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The renin-angiotensin system (RAS) is a key regulator of vascular tone and blood pressure. In addition, angiotensin II also has a number of cellular effects that may contribute to disease pathogenesis. Using Agtr1a(-/-) mice, which lack AT(1A) receptors for angiotensin II, we have identified a novel function of the RAS to modulate the immune system. We find that angiotensin II, acting through type 1 (AT(1)) receptors on immune cells, triggers the proliferation of splenic lymphocytes. These actions contribute to the vigor of cellular alloimmune responses. Within lymphoid organs, sufficient components of the RAS are present to activate AT(1) receptors during an immune response, promoting cell growth. These actions require activation of calcineurin phosphatase. In an in vivo model of cardiac transplantation, the absence of AT(1) signaling accentuates the immunosuppressive effects of the calcineurin inhibitor cyclosporine. We conclude that inhibition of AT(1) receptor signaling should be useful as an anti-inflammatory and immunosuppressive therapy. Furthermore, the actions of the RAS to promote lymphocyte activation may contribute to inflammation that characterizes a number of diseases of the heart and the vascular system.

We previously reported that heart transplant patients given cyclosporine for more than 2 years (short-term evaluation) had severe renal lesions and markedly reduced glomerular filtration rate and renal plasma flow (Kidney Int 40:243-250, 1991). We report the analysis of renal function in the same patients after 3 additional years of follow-up (long-term evaluation) while they continued to take cyclosporine. Since the previous evaluation, the dose of cyclosporine was adjusted to maintain stable trough levels and antihypertensive therapy was unchanged. The mean time-averaged dose of cyclosporine during the follow-up was 4.5 +/- 2.1 mg/kg/d. The systolic blood pressure at long-term evaluation (146 +/- 16 mm Hg) was increased (P < 0.05) compared with that at short-term evaluation (140 +/- 13 mm Hg), whereas diastolic blood pressure (long-term 91 +/- 9 mm Hg v short-term 88 +/- 9 mm Hg) and mean blood pressure (long-term 110 +/- 12 mm Hg v short-term 108 +/- 11 mm Hg) did not change significantly. Serum creatinine concentrations at long-term (1.7 +/- 0.3 mg/dL) and at short-term (1.7 +/- 0.4 mg/dL) evaluations were similar. At long-term evaluation the renal plasma flow (300 +/- 64 mL/min/1.73 m2) was not decreased compared with that at short-term evaluation (325 +/- 94 mL/min/1.73 m2), while the glomerular filtration rate increased significantly (43 +/- 15 mL/min/1.73 m2 v 36 +/- 8 mL/min/1.73 m2, respectively; P < 0.05). None of the patients became proteinuric after short-term evaluation; in those patients who were already proteinuric, urinary protein excretion did not increase over time.(ABSTRACT TRUNCATED AT 250 WORDS)

We studied the potential renoprotective properties of a calcium channel blocker in moderately hyperglycemic diabetic rats both in the early phase of the disease and in the very long term, and compared such an effect with that of an angiotensin-I-converting enzyme (ACE) inhibitor. Three groups of diabetic rats, one receiving no therapy except insulin and the remaining two receiving insulin and the ACE inhibitor enalapril or the calcium blocker lacidipine and one group of nondiabetic control rats were followed for 4-6 weeks. Both antihypertensive drugs lowered systolic blood pressure comparably. At the end of the observation period, untreated diabetic rats exhibited elevation of glomerular filtration rate and renal plasma flow. Both enalapril and lacidipine treatment completely prevented whole-kidney hyperfiltration and hyperperfusion. Four additional groups of rats, similarly treated, were followed for 1 year. A comparable control of systolic blood pressure and blood glucose level was achieved with the two antihypertensive regimens throughout the whole study period. At 12 months, the average kidney weight was elevated to similar values in all diabetic groups relative to control rats. Untreated diabetic rats had progressive proteinuria and developed glomerulosclerosis. Enalapril markedly limited the development of proteinuria. By contrast, urinary protein excretion in diabetic rats given lacidipine markedly increased with time, and values were as high as those in untreated diabetic animals. Similarly, only enalapril was effective in limiting glomerular injury. These results indicate that ACE inhibition but not calcium channel blockade has a favorable effect in preventing renal disease progression in diabetic rats and suggest that the various antihypertensive regimens are not equally beneficial in protecting against diabetic glomerulopathy.

Renal toxicity, possibly due to vasoconstriction and vascular injury, is the most relevant side-effect of chronic cyclosporine (CsA) therapy given to prevent graft rejection. In kidney transplant recipients each oral dose of CsA is invariably followed by a transient reduction in renal plasma flow (RPF) and glomerular filtration rate (GFR) that results from a form of acute reversible hypoperfusion. We sought to determine whether the Ca2+ channel blocker, lacidipine, prevented CsA-associated renal hypoperfusion in these patients. Parallel studies on CsA pharmacokinetics, renal function parameters (GFR and RPF), as inulin and p-aminohippurate (PAH) clearances, respectively, and urinary excretion of the vasoconstrictor endothelin in 10 consecutive renal transplant patients given CsA as a part of their immunosuppressive therapy were performed. Patients were studied at different time intervals after CsA alone, CsA and lacidipine (4 mg/day), and again seven days after lacidipine withdrawal. In all patients basal RPF and GFR declined on average 51% (139.3 +/- 20.7 ml/min/1.73 m2) and 50% (32.5 +/- 5.8 ml/min/1.73 m2), respectively, two to four hours after maximum blood CsA concentration was reached. As blood levels of CsA returned to trough, both parameters progressively increased to baseline. Lacidipine administration completely prevented the fall in RPF (pre-CsA: 277.1 +/- 23.6; 6 hr post-CsA: 304.5 +/- 31.1 ml/min/1.73 m2) and GFR (pre-CsA: 66.6 +/- 8.1; 6 hr post-CsA: 70.1 +/- 9.8 ml/min/1.73 m2). When lacidipine treatment was discontinued the abnormal RPF and GFR response to CsA administration was again observed.(ABSTRACT TRUNCATED AT 250 WORDS)

We have previously documented that cyclosporine exerts a direct cytotoxic effect on endothelial cells and causes an increase in renal vascular resistance (RVR) in the rat. In the present study we investigated whether FK506, a novel immunosuppressive agent thought to be less nephrotoxic than CsA, impairs endothelial cell function in vitro and affects RVR in vivo. In vitro eicosanoid release and endothelin release were measured in bovine aortic endothelial cells in culture exposed for 1, 6, and 24 hr to increasing concentrations of FK506 (1 nM to 10 microM) or CsA (0.5, 10 microM). No significant changes in TxB2 and 6-keto-PGF1 alpha (the stable breakdown products of TxA2 and PGI2, respectively) and endothelin release were found after 1 and 6 hr of incubation with all the concentrations of FK506 and CsA considered. FK506 did not affect endothelin release even after 24 hr of incubation. In contrast, cell exposure to CsA was associated with a dose-dependent increase in TxB2, 6-keto-PGF1 alpha, and endothelin release that reached statistical significance after incubation with 10 microM CsA. FK506 did not induce cell detachment or lysis at any concentration and time considered, while 10 microM CsA induced a significant reduction in cell count accompanied by cell lysis. In vivo studies showed that a single i.v. injection of FK506 to rats within a broad range of doses (28 ng/kg to 2.8 micrograms/kg) did not modify RVR. This was true even for a dose as high as 20 mg/kg, while 20 mg/kg CsA caused a dramatic increase in RVR. We conclude that FK506, unlike CsA, does not induce endothelial cell injury in vitro. Whether this explains the differences in renovascular resistance observed in vivo after acute injection of FK506 and CsA is an attractive possibility that needs to be further explored.

A variety of side effects are associated with the use of cyclosporine, the most relevant of which remains the renal toxicity. We did parallel studies on cyclosporine pharmacokinetics and renal function in patients who had a recent kidney transplant and were given cyclosporine as a part of their immunosuppressive therapy. Seven consecutive renal transplant patients were studied at the end of a month of treatment while on different oral cyclosporine doses (5, 3.5, 2.5, or 1.5 mg/kg, twice a day, respectively). Cyclosporine pharmacokinetics profiles and renal function parameters (GFR and renal plasma flow [RPF], as inulin and p-amino hippurate clearances, respectively) were determined before and over a 12-hr period after each single dose of cyclosporine. Plasma levels and urinary excretion rate of endothelin were also studied before and after the highest cyclosporine dose (5 mg/kg). Mean trough levels, area under the curve values, and maximum concentration of blood cyclosporine were comparable after 5 and 3.5 mg/kg cyclosporine and decreased in a dose-dependent manner after the lower doses (2.5 and 1.5 mg/kg). In the same patients GFR declined on average 63%, 53%, 35%, and 18%, 2-4 hr after maximum cyclosporine concentration was reached. As blood levels of cyclosporine returned to trough, GFR progressively increased to baseline. Similar results were found for RPF; 5 mg/kg cyclosporine did not modify endothelin plasma levels. By contrast, urinary excretion of the peptide increased significantly (P less than 0.01) in the 6 hr that followed cyclosporine administration and returned within the normal range in the subsequent 6 hr. Following each oral administration of cyclosporine, 2-4 hr after peak blood concentration was reached, patients showed renal hypoperfusion, transient and rapidly reversible. This was associated with an increased urinary endothelin excretion rate that was also transient. It is speculated that an excessive renal synthesis of endothelin is the cause of the daily renal hypoperfusion observed in patients with renal transplants given cyclosporine.