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Influence of antihypertensive drugs on renal microcirculation and renal hemodynamics in cyclosporine a-treated rats
Influence of Antihypertensive Drugs on Renal Microcirculation and Renal Hemodynamics in Cyclosporine A-Treated Rats U. Hillebrand, V. Kobelt, M. vOphoven, B. Suwelack, F. Matzkies, U. Gerhardt, J. Sindermann, and H. Hohage
S
INCE its introduction approximately 20 years ago, cyclosporine (CsA) is one of the most important immunosuppressive agents used in renal transplantation. Although CsA therapy has significantly improved graft survival rates in organ transplantation,1–3 its use is limitated due to a wide variety of side effects. A dose-dependent, frequently reversible decrease in glomerular filtration rate (GFR) is an additional complicating factor. As both angiotensin- converting enzyme (ACE) inhibitors and angiotensin II (A-II) receptor antagonists are known to exert nephroprotective effects, we aimed to clarify possible influences of these antihypertensive drugs on renal microcirculation and renal hemodynamics (measurements were done by laser doppler flowmetry) in cyclosporine CsA-treated rats. MATERIAL AND METHODS The experiments to study the effects of CsA with and without a combination of an ACE inhibitor or an A-II receptor antagonist on renal cortical microcirculation were performed on 20 male Wistar Kyoto rats (Charles River, Sulzfeld, Germany), delivered at a body weight of 175 to 200 g. The following procedures were all in accordance with the guiding principles for the care and use of animals in the field of physiologic science recommended by the Physiological Society in Germany.
Blood Pressure Arterial blood pressure was recorded from the carotid artery by a polyethylene catheter (0.5-mm inner diameter), connected to a small volume displacement pressure transducer (TSE, Bad Homburg, Germany), while heart rate was monitored simultaneously by triggering the phasic signal from the transducer. The phasic arterial blood pressure signal was filtered at 0.08 Hz to obtain mean arterial blood pressure.
Fig 1. Effects of vehicle, CsA, and combinations of CsA with quinapril (Qui) or losartan (Los) on renal microcirculation. The experiments were performed on at least five animals per group. Data are given as mean ⫾ SEM. * ⫽ P ⬍ .05.
Measurement of Renal Microcirculation Renal microcirculation was measured by surface laser Doppler probes (SP300, Oxford Optronics, Oxford, UK) connected to a flowmeter (Oxford Array, Oxford Optronics).
RESULTS
The animals received an intravenous infusion of CyA in the dosage of 1 mg/kg body weight. Thirty minutes after infusion renal microcirculation was significantly diminished (110 vs 90 LDF units, P ⬍ .05) (Fig 1). Simultaneous application of quinapril (0.1 mg/kg body weight) or losartan (2 mg/kg body weight) increased renal cortical microcirculation above control values (quinapril from 100 to 140 LDF units, P ⬍ .05; losartan from 110 to 155 LDF units, P ⬍ .05). Renal blood flow in CsA-treated animals was 7 mL/min vs
Continuous Measurement of Renal Blood Flow A midline abdominal incision was made, and the left kidney and the renal artery were freed from the surrounding fat and connective tissue by blunt dissection. The kidney was placed in a semicircular support. Transit-time flow probes (model 1RB, Transsonic Systems) filled with ultrasound coupling gel (Sonogel, Transsonic Systems) were positioned around the renal artery and connected to a two-channel small animal digital transit-time blood flowmeter (model T206, Transsonic).
From the Medizinische Klinik and Poliklinik, Universita¨tklinikum Mu¨nster, Mu¨nster, Germany. Supported by a grant from the German Ministery of Science and Education 01EC9801. Address reprint requests to U. Hillebrand, Medizinische Klinik and Poliklinik D, Universita¨tsklinikum Mu¨nster, Albert Schweitzer Str. 33, D-48129 Mu¨nster, Germany. E-mail: hohage@uni-muen ster.de
© 2002 by Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010
0041-1345/02/$–see front matter PII S0041-1345(02)03068-3
Transplantation Proceedings, 34, 1383–1384 (2002)
1383
1384
Fig 2. Renal blood flow after administration of vehicle, CsA, and combinations of CsA with quinapril or losartan on renal microcirculation. The experiments were performed on at least five animals per group. Data are given as mean ⫾ SEM. * ⫽ P ⬍ .05.
14 mL/min in control animals (Fig 2). Quinapril and losartan had no effect on renal blood flow alone. Simultaneous infusion of CsA and quinapril or CsA and losartan abolished both the negative effects of CsA on renal blood flow and the renal vascular resistance.
HILLEBRAND, KOBELT VOPHOVEN ET AL
is not completely understood. The fact that this decrease in GFR is rapidly reversible with removal of the drug suggests that hemodynamic factors play a critical role. Decreases in renal blood flow, significant increases in renal vascular resistance, and decreases in GFR have been reported after both acute and chronic administration of CsA in rats.4 Increased renal sympathetic nervous system activity may play a role in the renal hemodynamic alterations produced by CsA. Indeed, a marked increase in renal nerve activity after intravenous CsA administration has been reported. Renal denervation prevented the CsA-induced decrease in GFR noted in the intact kidneys. A protective effect was observed when rats were subjected to renal denervation or after administration of alpha receptor blocking agents.5,6 Increased peripheral renin activity has been reported in rats treated acutely or chronically with CsA.4, 7 The role of the angiotensin system in CsA-induced alterations in renal hemodynamics, however, is not clear. The results of the present study show that ACE inhibitors and angiotensin II receptor antagonists may prevent CsA-induced alterations of microcirculation and renal blood flow. A blood flow shift from the medulla toward the renal cortex may contribute at least in part to the increase of cortical microcirculation observed in animals treated with a combination of CsA and antihypertensive drugs. REFERENCES
DISCUSSION
The nephrotoxicity of CsA has been well documented in both humans and experimental models.1,3 The adverse effects of CsA on renal function include an acute, reversible, dose-dependent decrease in GFR; alterations in renal potassium handling; and a chronic, progressive interstitial fibrosis with irreversible renal damage. The mechanism of the acute reversible deterioration in GFR produced by CsA
1. Bennett WM: Int J Clin Pharmacol Ther 34:515, 1986 2. Perico N, Remuzzi G: Drugs 54:533, 1997 3. Morales JM, Andres A, Rengel M, et al: Nephrol Dial Transplant 16:121, 2001(suppl 4. Ajikobi DO, Novak P, Salevsky FC, et al: Ca J Physiol Pharmacol 74:964, 1996 5. Hohage H, Schlatter E, Greven J: Clin Nephrol 47:316, 1997 6. Hohage H, Hess K, Jahl C, et al: Clin Nephrol 48:346, 1997 7. Arendshorst WJ, Brannstrom K, Ruan X: J Am Soc Nephrol 10:149, 1999(suppl
S
INCE its introduction approximately 20 years ago, cyclosporine (CsA) is one of the most important immunosuppressive agents used in renal transplantation. Although CsA therapy has significantly improved graft survival rates in organ transplantation,1–3 its use is limitated due to a wide variety of side effects. A dose-dependent, frequently reversible decrease in glomerular filtration rate (GFR) is an additional complicating factor. As both angiotensin- converting enzyme (ACE) inhibitors and angiotensin II (A-II) receptor antagonists are known to exert nephroprotective effects, we aimed to clarify possible influences of these antihypertensive drugs on renal microcirculation and renal hemodynamics (measurements were done by laser doppler flowmetry) in cyclosporine CsA-treated rats. MATERIAL AND METHODS The experiments to study the effects of CsA with and without a combination of an ACE inhibitor or an A-II receptor antagonist on renal cortical microcirculation were performed on 20 male Wistar Kyoto rats (Charles River, Sulzfeld, Germany), delivered at a body weight of 175 to 200 g. The following procedures were all in accordance with the guiding principles for the care and use of animals in the field of physiologic science recommended by the Physiological Society in Germany.
Blood Pressure Arterial blood pressure was recorded from the carotid artery by a polyethylene catheter (0.5-mm inner diameter), connected to a small volume displacement pressure transducer (TSE, Bad Homburg, Germany), while heart rate was monitored simultaneously by triggering the phasic signal from the transducer. The phasic arterial blood pressure signal was filtered at 0.08 Hz to obtain mean arterial blood pressure.
Fig 1. Effects of vehicle, CsA, and combinations of CsA with quinapril (Qui) or losartan (Los) on renal microcirculation. The experiments were performed on at least five animals per group. Data are given as mean ⫾ SEM. * ⫽ P ⬍ .05.
Measurement of Renal Microcirculation Renal microcirculation was measured by surface laser Doppler probes (SP300, Oxford Optronics, Oxford, UK) connected to a flowmeter (Oxford Array, Oxford Optronics).
RESULTS
The animals received an intravenous infusion of CyA in the dosage of 1 mg/kg body weight. Thirty minutes after infusion renal microcirculation was significantly diminished (110 vs 90 LDF units, P ⬍ .05) (Fig 1). Simultaneous application of quinapril (0.1 mg/kg body weight) or losartan (2 mg/kg body weight) increased renal cortical microcirculation above control values (quinapril from 100 to 140 LDF units, P ⬍ .05; losartan from 110 to 155 LDF units, P ⬍ .05). Renal blood flow in CsA-treated animals was 7 mL/min vs
Continuous Measurement of Renal Blood Flow A midline abdominal incision was made, and the left kidney and the renal artery were freed from the surrounding fat and connective tissue by blunt dissection. The kidney was placed in a semicircular support. Transit-time flow probes (model 1RB, Transsonic Systems) filled with ultrasound coupling gel (Sonogel, Transsonic Systems) were positioned around the renal artery and connected to a two-channel small animal digital transit-time blood flowmeter (model T206, Transsonic).
From the Medizinische Klinik and Poliklinik, Universita¨tklinikum Mu¨nster, Mu¨nster, Germany. Supported by a grant from the German Ministery of Science and Education 01EC9801. Address reprint requests to U. Hillebrand, Medizinische Klinik and Poliklinik D, Universita¨tsklinikum Mu¨nster, Albert Schweitzer Str. 33, D-48129 Mu¨nster, Germany. E-mail: hohage@uni-muen ster.de
© 2002 by Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010
0041-1345/02/$–see front matter PII S0041-1345(02)03068-3
Transplantation Proceedings, 34, 1383–1384 (2002)
1383
1384
Fig 2. Renal blood flow after administration of vehicle, CsA, and combinations of CsA with quinapril or losartan on renal microcirculation. The experiments were performed on at least five animals per group. Data are given as mean ⫾ SEM. * ⫽ P ⬍ .05.
14 mL/min in control animals (Fig 2). Quinapril and losartan had no effect on renal blood flow alone. Simultaneous infusion of CsA and quinapril or CsA and losartan abolished both the negative effects of CsA on renal blood flow and the renal vascular resistance.
HILLEBRAND, KOBELT VOPHOVEN ET AL
is not completely understood. The fact that this decrease in GFR is rapidly reversible with removal of the drug suggests that hemodynamic factors play a critical role. Decreases in renal blood flow, significant increases in renal vascular resistance, and decreases in GFR have been reported after both acute and chronic administration of CsA in rats.4 Increased renal sympathetic nervous system activity may play a role in the renal hemodynamic alterations produced by CsA. Indeed, a marked increase in renal nerve activity after intravenous CsA administration has been reported. Renal denervation prevented the CsA-induced decrease in GFR noted in the intact kidneys. A protective effect was observed when rats were subjected to renal denervation or after administration of alpha receptor blocking agents.5,6 Increased peripheral renin activity has been reported in rats treated acutely or chronically with CsA.4, 7 The role of the angiotensin system in CsA-induced alterations in renal hemodynamics, however, is not clear. The results of the present study show that ACE inhibitors and angiotensin II receptor antagonists may prevent CsA-induced alterations of microcirculation and renal blood flow. A blood flow shift from the medulla toward the renal cortex may contribute at least in part to the increase of cortical microcirculation observed in animals treated with a combination of CsA and antihypertensive drugs. REFERENCES
DISCUSSION
The nephrotoxicity of CsA has been well documented in both humans and experimental models.1,3 The adverse effects of CsA on renal function include an acute, reversible, dose-dependent decrease in GFR; alterations in renal potassium handling; and a chronic, progressive interstitial fibrosis with irreversible renal damage. The mechanism of the acute reversible deterioration in GFR produced by CsA
1. Bennett WM: Int J Clin Pharmacol Ther 34:515, 1986 2. Perico N, Remuzzi G: Drugs 54:533, 1997 3. Morales JM, Andres A, Rengel M, et al: Nephrol Dial Transplant 16:121, 2001(suppl 4. Ajikobi DO, Novak P, Salevsky FC, et al: Ca J Physiol Pharmacol 74:964, 1996 5. Hohage H, Schlatter E, Greven J: Clin Nephrol 47:316, 1997 6. Hohage H, Hess K, Jahl C, et al: Clin Nephrol 48:346, 1997 7. Arendshorst WJ, Brannstrom K, Ruan X: J Am Soc Nephrol 10:149, 1999(suppl