on maximal serotonin infusion from 2.9 (SE, 0.2) to 8.1 (0.9) mL/100 mL per minute in forearm tissue, which was significantly higher than the increase during saline coinfusion (3.0[0.3] to 6.0 [0.5]; P < .05). Cyclosporine infusion during a "free" nitric oxide system had no effect on basal forearm blood flow, but in significantly decreased forearm blood flow (21.7[2.8]%; P < .05) during fixed nitric oxide activity. These data suggest that acute administration of cyclosporine enhances both basal and receptor-stimulated nitric oxide activity. The mechanism is not clear but may include cyclosporine-induced shear stress as well as direct effects of cyclosporine. The latter was supported by our observation that gene expression of the enzyme nitric oxide synthase III was enhanced by approximately 50% after coincubation with cyclosporine. In conclusion, the present observation demonstrates that nitric oxide constitutes an important regulating mechanism that protects against cyclosporine-associated vasoconstriction in vivo.

Pharmacology of immunosuppressive medications used in renal diseases and transplantation

As understanding of the molecular basis for the immune response has expanded rapidly, so have the possibilities for designing therapeutic interventions that are more effective, more specific, and safer than current treatment options. The promise of therapeutic advances in the future is based on the rapidly expanding insights into the pathogenesis of abnormal immunologic reactions. Nowhere is the understanding of molecular mechanisms, pathophysiology, and targeted therapy more relevant than in the field of renal transplantation, which makes up much of the clinical database for the use of immunosuppressive therapy for renal disease. Despite the recent advances in basic immunology, clinical validation of new agents and approaches is lacking for most drugs at present. This review will focus in the pharmacology of agents used in the therapy of immunologic renal disease and in renal transplantation. It should be recognized that clinical pharmacology and experience with newer agents is limited, and potential utility is based largely on experimental data.

Skin blood flow responses to the iontophoresis of acetylcholine and sodium nitroprusside in man: possible mechanisms

1. The mechanisms involved in the human skin blood flow responses to iontophoretic application of acetylcholine (ACH; delivered using an anodal charge) or sodium nitroprusside (SNP; administered with a cathodal charge) are unclear. The aims of this study were to investigate possible contributions of prostaglandin production to the increase in skin blood flow induced following the iontophoresis of ACh and to investigate possible contributions from local sensory nerves to the perfusion responses induced by ACh, SNP and their vehicles. 2. The contribution of prostaglandins to the ACh response was determined in a randomized double-blind study of eight healthy subjects, who were studied on two occasions. Basal responses to ACh were measured before the oral administration of 600 mg soluble aspirin in diluted orange juice (1 occasion or orange juice (1 occasion) and again 30 min after the drink. The contribution of local sensory nerve activation to the responses to ACh and ACh vehicle (8 subjects) and to SNP and SNP vehicle (7 subjects) was assessed. EMLA (5%) (a eutectic mixture of lignocaine and prilocaine) and placebo cream were applied to two separate areas on the forearm in a double-blind randomized manner 2 h before drug responses were measured. In all studies the skin microcirculation responses to iontophoretically applied drug vehicle (1 site) and drug (2 sites) were recorded by laser Doppler perfusion imaging. 3. The increase in forearm skin perfusion (P < 0.001) in response to the iontophoresis of ACh minus the response to ACh vehicle was not significantly different following placebo or aspirin administration. The increase in forearm skin red blood cell flux (P < 0.001) in response to the iontophoresis of ACh minus the response to ACh vehicle was not significantly different at the placebo-compared with the EMLA-treated site. THe small increase in perfusion (P < 0.001) in response to the iontophoresis of ACh vehicle was significantly inhibited at the EMLA-compared with the placebo-treated site (P < 0.05). The marked increase in perfusion (P < 0.001) in response to the iontophoresis of SNP vehicle was significantly inhibited at the EMLA-compared with the placebo-treated site (P < 0.01). 4. These data suggest that in healthy volunteers: (1) mechanisms other than prostaglandin production and local sensory nerve activation may be involved in the increase in skin perfusion observed following the iontophoretic application of ACh; and (2) stimulation of local sensory nerves may be responsible for the increase in tissue perfusion observed following the iontophoretic application of either ACh vehicle or SNP vehicle.

Cyclosporine impairs vasodilation without increased sympathetic activity in humans

Hypertension and nephrotoxicity frequently complicate treatment with cyclosporine; two suggested mechanisms are increased sympathetic activity and altered vascular reactivity. It is difficult to assess these mechanisms in patients receiving cyclosporine after transplantation because of the accompanying major physiological alterations. Therefore, we studied 12 patients with rheumatoid arthritis twice--while they were taking and not taking cyclosporine. We measured vascular response in the dorsal hand vein using the linear variable differential transformer technique. Cyclosporine treatment significantly attenuated vasodilation induced by 60 ng/min isoproterenol (no cyclosporine, 19.8 +/- 3.5% versus cyclosporine, 7.9 +/- 2.2%; P = .02) and prostaglandin E1 at 1000 pg/min (no cyclosporine, 72.6 +/- 10.2% versus cyclosporine 45.6 +/- 9.0%) and 2000 pg/min (no cyclosporine, 100.8 +/- 14.7% versus cyclosporine, 68.6 +/- 8.0%; F = 5.47, P = .047). However, neither vascular response to phenylephrine or nitroglycerin nor sympathetic activity assessed by measurement of norepinephrine spillover with a radioisotope dilution technique was affected by cyclosporine (no cyclosporine, 516.1 +/- 47.9 ng/min versus cyclosporine, 476.6 +/- 51.8 ng/min; P = .42). Cyclosporine impaired venodilation in response to two agonists that act through adenylate cyclase without altering alpha-agonist-induced venoconstriction or sympathetic activity. Therefore, in humans impaired vasodilation rather than sympathetic activation or enhanced vasoconstriction may be an important mechanism for the alterations of vascular tone that occur after long-term cyclosporine administration.

Cyclosporine-induced hypertension after transplantation

OBJECTIVE

To describe the features and mechanisms of posttransplantation hypertension and suggest appropriate management of the disorder.

DESIGN

We review our own experience and reports from the literature on hypertension in cyclosporine A (CSA)-treated transplant recipients.

RESULTS

Soon after immunosuppression with CSA and corticosteroids, hypertension develops in most patients who undergo transplantation. The blood pressure increases, which are usually moderate, occur universally because of increased peripheral vascular resistance. Disturbances in circadian patterns of blood pressure lead to loss of the normal nocturnal decline, a feature that magnifies hypertensive target effects. Changes in blood pressure sometimes are severe and associated with rapidly developing target injury, including intracranial hemorrhage, left ventricular hypertrophy, and microangiopathic hemolysis. The complex mechanisms that underlie this disorder include alterations in vascular reactivity that cause widespread vasoconstriction. Vascular effects in the kidney lead to reduced glomerular filtration and impaired sodium excretion. Many of these changes affect local regulation of vascular tone, including stimulation of endothelin and suppression of vasodilating prostaglandins. Effective therapy includes use of vasodilating agents, often calcium channel blocking drugs. Caution must be exercised to avoid interfering with the disposition of CSA or aggravating adverse effects relative to kidney and electrolyte homeostasis.

CONCLUSION

Recognition and treatment of CSA-induced hypertension and vascular injury are important elements in managing the transplant recipient.

Vasomotor responses in cyclosporin A-treated rats after chronic angiotensin blockade

Chronic angiotensin-converting enzyme (ACE) inhibition prevents endothelial dysfunction in hypertension and hypercholesterolemia. Long-term treatment with cyclosporin A impairs endothelium-dependent relaxations and augments contractions to angiotensin II in the rat aorta. The present study compares vasomotor responses to several vasoconstrictor and dilator stimuli after 6 weeks of oral treatment with either the angiotensin-converting enzyme inhibitor lisinopril (10 mg/kg per day), the angiotensin subtype 1 receptor antagonist D 8731 (10 mg/kg per day), cyclosporin A (15 mg/kg per day), or a combination of cyclosporin A with lisinopril or D 8731 (n = 15 rats per group). Twenty-four hours after the last treatment, aortic rings were mounted in organ chambers for measurement of isometric force. Endothelium-dependent relaxations to acetylcholine and calcium ionophore were impaired by cyclosporin A but not affected by the vasodilators. Cyclosporin A-induced endothelial dysfunction was prevented by cotreatment with lisinopril or D 8731. Relaxations to nitroglycerin, SIN-1, and forskolin were not affected by any treatment. Contractions to phenylephrine and serotonin were reduced by lisinopril but not by D 8731. In contrast, contractions to angiotensin II were augmented by cyclosporin A, lisinopril, and the combination of both but not by D 8731 or D 8731 plus cyclosporin A. The data suggest a role for angiotensin II in cyclosporin A-induced endothelial dysfunction. Chronic ACE inhibition reduces overall smooth muscle contractility. The selective augmentation of angiotensin II effects by ACE inhibition and cyclosporin A suggests upregulation of angiotensin receptors in the aortic smooth muscle by these treatments. Chronic angiotensin subtype 1 receptor blockade does not appear to affect angiotensin receptor function.

Vascular mechanisms of cyclosporin-induced hypertension in the rat

Numerous studies have explored the pathogenesis of cyclosporin A (CysA)-induced hypertension; however, none has assessed the impact of CysA treatment on resistance arteries in the setting of elevated blood pressure. Therefore, we studied the chronic effect of CysA on rat mesenteric artery resistance vessels (ex vivo). CysA (25 mg/kg per d for 7 d), but not vehicle, significantly raised systolic blood pressure (13.4 +/- 2.2 mmHg, P < 0.003, n = 9 per group). The resistance vessels from CysA-treated rats showed a small but significant decrease in norepinephrine sensitivity (P < 0.03) and a pronounced decrease in endothelium-dependent and -independent relaxation (P < 0.001) compared to controls. Endothelin-1 sensitivity tended to be diminished (P = 0.07). The direct (in vitro) effect of CysA was subsequently evaluated in resistance vessels from nontreated animals (n = 8) and exposed to CysA (2 micrograms/ml) for 24 h. As observed in vivo, CysA significantly decreased endothelium-dependent and -independent relaxations (P < 0.05) and attenuated norepinephrine sensitivity (P = 0.06). Methylene blue, a nitric oxide quencher, significantly inhibited the acetylcholine-induced relaxation in control, but not in CysA vessels, suggesting a selective action of CysA on the nitric oxide pathway. We conclude that CysA-induced hypertension is the consequence of a primary effect on resistance vessel relaxation, not increased vasoconstriction, as previously suggested.

Cyclosporine therapy after cardiac transplantation causes hypertension and renal vasoconstriction without sympathetic activation

BACKGROUND

Hypertension frequently complicates the use of cyclosporine A (CyA) therapy, and it has been suggested that sympathoexcitation may be the underlying mechanism in this form of hypertension.

METHODS AND RESULTS

To further investigate the possibility of a neurogenic mechanism for this hypertensive effect, we studied the effects of CyA on renal blood flow (n = 11), forearm blood flow (n = 8), and sympathetic nervous system activity, assessed by renal and whole-body radiolabeled norepinephrine plasma kinetics and muscle sympathetic nerve firing (using microneurography) in cardiac transplant recipients receiving CyA and a reference group of healthy age-matched control subjects (n = 17). In 11 cardiac transplant patients (2 hours after cyclosporine dose), renal blood flow was significantly lower than that in 8 control subjects (680 +/- 88 vs 1285 +/- 58 mL/min, P < .001). In 5 of these transplant patients, renal blood flow was measured before and for 2 hours after oral cyclosporine and fell progressively over this period, by 37% (P < .01). Total body and renal norepinephrine spillover rates in transplant patients were similar to those in control subjects (3070 +/- 538 vs 2618 +/- 313 pmol/min and 579 +/- 124 vs 573 +/- 95 pmol/min, respectively), and there was no progressive effect in the 2 hours after cyclosporine dosing. Forearm blood flow was increased 2 hours after CyA administration (1.74 +/- 0.31 to 3.12 +/- 0.50 mL x 100 mL-1 x min-1, P < .001), whereas mean arterial blood pressure and noninvasively determined cardiac output (indirect Fick method) were unchanged. Muscle sympathetic nerve discharge rates recorded in 6 of these transplant patients were not different from those in 9 healthy control subjects (37.9 +/- 10.1 vs 41.3 +/- 2.3 bursts per 100 beats per minute). During 90 to 120 minutes of recording after cyclosporine dosing, nerve firing rates remained unchanged.

CONCLUSIONS

CyA therapy causes acute renal vasoconstriction without accompanying systemic hemodynamic effects. These renal effects are nonneural, not being attributable to sympathoexcitation.

De novo hypertension after liver transplantation

Hypertension develops in most patients after transplantation when immunosuppression is based on cyclosporine and prednisone. The pathogenesis appears to be multifactorial but involves rapidly rising vasoconstrictor tone in renal and systemic vascular beds. Much of this tone reflects abnormal vascular function, characterized by impaired prostacyclin and EDRF effects, in conjunction with increased vasoconstriction due to endothelin and possibly other factors. Effective management of the transplant recipient depends on preventing excessive vasoconstriction, usually with calcium channel blocking agents.

Endothelin-1 release from the mesenteric arteries of cyclosporine-treated rats

The release of endothelin-1 from mesenteric arteries from cyclosporine-treated rats was measured by a specific enzyme immunoassay after purification of the perfusate on an immunoaffinity column. Mesenteric arteries from cyclosporine-treated rats (25 mg/kg per day for 6 weeks) released a significantly larger amount of endothelin-1 than arteries from vehicle-treated control rats (P less than 0.05). Serum creatinine levels were not significantly different in the two groups. These findings indicate that cyclosporine is a potential inducer of endothelin release from the mesenteric artery.