大鼠异种原位肝移植急性排斥反应中一氧化氮合酶细胞定位的意义

目的　探讨一氧化氮合酶（ｃＮＯＳ,ｉＮＯＳ） 在金黄地鼠至大鼠异种原位肝移植急性排斥反应中的细胞定位及其意义．方法　我们应用金黄地鼠至大鼠异种原位肝移植急性排斥反应及大鼠同基因原位肝移植动物模型,应用ＮＡＤＰＨ 黄递酶组化染色及免疫组化染色观察移植肝组织ＮＯＳ 的活性及ｃＮＯＳ,ｉＮＯＳ 的蛋白表达．结果　大鼠异种原位肝移植急性排斥反应时血浆ＮＯ 代谢产物ＮＯ－ｘ 明显增高,环孢菌素Ａ 可显著抑制ＮＯ 的合成． 异种肝移植急性排斥反应时,ＮＡＤＰＨ＿ｄ 组化染色及其兔抗大鼠多克隆抗体ｉＮＯＳ,ｃＮＯＳ 免疫组化染色均呈强阳性表达,但以ｉＮＯＳ表达为主．ｉＮＯＳ 主要在肝细胞、肝窦内皮细胞及Ｋｕｐｆｆｅｒ 细胞等炎性细胞表达,而同基因组及免疫抑制治疗组则不表达．结论　原位肝移植肝细胞ＮＯ 产物可随移植肝的免疫状态不同而异,肝细胞ＮＯ 很可能具有重要的免疫保护作用,ＮＯ 合酶及其代谢产物ＮＯ－ｘ 在肝移植急性排斥反应中可具有早期的免疫学监测作用．     

输注同系鼠骨髓间充质干细胞对大鼠移植肝的抗排斥作用观察

目的观察输注与受体同系鼠骨髓间充质干细胞对大鼠移植肝脏的抗排斥作用。方法实验鼠随机分为A、B、C组。A组仅行DA-Lewis大鼠原位肝移植,B组行DA-Lewis大鼠原位肝移植术后予环孢素,C组行DA-Lewis大鼠原位肝移植同期输注Lewis大鼠骨髓间充质干细胞。结果术后C组血清ALT、AST、TBIL较A组显著降低（P均〈0.05）,与B组相近;B、C组IL-2、IL-4、IL-10和IFN-γ均升高（P均〈0.05）,但低于A组（P均〈0.05）;B、C组移植肝仅呈急性轻度排斥反应,A组呈急性重度排斥反应;B、C组生存时间长于A组（P均〈0.05）。结论大鼠肝移植后输注与受体同系鼠骨髓间充质干细胞能减轻移植肝的排斥反应。     

肝移植术后急性排斥反应患者血清GB mRNA的表达变化及意义

目的观察肝移植后发生急性排斥反应者外周血血清颗粒酶B（GB）mRNA表达变化，并探讨其意义。方法56例肝移植受者，其中46例未出现排斥反应（A组），10例出现急性排斥反应（B组）。采用SYBR荧光实时定量PCR法检测两组患者移植后30d内外周血清的GB mRNA。同时检测血清ALT、AST水平。结果B组患者出现排斥反应后外周血清GB mRNA与排斥前和A组患者相比均显著升高（P均〈0．01）。B组患者外周血清GB mRNA上升时间早于血肝功能酶ALT、AST升高2d。结论肝移植后出现急性排斥反应者外周血清的GB mRNA表达升高。GB mRNA可作为预测和诊断移植肝急性排斥反应的指标。     

Th17、Treg及其平衡与大鼠肝移植术后免疫耐受的研究

目的探讨肝移植术后肝组织T淋巴细胞Th17/Treg表达变化和肝移植免疫耐受之间的关系.方法以采用改良Kamada二袖套法建立LEWIS→BN原位肝移植大鼠急性排斥反应模型:LEWIS大鼠为供体,BN大鼠为受体,行原位肝移植(orthotopic liver transplantation,OLT).对照组为:BN→BN原位肝移植大鼠耐受模型:BN大鼠为供体,BN大鼠为受体,行OLT.术后观察大鼠一般情况,并于第1、3、5及7天分别处死大鼠取肝组织,HE染色观察肝组织结构.检测血清谷丙转氨酶(alanine transaminase,ALT)、谷草转氨酶(aspartate transaminase,AST)、白介素(interleukin,IL)-17、IL-23、IL-10和转化生长因子-β1(transforming growth factor beta 1,TGF-β1)的表达水平.结果与对照组比较,LEWIS→BN组各时间点肝功能指标ALT、AS T明显上调(P0.05).对照组第7天ALT:819.29 IU/L±79.33 IU/L;OLT组第7天ALT:1305.62 IU/L±94.82 IU/L;对照组第7天AST:337.82 IU/L±32.17 IU/L;OLT组第7天AST:867.75 IU/L±73.97 IU/L;大鼠第7天外周血Th17相关因子IL-17(对照组:28.67 pg/m L±2.55 pg/m L,OLT组:92.36 pg/m L±9.00 pg/m L)、IL-23(对照组:26.82 pg/m L±8.17 pg/m L,OLT组:62.98 pg/m L±12.96 pg/m L)明显上升,而Treg相关因子IL-10(对照组:76.92 pg/m L±12.87 pg/m L,OLT组:47.92 pg/m L±7.00 pg/m L)、TGF-β1(对照组:129.47 pg/m L±18.37 pg/m L,OLT组:82.48 pg/m L±11.83 pg/m L)明显下降,Th17/Treg表达失去平衡.同时,TGF-β下游Smad2/3蛋白具有跟TGF-β1相同变化趋势,LEWIS→BN急性排斥组与BN→BN免疫耐受组相比,差异具有统计意义(P0.05).结论IL-17、IL-23、IL-10、TGF-β1、Smad2/3参与了同种异体大鼠肝移植急性排斥反应,引起Treg向Th17的免疫偏移,可作为治疗大鼠肝移植免疫耐受的靶向指标.     

透明质酸在大鼠肝移植中的应用

1原文的要点 作者应用不同品系的大鼠进行原位肝移植[1],在肝移植术后不同时间用放免法检测血中透明质酸(HA)的浓度.比较正常组、同基因移植组、异基因移植组以及异基因移植+环孢酶素A(CsA)组间透明质酸变化的差异,以及各组转氨酶(ALT)和总胆红素(Bilirubin)的变化情况.结果表明肝移植后血清HA水平与正常组比较有明显升高(P＜0.01);而术后6 d排斥反应组HA水平明显高于同基因移植组和异基因移植+CsA组(P＜0.01);ALT和Bilirubin在术后9 d才出现明显差异.作者认为由于急性排斥反应造成肝内皮细胞的损伤,导致HA水平在术后6 d时高于其他处理组;连续测定肝移植术后的HA水平有助于排斥反应的早期诊断.本文立题新颖,构思独特,实验设计比较合理,放免法检测HA浓度特异性强,检测血中HA水平反映移植排斥反应的研究在国内还没有发现有相关报道.就原文内容提出几点商榷意见:①实验动物品系不纯,SD大鼠以及Wistar大鼠属于封闭群,个体之间差异较大,如能够用近交系大鼠则更具有说服力.②内源性HA水平与冷缺血保存及再灌注损伤等因素关系密切,在术后数小时至数天内便恢复正常.     

肝移植术后急性排斥反应中Th1/Th2变化的研究

目的探讨肝移植术后患者Th1/Th2在急性排斥反应中的变化及意义。方法采用双色流式细胞术分析21例肝移植患者手术前后外周血中的Th1细胞和Th2细胞的百分率,并计算Th1/Th2的变化。结果肝移植术后急性排斥过程中Th1细胞较术前有显著性升高,Th2细胞较术前无显著性变化,Th1/Th2较术前有显著性升高。排斥组与非排斥组相比,Th1/Th2有显著性升高。急性排斥时及排斥前Th1/Th2与术前相比有显著性差异。结论Th1/Th2的变化与肝移植急性排斥反应的发生密切相关。术后监测外周血中Th1/Th2是进行免疫监测及指导免疫抑制剂应用的简便有效的方法     

供体凋亡细胞预输注抑制肝移植急性排斥反应的实验研究

目的探讨供体凋亡细胞预输注抑制肝移植急性排斥反应的效果及机制。方法无菌取SD大鼠脾脏,分别采用光照法和水浴法制备凋亡细胞和坏死细胞,并经流式细胞仪检测证实。将sD（供体）、Wistar（受体）大鼠各40只随机分为A组12例、B组14例、C组14例,分别经阴茎背静脉注射生理盐水1ml、坏死细胞1×10^7个、凋亡细胞1×10^7个,至第7天参照Kamada法行原位肝移植术。观察三组围术期一般情况;术后第4天各组均取外周血检测肝功能指标ALT、AST、TBIL及血清IL-2、IL-10水平;术后第4天各组分别处死3只大鼠,取肝组织行病理学检查,判断急性排斥分级,取石蜡切片检测凋亡指数;分别取SD及F344大鼠脾淋巴细胞与Wistar大鼠脾淋巴细胞混合培养,测定淋巴细胞转化率。结果C组存活期明显长于A、B组,术后肝功能、病理改变及肝细胞凋亡指数均优于A、B组,淋巴细胞转化率显著低于A、B组。结论术前预输注供体特异性凋亡细胞可通过诱导供体特异性免疫耐受抑制大鼠肝移植术后急性排斥反应,改善移植肝功能,延长存活时间。     

细胞凋亡调控基因bcl-2、bax在同种异体肢体移植急性排斥反应中的表达

目的探讨细胞凋亡调控基因bcl-2、bax表达在同种异体肢体移植急性排斥反应时的作用及其意义。方法选用近交系SD大鼠、Wistar大鼠进行同种异体肢体移植。实验组:异基因(SD→Wistar);对照组:同基因(Wistar→Wistar)。于术后第1、3、5、7天分别取移植肢体皮肤、肌肉组织进行病理学观察。原位末端标记法(TUNEL)和免疫组化方法检测移植肢体中的凋亡细胞及bcl-2、bax表达的变化。结果病理学检查结果显示实验组大鼠在术后发生由轻到重的急性排斥反应,术后第7天因严重排斥而使小血管广泛栓塞。对照组无明显排斥现象。实验组的细胞凋亡数明显高于对照组,同时bcl-2表达降低,bax表达增高。结论细胞凋亡在大鼠异基因肢体移植急性排斥反应中发挥重要作用,调控基因bcl-2、bax可作为判断移植肢体预后及监测排斥反应的重要指标。     

穿孔素及颗粒酶B在肝移植排斥反应中的表达及意义

目的检测穿孔素和颗粒酶B在肝移植术后排斥反应中的表达情况，以评价其作为肝移植术后排斥反应的早期诊断指标价值。方法收集35个肝移植术后肝穿刺标本，应用免疫组织化学方法检测穿孔素和颗粒酶B表达，并与病理组织学结果相比较，研究其表达与急性排斥反应的关系。结果在35个标本中，19个经病理组织学诊断为排斥反应，其中急性排斥17例次，慢性排斥2例次。其中穿孔素和颗粒酶B在排斥反应者中的表达阳性率分别为100％(19／19)和94．7％(18／19)。而在未发生排斥反应者中，其表达阳性率分别为25．0％(4／16)和12．5％(2／16)。穿孔素及颗粒酶B多呈同步表达，仅3个标本为仅有穿孔素表达而无颗粒酶B表达，未观察到仅有颗粒酶B表达而无穿孔素表达。穿孔素和颗粒酶B的阳性表达与移植肝急性排斥反应的发生密切相关。结论穿孔素和颗粒酶B参与了肝移植后排斥反应的发生，其表达可作为术后急性排斥反应的辅助诊断指标。     

大黄酸对肝移植大鼠急性排斥反应的影响

目的 探讨大黄酸对肝移植大鼠急性排斥反应的影响。方法 采用改良“二袖套法”建立60只DA→Lewis大鼠原位肝移植模型并随机分为对照组、环孢素组及大黄酸组各20只。对照组予生理盐水2 m L/d灌胃,环孢素组予环孢素A 10 mg/（kg·d）腹腔注射,大黄酸组予大黄酸20 mg/（kg·d）口服。连续干预7 d后每组各处死大鼠10只,取腔静脉血,采用连续监测法检测血清ALT、AST、LDH水平,ELISA法测血清TNF-α、IL-2、IFN-γ等细胞因子水平;观察肝脏病变情况,计算肝组织排斥活动指数（RAI）。记录各组未处死大鼠的生存期。结果 术后1周,环孢素组及大黄酸组血清ALT、AST、LDH、TNF-α、IL-2和IFN-γ水平均低于对照组（P均〈0.05）。对照组肝组织标本均呈现重度排斥反应;环孢素组及大黄酸组分别有3、4例标本呈重度排斥反应,余均为中度排斥反应。环孢素组、大黄酸组RAI均明显低于对照组（P均〈0.05）;术后环孢素组及大黄酸组存活期长于对照组（P均〈0.05）。结论 大黄酸可减轻大鼠肝移植急性排斥反应,延长大鼠生存期,效果与环孢素A相近。     

他克莫司治疗移植肾慢性排斥的初步临床观察

目的：探讨他克莫司（FK506）、环孢素A（CsA)治疗移植肾慢性排斥（CR)的可行性及安全性。方法：40例同种异体肾移植患者肾功能减退经病理证实为CR，随机分为CsA切我为FK506组20例、继续使用CsA组20例。观察各组移植肾功能、肾小球滤过率、蛋白尿、血压、血脂变化及急性排斥（AR）发生率，治疗后随访12个月。结果：追踪12个月，FK506组16例移植肾功能稳定（80％）；3例行血液透析治疗，1例死亡，人存活率95％。CsA组15例移植肾功能稳定，3例行血液透析治疗，逆转成功率75％；2例死亡，人存活率90％。结论：FK506可以延缓慢性移植物失功。FK506的使用是安全和有效的。     

Optimal immunosuppressor induces stable gut microbiota after liver transplantation

AIM To study the influence of different doses of tacrolimus(FK506)on gut microbiota after liver transplantation(LT)in rats.METHODS Specific pathogen-free Brown Norway(BN)rats and Lewis rats were separated into five groups:(1)Tolerance group(BN-BN LT,n=8);(2)rejection group(Lewis-BN LT,n=8);(3)high dosage FK506(FK506-H)group(Lewis-BN LT,n=8);(4)middle dosage FK506(FK506-M)group(Lewis-BN LT,n=8);and(5)low dosage FK506(FK506-L)group(LewisBN LT,n=8).FK506 was administered to recipients at a dose of 1.0 mg/kg,0.5 mg/kg,and 0.1 mg/kg body weight for 29 d after LT to the FK506-H,FK506-M,and FK506-L groups,respectively.On the 30~(th) day after LT,all rats were sampled and euthanized.Blood samples were harvested for liver function and plasma endotoxin testing.Hepatic graft and ileocecal tissues were collected for histopathology observation.Ileocecal contents were used for DNA extraction,Real-time quantitative polymerase chain reaction(RT-PCR)and digital processing of denaturing gradient gel electrophoresis(DGGE)profiles and analysis.RESULTS Compared to the FK506-H and FK506-L groups,FK506-M was optimal for maintaining immunosuppression and inducing normal graft function;the FK506-M maintained gut barrier integrity and low plasma endotoxin levels;furthermore,DGGE results showed that FK506-M induced stable gut microbiota.Diversity analysis indicated that FK506-M increased species richness and rare species abundance,and cluster analysis confirmed the stable gut microbiota induced by FK506-M.Phylogenetic tree analysis identified crucial bacteria associated with FK506-M;seven of the nine bacteria that were decreased corresponded to Bacteroidetes,while increased bacteria were of the Bifidobacterium species.FK506-M increased Faecalibacterium prausnitzii and Bifidobacterium spp.and decreased Bacteroides-Prevotella and Enterobacteriaceae,as assessed by RT-PCR,which confirmed the crucial bacterial alterations identified through DGGE.CONCLUSION Compared to the low or high dosage of FK506,an optimal dosage of FK506 induced immunosuppression,normal graft function and stable gut microbiota following LT in rats.The stable gut microbiota presented increased probiotics and decreased potential pathogenic endotoxin-producing bacteria.These findings provide a novel strategy based on gut microbiota for immunosuppressive dosage assessment for recipients following LT.     

FK506 inhibits human lymphocyte migration and the production of lymphocyte chemotactic factors in liver allograft recipients

The macroglide immunosuppressant FK506 is effective at preventing and reversing hepatic allograft rejection. The establishment of graft rejection is dependent upon an influx of lymphocytes from the circulation into the graft in response to locally secreted chemotactic factors. Thus, inhibition of lymphocyte migration might be an additional mode of action of FK506 that could block lymphocyte recruitment to rejecting liver allografts. In the present study, we provide evidence to support this hypothesis because we have demonstrated, using in vitro migration assays, that FK506 can inhibit the migration of lymphocytes, including CD4+ and CD8+ T-cells, to structurally diverse chemotactic factors that are present during human liver allograft rejection. In addition, FK506 acts on lymphocytes in patients with graft rejection to inhibit migration and to block the secretion of chemotactic factors in vitro. Thus, FK506 might reverse established graft rejection by inhibiting lymphocyte recruitment to the graft in vivo. (Hepatology 1996 Jun;23(6):1476-83)     

Peroxynitrite formation during rat hepatic allograft rejection

The role of nitric oxide (NO) on tissue injury of hepatic allografts during rejection remains controversial. We investigated inducible nitric oxide synthase (iNOS) expression and formation of peroxynitrite in ACI rat liver grafts implanted in recipients. Animals were divided into four experimental groups: group I, isografts; group II, untreated hepatic allografts; group III, allografts treated with FK506; and group IV, allografts pretreated with donor-specific blood transfusion (DST). Serum nitrite/nitrate, interferon-gamma (IFN-gamma), and tumor necrosis factor-alpha (TNF-alpha) concentrations increased significantly in group II rats after transplantation but were significantly lower in groups I, III, and IV. The numbers of macrophages that reacted with an antimacrophage iNOS monoclonal antibody as well as iNOS messenger RNA (mRNA) levels in liver specimens were also much lower in groups I, III, and IV as compared with group II. Immunostaining and Western blot analysis showed prominent tissue nitrotyrosine expression in untreated hepatic allografts, but not in allografts treated with FK506 or donor-specific blood. These results suggest that one of the mechanisms by which production of NO results in injury in rat hepatic allografts may be because of its reaction with superoxide to form peroxynitrite.     

Pretreatment with FK506 up-regulates insulin receptors in regenerating rat liver

This report examines the effect of FK506 pretreatment on liver insulin receptor expression in partially (70%) hepatectomized rats. FK506 pretreatment led to an increased insulin receptor number 24 hours after hepatectomy, detected by means of insulin binding and cross-linking procedures. This increase was related to enhanced insulin receptor expression determined by in vitro mRNA translation and Western blot techniques. We also tested the functionality of the expressed insulin receptors by [(3)H] thymidine incorporation into DNA in insulin-stimulated hepatocytes. The results show that FK506 pretreatment elicits an increase in the amount of insulin receptor alpha-subunits as measured by Western blot. Maximum alpha-subunit expression recorded 24 hours after surgery was preceded by increased insulin receptor mRNA levels, which were detected 6 hours after hepatectomy. Moreover, in FK506-pretreated rat hepatocytes, obtained from remnant livers 24 hours after partial hepatectomy (PH), the increase in insulin receptor number was associated with improved sensitivity to the hormone. However, in both experimental groups (FK506-pretreated and nonpretreated rats), the sensitivity of hepatocytes toward epidermal growth factor (EGF) showed no significant change, which suggests a specific effect of FK506 on insulin receptor expression. In conclusion, our findings suggest that FK506 pretreatment induces insulin receptor expression in regenerating rat liver and promotes liver regeneration in hepatectomized rats.     

FK506 promotes liver regeneration by suppressing natural killer cell activity

We examined the mechanism of promotion of liver regeneration by tacrolimus hydrate (FK506), a potent immunosuppressant, after partial hepatectomy. The administration of FK506 significantly increased the bromodeoxyuridine (BrdU) labelling index at 36 and 48 h after 70% hepatectomy compared with the placebo group. Using the same model, we examined the effect of FK506 on the expression of hepatocyte growth factor (HGF) and transforming growth factor-β1 (TGF-β1) and found no changes in HGF and TGF-β1 mRNA expression in the liver or in the HGF protein concentration in plasma. We found that pretreatment with FK506 markedly reduced the activity and number of liver-resident natural killer (NK) cells at the time of partial hepatectomy. Our observations suggest that the promotion of liver regeneration by FK506 may be attributable to a reduction in the number of liver-resident NK cells and to inhibition of their activity.     

Evidence for impaired glucose effectiveness in cirrhotic patients after liver transplantation

To evaluate the impact of acute and chronic liver disease and single immunosuppression (cyclosporine A [CSA] or FK506) on insulin sensitivity and glucose effectiveness in liver-grafted patients, we performed a frequently sampled intravenous glucose tolerance test (FSIGTT) in nondiabetic patients after orthotopic liver transplantation (OLT) with acute liver failure ([ALF] group, n = 9, with CSA therapy), in patients after OLT with chronic liver disease (CSA group, n = 8; FK506 group, n = 8), and in 9 healthy control subjects. Insulin sensitivity and glucose effectiveness were determined by analyzing glucose and insulin data from the FSIGTT with Bergman's minimal model technique for glucose. The intravenous glucose tolerance index ([KG] ie, the slope of the regression of the logarithm of blood glucose concentration) was not different between the ALF group (2.17 +/- 0.16 min(-1)) and controls (2.29 +/- 0.13 min(-1)), but was lower (P < .05) in both groups with chronic liver disease (CSA group, 1.46 +/- 0.1; FK506 group, 1.61 +/- 0.11 min(-1)) compared with the ALF group (P < .05). A positive relation for the KG and glucose effectiveness was found in all liver-grafted patients and controls. Insulin sensitivity was not different between all liver-grafted patients and controls. The body mass index (BMI) was the overall determinant of insulin sensitivity in all groups. Single immunosuppressive therapy does not impair insulin sensitivity in liver-grafted patients. The lower glucose effectiveness in liver-grafted patients with chronic liver disease but not in patients after ALF points to a defect in the regulation of glucose-mediated glucose uptake in peripheral tissue.     

FK506 attenuates developing and established joint inflammation and suppresses interleukin 6 and nitric oxide expression in bacterial cell wall induced polyarthritis

OBJECTIVE: To determine the efficacy of therapeutic administration of FK506 (Tacrolimus) in suppressing developing and established joint inflammation, proinflammatory cytokine expression, and nitric oxide (NO) production in peptidoglycan-polysaccharide (PG/PS) induced experimental polyarthritis in rats. METHODS: Chronic joint inflammation was induced by intraperitoneal injection of PG/PS, and joint inflammation was quantified using arthritis index and paw volume. Serum and joint levels of interleukin 6 (IL-6) were measured by bioassay and Western blot analysis respectively, and serum levels of NO production were determined by the Griess procedure and the expression of the inducible isoform of nitric oxide synthase (i-NOS) in the joints was determined by Western blot analysis. RESULTS: Arthritis induced by PG/PS is biphasic, progressing through an initial acute phase and a remission phase, which is followed by a persistent chronic phase. Daily administration of FK506 initiated during the remission phase significantly attenuated the onset and development of chronic joint inflammation. We observed a significant reduction in joint inflammation and swelling, an apparent suppression of pannus development, and minimal erosive damage to the articular cartilage and subchondral bone. Fully established chronic joint inflammation was also ameliorated by daily administration of FK506. Joint swelling and inflammation was significantly reduced by 5 days post-treatment with FK506 and the erosive activity associated with the pannus appeared diminished. The elevated expression of IL-6 and NO characteristic of chronic joint inflammation in the serum and in joint tissue was significantly reduced by FK506 treatment. CONCLUSION: Therapeutic administration of FK506 has a profound antiinflammatory effect on the development of the chronic, erosive arthritis induced by PG/PS. This attenuation in joint inflammation was associated with suppression of IL-6 and NO production systemically and locally in the joints. Our data suggest that FK506 may be effective in the treatment of chronic joint inflammation associated with rheumatoid arthritis.     

Chronic Treatment with FK506 Increases p70 S6 Kinase Activity Associated with Reduced Nitric Oxide Synthase Activity in Rabbit Hearts

FK506, an immunosuppressant, modulates phosphorylation of nitric oxide (NO) synthase, and induces cardiac hypertrophy in clinical settings. Having recently reported that chronic treatment with an inhibitor of NO synthase induces cardiac hypertrophy associated with the activation of 70-kD S6 kinase (p70^S6K), which plays an important role in cardiac hypertrophy by regulating protein synthesis, we investigated the effects of chronic administration of FK506 on NO synthase and p70^S6K activities in hearts. Twenty rabbits were divided into four groups: untreated rabbits, those treated with low-dose FK506 (0.10 mg/kg), those treated with medium-dose FK506 (0.20 mg/kg), and those treated with high-dose FK506 (0.40 mg/kg). FK506 was administered intravenously twice a day. After 4 weeks of treatment with FK506, calcium-dependent NO synthase activity in myocardium in the high-dose FK506 group was lower (P < 0.05) than in the untreated group. p70^S6K activity in myocardium in the high-dose group was higher (P < 0.05) than in the untreated group. There was a significant (P < 0.05) inverse correlation between NO synthase and p70^S6K activities in myocardium. However, the endothelial-dependent vasodilation of aortic rings or plasma levels of NO metabolites during experimental protocols did not differ among the groups studied. These findings suggest that chronic treatment of FK506 activates p70^S6K and reduces NO synthase activity in rabbit hearts. Reduced NO synthase and/or activated p70^S6K activities in hearts might contribute to the cardiac hypertrophy observed in some patients receiving FK506.