An Examination of Pregnancy Cases After Kidney Transplantation: Single-Center Experience

INTRODUCTION

The number of young women who wish to become pregnant opting for kidney transplants is increasing, as becoming pregnant under hemodialysis or peritoneal dialysis is associated with many risks. However, there have been reports indicating that these patients are subject to a higher risk of miscarriage compared to women with normal renal function. We examine and report cases of patients that experienced pregnancy after undergoing kidney transplantation at our hospital.

SUBJECTS AND METHOD

Of the kidney transplantation cases that were performed at our hospital between 1985 and 2016, there were 7 cases of pregnancy. The serum creatinine levels, urine protein findings, etc, of these 7 cases were examined during the pre-pregnancy, pregnancy, childbirth, and postpartum periods.

RESULTS

All 7 cases were able to give birth. There were two cases of transient postpartum hypertension. There were no cases of obvious pregnancy toxemia or fetal growth retardation. Two of the cases resulted in the failure of the transplanted kidneys.

DISCUSSION

According to previous studies on pregnancy and childbirth after kidney transplantation, the presence of high blood pressure and proteinuria as well as the renal function at the time of pregnancy is closely associated with postpartum renal function. Urine protein was detected prior to pregnancy in both cases and resulted in the failure of the transplanted kidneys. The influence of immunosuppressants on the mother and fetus is also an important consideration.

CONCLUSION

We believe it is extremely important to ensure a thorough informed consent process prior to pregnancy and systematic use of immunosuppressants for young female transplant recipients.

Prophylactic use of intravenous prostaglandin E1 for radial arterial spasm in uremic patients undergoing construction of arteriovenous hemodialysis fistulas

Radial arterial spasm in uremic patients undergoing construction of internal arteriovenous (AV) dialysis fistulas was investigated transcutaneously using ultrasonic Doppler flowmetry. In 6 of 16 control patients, the radial arterial blood flow was significantly decreased for 20 min after anastomosing, indicating vasospasm. Vasospasm did not occur in 15 patients who were continuously administered prostaglandin E1 (PGE1) intravenously (10 ng/kg/min) during surgery. The arterial blood flow was significantly increased in patients receiving PGE1 in comparison with control patients not receiving PGE1 and in whom vasospasm did not occur. Regarding patency of hemodialysis access, the fistula was obstructed in one control patient with radial arterial spasm, but not in patients with PGE1 infusion. Our study suggests that PGE1 may be effective in preventing vasospasm in patients undergoing placement of internal AV dialysis fistulas.

Clinical Outcomes and Results of Pathological Findings of 1-year Protocol Biopsy in Recipients of ABO-Incompatible Living Donor Kidney Transplantants

OBJECTIVES

ABO-incompatible kidney transplantation has increased the possibility of finding suitable living donors for patients with renal failure. However, there are inevitable immunological risks, including a high risk of early post-transplantation complications. The purpose of this study was to evaluate recipient outcomes following ABO-incompatible kidney transplantation.

METHODS

Seventy-one patients who had undergone living-donor kidney transplantation (LDKT) at our center between January 2008 and December 2013 were divided into ABO-incompatible (ABOi; n = 21) and ABO-compatible (ABOc; n = 50) groups. Baseline data, graft function, immunosuppressant use, and the results of biopsy 1 year after LDKT were compared between the groups.

RESULTS

Recipient preemptive LDKT rates were significantly different between groups (P = .017). Graft function, incidence of infection, and rates of T-cell-mediated rejection and borderline changes requiring medication were not significantly different. There was no acute antibody-mediated rejection. Selectivity of the immunosuppressant, tacrolimus, was significantly different between groups (P < .01); however, steroid withdrawal rates, mycophenolate mofetil doses, and calcineurin inhibitor trough levels were not different. Regarding biopsy data, interstitial fibrosis scores were significantly different between groups (P = .011), as were interstitial fibrosis and tubular atrophy scores (P = .045) and arteriolar hyalinosis score (P = .022).

CONCLUSION

ABOi LDKT was relatively safe, with no significant difference in the incidence of rejection compared to ABOc LDKT. Managing chronic pathological changes and arteriolar hyalinosis prophylaxis after ABOi LDKT may result in more successful outcomes.

A Novel Assessment of Vascular Regions Using an Intraoperative Near-Infrared Fluorescence

INTRODUCTION

The risk of complications and transplant renal function increases in multiple arterial renal transplantations compared with single arterial renal transplantations. Even when multiple arteries are involved, with the introduction of laparoscopic nephrectomy, I mainly choose the left side kidney. Therefore, the number of renal artery reconstructions is increasing, and simultaneous imaging of arterial rebuilding during the donor nephrectomy is important.

MATERIAL

Between 2006 and 2015, we performed 132 living donor kidney transplantations at our center and analyzed 32 cases that were diagnosed pre- and intraoperatively.

METHOD

We compared the single renal artery (SRA) and multiple renal arteries (MRA) groups and analyzed the number of renal arteries, reconstruction methods, donor and recipient ages, sex, total ischemic times, and 1-month serum creatinine values.

RESULT

In the MRA and SRA groups, the average recipient age was 52.3 and 47.0 years, respectively, while the average donor age was 52.9 and 53.1 years, respectively. In SRA and MRA groups, total ischemic time (TIT) was 96.1 and 143.6 min (P < .01). Serum creatinine level 1 month post-transplantation was 1.54 and 1.25, respectively (P < .001). Here we experienced 12 cases of living renal donor nephrectomy with multiple vessels in which the vascular supply territory was first assessed in April 2013 using an intraoperative near-infrared fluorescence camera system. In addition, regarding TIT, it is possible to shorten surgery by using individual anastomosis and ligation.

CONCLUSION

By managing multiple donors; arteries by nephrectomy, it is possible to improve kidney transplantation results.

Formal nucleophilic borylation and borylative cyclization of organic halides

Recent advances in borylations of organic halides, including both transition-metal-catalyzed and metal-free methods are summarized. Borylative cyclization is also discussed.

Postoperative Compensatory Changes and Blood Flow Parameter of the Preserved Kidney in Elderly Living Related Donors Evaluated by Doppler Ultrasonography

INTRODUCTION

Elderly kidney donors have recently become more common in living related kidney transplantation in Japan. Therefore, it is important to evaluate whether kidney function in elderly donors after nephrectomy is preserved over long periods of time. Doppler ultrasonography measurement is practical for donors after nephrectomy because it involves simple and noninvasive examinations. Doppler ultrasonography can detect compensatory hypertrophy and blood flow parameters, namely resistive index (RI) and pulsatility index (PI), of the preserved kidney in living donors.

PATIENTS AND METHODS

Our study included 58 donors, divided into 2 groups according to age; the elderly donor group was comprised of those 65 years old or older. We measured length, width, and short diameter of the preserved kidney using Doppler ultrasonography, and calculated kidney volume.

RESULTS

The elderly group was comprised of 13 patients. In this group, the median preserved kidney volume was 145.0 cm(3) (101.8-193.5) before nephrectomy, and 127.6 cm(3) (99.0-183.4) and 145.5 cm(3) (141.3-148.6) at 1 and 12 months after nephrectomy, respectively. We did not observe significant compensatory hypertrophy in the preserved kidneys of elderly donors postoperatively. Both the mean PI and RI values of elderly donors increased progressively after nephrectomy. No compensatory hypertrophy occurred in the preserved kidneys of elderly donors, although the PI and RI did increase in these donors.

CONCLUSION

Our results indicate that nephrectomy caused nephrosclerosis in the preserved kidneys of elderly donors and that prevention of hypertension may be important after nephrectomy in elderly donors.

A requirement of serotonergic p38α mitogen-activated protein kinase for peripheral immune system activation of CNS serotonin uptake and serotonin-linked behaviors

Alterations in central serotonin (5-hydroxytryptamine, 5-HT) neurotransmission and peripheral immune activation have been linked to multiple neuropsychiatric disorders, including depression, schizophrenia and autism. The antidepressant-sensitive 5-HT transporter (SERT, SLC6A4), a critical determinant of synaptic 5-HT inactivation, can be regulated by pro-inflammatory cytokine signaling. Systemic innate immune system activation via intraperitoneal lipopolysaccharide (LPS) injection rapidly elevates brain SERT activity and 5-HT clearance. Moreover, the pro-inflammatory cytokine interleukin (IL)-1β rapidly stimulates SERT activity in raphe nerve terminal preparations ex vivo, effects that are attenuated by pharmacological p38 MAPK inhibition. To establish a role of serotonergic p38α MAPK signaling in LPS/IL-1β-induced SERT regulation and attendant behavioral responses, we pursued studies in mice that afford conditional elimination of p38α MAPK in 5-HT neurons (p38α(5HT-)). We found p38α(5HT-) and control (p38α(5HT+)) littermates to be indistinguishable in viability and growth and to express equivalent levels of SERT protein and synaptosomal 5-HT transport activity. Consistent with pharmacological studies, however, IL-1β fails to increase SERT activity in midbrain synaptosomes prepared from p38α(5HT-) animals. Moreover, although LPS elevated plasma corticosterone and central/peripheral pro-inflammatory cytokines in p38α(5HT-) animals, elevations in midbrain SERT activity were absent nor were changes in depressive and anxiety-like behaviors observed. Our studies support an obligate role of p38α MAPK signaling in 5-HT neurons for the translation of immune activation to SERT regulation and 5-HT-modulated behaviors.

Synergistic Effects of Calcineurin Inhibitors and Steroids on Steroid Sensitivity of Peripheral Blood Mononuclear Cells

The steroid receptor (SR) complex contains FKBP51 and FKBP52, which bind to tacrolimus (TAC) and cyclophilin 40, which, in turn, bind to cyclosporine (CYA); these influence the intranuclear mobility of steroid-SR complexes. Pharmacodynamic interactions are thought to exist between steroids and calcineurin inhibitors (CNIs) on the SR complex. We examined the effect of CNIs on steroid sensitivity. Methylprednisolone (MPSL) sensitivity was estimated as the concentration inhibiting mitosis in 50% (IC50) of peripheral blood mononuclear cells and as the area under the MPSL concentration-proliferation suppressive rate curves (CPS-AUC) in 30 healthy subjects. MPSL sensitivity was compared between the additive group (AG) as the MPSL sensitivity that was a result of addition of the proliferation suppressive rate of CNIs to that of MPSL and the mixed culture group (MCG) as MPSL sensitivity of mixed culture with both MPSL and CNIs in identical patients. IC50 values of MPSL and cortisol sensitivity were examined before and 2 months after CNI administration in 23 renal transplant recipients. IC50 and CPS-AUC values of MPSL were lower in the MCG than in the AG with administration of TAC and CYA. The CPS-AUC ratio of MCG and AG was lower in the TAC group. IC50 values of MPSL and cortisol tended to be lower after administration of TAC and CYA, and a significant difference was observed in the IC50 of cortisol after TAC administration. Steroid sensitivity increased with both TAC and CYA. Furthermore, TAC had a greater effect on increasing sensitivity. Thus, concomitant administration of CNIs and steroids can increase steroid sensitivity.

Clinical significance of peripheral blood lymphocyte sensitivity to glucocorticoids for the differentiation of high-risk patients with decreased allograft function after glucocorticoid withdrawal in renal transplantation

PURPOSE

A reliable biomarker to differentiate high-risk recipients who will experience a decrease in allograft function after glucocorticoid withdrawal has not been established in renal transplantation. We examined the clinical significance of peripheral blood lymphocyte sensitivity to glucocorticoids in vitro for the differentiation of the high-risk patients after glucocorticoid reduction/withdrawal in renal transplant recipients.

METHODS

The study included 44 renal transplant recipients with stable allograft function. Peripheral lymphocyte responses to suppressive effects of cortisol, methylprednisolone, cyclosporine, and tacrolimus in mitogen assay procedures in vitro were examined. Clinical outcome after glucocorticoid reduction/withdrawal was retrospectively compared between recipients with lymphocytes normally sensitive to the drugs and those with hyposensitivity. The receiver-operating characteristic (ROC) curve analysis was undertaken for setting the cutoff IC50 values of the drugs against the T cell mitogen-induced lymphocyte proliferation to differentiate the high-risk recipients with decreased allograft function after glucocorticoid withdrawal.

FINDINGS

The median (range) IC50 value for cortisol in the recipients who showed decreased renal function due to glucocorticoid withdrawal was 10,000 (570.9-72,279.3) ng/mL (n = 9), which was significantly higher than the value of 351.6 (2.0-10,000) ng/mL in the recipients who had not experienced glucocorticoid withdrawal symptoms (n = 35) (P < 0.001). Similarly, the median (range) IC50 value for methylprednisolone in the recipients who showed decreased renal function after glucocorticoid withdrawal was 69.1 (21.5-1442.7) ng/mL (n = 9), which was significantly higher than the value of 13.8 (0.7-1000) ng/mL in the recipients who had not experienced glucocorticoid withdrawal symptoms (n = 30) (P < 0.003). In contrast, there was no significant difference in the median IC50 values of cyclosporine and tacrolimus between the 2 recipient subgroups. The ROC curve analyses for the IC50 values of the immunosuppressive drugs estimated the cutoff value of cortisol and methylprednisolone to be 3580.0 and 21.5 ng/mL, respectively. The ROC AUCs for cortisol and methylprednisolone were 0.83 and 0.84, respectively. According to the cutoff IC50 value, the incidence of decreased allograft function in the low cortisol sensitivity (IC50 >3580.0 ng/mL) subgroup was 7 of 13 patients, which was significantly higher than that of the higher sensitivity subgroup of 2 of 31 (P = 0.0012). A similar case was observed using the cutoff IC50 value of methylprednisolone (P = 0.0012), whereas recipient grouping according to the cutoff IC50 values of cyclosporine and tacrolimus failed to differentiate the high-risk recipients with decreased allograft function after glucocorticoid withdrawal.

IMPLICATIONS

Glucocorticoid pharmacodynamics in lymphocytes of individual patient origin is a reliable biomarker for differentiation of renal transplant recipients who will experience a safe reduction/withdrawal of glucocorticoid.

Time course analysis of mechanical ventilation-induced diaphragm contractile muscle dysfunction in the rat

Controlled mechanical ventilation (CMV) plays a key role in triggering the impaired diaphragm muscle function and the concomitant delayed weaning from the respirator in critically ill intensive care unit (ICU) patients. To date, experimental and clinical studies have primarily focused on early effects on the diaphragm by CMV, or at specific time points. To improve our understanding of the mechanisms underlying the impaired diaphragm muscle function in response to mechanical ventilation, we have performed time-resolved analyses between 6 h and 14 days using an experimental rat ICU model allowing detailed studies of the diaphragm in response to long-term CMV. A rapid and early decline in maximum muscle fibre force and preceding muscle fibre atrophy was observed in the diaphragm in response to CMV, resulting in an 85% reduction in residual diaphragm fibre function after 9-14 days of CMV. A modest loss of contractile proteins was observed and linked to an early activation of the ubiquitin proteasome pathway, myosin:actin ratios were not affected and the transcriptional regulation of myosin isoforms did not show any dramatic changes during the observation period. Furthermore, small angle X-ray diffraction analyses demonstrate that myosin can bind to actin in an ATP-dependent manner even after 9-14 days of exposure to CMV. Thus, quantitative changes in muscle fibre size and contractile proteins are not the dominating factors underlying the dramatic decline in diaphragm muscle function in response to CMV, in contrast to earlier observations in limb muscles. The observed early loss of subsarcolemmal neuronal nitric oxide synthase activity, onset of oxidative stress, intracellular lipid accumulation and post-translational protein modifications strongly argue for significant qualitative changes in contractile proteins causing the severely impaired residual function in diaphragm fibres after long-term mechanical ventilation. For the first time, the present study demonstrates novel changes in the diaphragm structure/function and underlying mechanisms at the gene, protein and cellular levels in response to CMV at a high temporal resolution ranging from 6 h to 14 days.

Correlation between post kidney transplant anemia and kidney graft function

BACKGROUND

Posttransplant anemia (PTA) influences kidney graft function and prognosis; however, there is no consensus regarding target hemoglobin (Hb) levels.

METHODS

We examined several cases of PTA to identify any correlation between Hb levels and graft function. We evaluated 84 kidney transplant recipients (50 men and 34 women; mean age, 46.7 years) who were treated at our department between February 2004 and March 2012 and were available for a 2-year post-transplant follow-up.

RESULTS

Hb levels and serum creatinine levels before transplantation and at 1, 3, 6, 12, and 24 months after transplantation were compared. We examined the correlation between the degree of anemia and renal function among the patients. Data were analyzed using Spearman's rank correlation coefficient and Friedman tests. The mean pretransplantation Hb level was 10.4 g/dL, whereas Hb levels at 6, 12, and 24 months after transplantation were significantly increased to 11.6, 12.2, and 12.4 g/dL, respectively, suggesting an improvement in anemia after the transplantation. Correlation analysis between anemia and kidney graft dysfunction revealed significant correlations at 1, 3, 12, and 24 months after transplantation. Subjects were stratified for correlation analysis according to Hb level at 24 months after transplantation: <10, 10-10.9, 11.0-11.9, 12.0-12.9, and ≥ 13.0 g/dL. A significant improvement in kidney graft function was noted in patients with an Hb level ≥ 11 g/dL at 2 years after transplantation. Anemia improved significantly by 3 months after transplantation.

CONCLUSIONS

A significant correlation between PTA and kidney graft function was apparent, and the prognosis for kidney graft function was poor in patients with Hb levels ≤ 11 g/dL.

Relationship among collagen amount, distribution and architecture in the M. longissimus thoracis and M. pectoralis profundus from pigs

The relative distribution of types I and III collagens and collagen fibre architecture in the perimysium and endomysium were compared to the longissimus thoracis (LT) and pectoralis profundus (PP) muscles in pigs. The LT muscle was composed of type I myofibres 16.8%, IIA 12.9% and IIB 70.2%, and the PP muscle was 25.4, 23.1 and 51.5%, respectively. The total collagen amount differed significantly between the LT (2.66 mg/g) and PP (4.13 mg/g) muscle (P<0.001). On image analysis of the immunohistochemical preparations for types I and III collagens, the percentage area of the perimysium to the total collagen area showed significant differences between the muscles, where perimysial type I collagen occupied 25.4% of the total area in the LT muscle and 45.7% in the PP and perimysial type III 37.6 and 54.5%, respectively (P<0.001). In scanning electron microscopic photographs of the macerated preparation, very thick collagen layers composed of several fibre bands were observed in the perimysia of the PP muscle and appeared differently from the thinner perimysia with a few bands in the LT. Similar architecture of endomysial collagen fibres were observed around every myofibre type in the PP muscle and also in the LT. The fine surface cover of reticular collagen fibres around an adipocyte was shown as a global cast. These results suggested that the total collagen amount of the PP muscle was related mainly to the well developed perimysia composed of several collagen bands, indicating tougher meat compared with the LT muscle.

Long-term recurrence-free survival after liver transplantation from an ABO-incompatible living donor for treatment of hepatocellular carcinoma exceeding Milano criteria in a patient with hepatitis B virus cirrhosis: a case report

The early results of liver transplantations (OLT) in patients with advanced hepatocellular carcinoma (HCC) were poor because of frequent tumor recurrence. However, OLT has significant, theoretical advantage that it removes both the tumor and the organ that is at a risk of malignancy. The Japanese law on organ transplantation limited the availability of cadaveric liver donors until its revision on July 17, 2011. ABO-incompatible OLT was formerly contraindicated because performed anti-A/B antibodies on recipient endothelial cells raised the risk of antibody-mediated humoral graft rejection. We have herein described four successful cases of steroid withdrawal among adult patients who underwent living donor OLT from ABO-incompatible donors. In addition, we transplanted a liver from a living donor into an ABO-incompatible recipient on August 9, 2004. The 55-year-old man with HCC due to hepatitis B virus (HBV) a cirrhosis had a Child-Pugh score of C, and Model for End-stage Liver Disease score of 22. Two tumors greater than 5 cm, exceeded the Milan criteria. His des-gamma-carboxy prothrombin level was 6 mAu/mL, and alpha-fetoprotein, 18.78 ng/mL. Antirejection therapy included multiple perioperative plasmaphereses and splenectomy; with an immunosuppressive regimen consisting of tacrolimus, methylprednisolone, and mycophenolate mofetil. The maintenance dose of immunosuppression did not differ from that of ABO-identical cases. After transplantation, we used intrahepatic arterial infusion therapy with prostaglandin E1 (PG E1). The patient had complications of portal vein thrombosis, hepatic artery thrombosis, and acute myocardial infarction, which were treated by interventional radiology in the posttransplantation period. We controlled the HBsAb titer by administering hepatitis B immunoglobulin and lamivudine (200 IU/L doses) for 1 year after OLT and 100 IU/L doses thereafter. As a result, the patient achieved long-term, disease-free graft survival without steroids. He currently has good liver function and leads a normal lifestyle. Our results suggested the feasibility of controlling antibody-mediated humoral rejection and other complications in living donor liver transplantations into ABO-incompatible adults via intrahepatic arterial PG E1 infusion splenectomy, and plasmapheresis with regular immunosuppression. Withdrawal of steroids, HBV vaccination, and lamivudine, an nucleoside analog reverse transcriptase inhibitor, have achieved long-term (7 years) survival without recurrent HBV infection or tumor.

Steroid withdrawal based on lymphocyte sensitivity to endogenous steroid in renal transplant recipients

Though steroid withdrawal is done in many renal transplant recipients, some patients must restart steroids. Little report has investigated steroid withdrawal under pharmacodynamic monitoring. We assessed lymphocyte sensitivity to endogenous cortisol as a biomarker for determining the safety of steroid withdrawal in renal transplant patients, as we hypothesized that patients hyposensitive to cortisol could not be sufficiently immunosuppressed by their intrinsic cortisol as a substitute for the reduced or withdrawn steroid. Lymphocyte sensitivity to cortisol was examined in 30 long stable renal transplant recipients. Lymphocyte sensitivity to cortisol and its relationship with the clinical outcome after steroid reduction and withdrawal was investigated. The lymphocyte sensitivities to cortisol were estimated as IC(50) of lymphocyte blastogenesis. The lymphocyte proliferation rate for concentration of serum cortisol compared between incident and non-incident groups. Serum creatinine levels (S-Cr) increased in a significantly higher number of patients hyposensitive to cortisol (IC(50)≧10000 ng/ml) than in normally sensitive patients (IC(50)<10000 ng/ml). The incidences of steroid withdrawal syndrome and necessity for increasing steroid dose or restarting steroid administration were also higher in the patients hyposensitive to cortisol. The patients in whom the lymphocyte proliferation rate was less than 60% did not show increase in S-Cr, experience steroid withdrawal symptoms, or require an increase in the steroid dose or restart of steroid administration. The patients who have the normal IC(50) values of cortisol, can withdraw steroid more safely. The lymphocyte sensitivity to cortisol may be a useful biomarker for selecting patients who can sustain steroid withdrawal.

Higher Sensitivity of Peripheral Blood Lymphocytes to Endogenous Glucocorticoid in Renal Transplant Recipients Treated With Tacrolimus, as Compared to Those Treated With Cyclosporine

Lymphocyte sensitivity to endogenous glucocorticoid cortisol could be a biological marker for safe reduction and withdrawal of steroids in renal transplant recipients. We compared peripheral lymphocyte sensitivity with cortisol between transplant recipients treated with tacrolimus (Tac) and those treated with cyclosporine. The suppressive efficacies of cortisol against T-cell mitogen-stimulated proliferation of peripheral lymphocytes were investigated in 44 renal transplant patients, who either had reduced or been withdrawn from steroid treatment. Twenty of the 44 patients were treated with Tac, and the other 24 patients were treated with cyclosporine A (CyA). The lymphocyte sensitivity to cortisol was compared between these two patient groups. The cortisol IC50 values in the Tac and CyA groups were 0.09 ± 0.12 and 14.2 ± 12.7 ng/ml, respectively. Lymphocyte sensitivity to cortisol in the Tac-treated group was significantly higher than that in the CyA-treated group (p = 0.0283). On the other hand, incidences of steroid withdrawal syndrome and increases in serum creatinine concentration were not significantly different between the Tac and CyA groups. Lymphocyte sensitivity to cortisol was higher in the Tac-treated patients than that in the CyA-treated ones. Since the cortisol sensitivity of peripheral lymphocytes is suggested to be a predictive marker for safe steroid withdrawal, Tac administration shows promise in aiding successful withdrawal of steroid treatment in long-term renal transplant recipients.

Characterization of intestinal absorption of quinidine, a P-glycoprotein substrate, given as a powder in rats

The characteristics of intestinal absorption of quinidine, a P-glycoprotein (P-gp) substrate in biopharmaceutics classification system (BCS) Class I, after oral administration as a powder in No. 9 HPMC capsule (diameter 2.6 mm; length 8.4 mm, volume 25 microl) was examined in rats from the following viewpoints: (i) main absorption site of quinidine, (ii) effect of dosage amounts (or luminal concentrations) of quinidine (10 mg vs 0.1 mg/kg), (iii) contribution of P-gp in quinidine absorption (0.1 mg/kg), and (iv) effect of gastric pH on quinidine absorption. Quinidine administered orally at a dose of 10 mg/kg was discharged from the stomach steadily with time and disappeared rapidly from the proximal intestine, where P-gp expression was low. In contrast, quinidine administered at a dose of 0.1 mg/kg remained longer in the gastrointestinal lumen than that administered at a dose of 10 mg/kg. The pretreatment with cyclosporine A, a P-gp inhibitor, greatly increased the intestinal absorption of quinidine given at a dose of 0.1 mg/kg. The gastric pH in untreated control rats was pH 3.6, and the treatment with ranitidine (10mg/kg, ip), a H2 blocker, increased to pH 6.4. The recovered amounts of quinidine 30 min after administration were 21.1% of dose in control rats and 94.7% in ranitidine-treated rats. The value of plasma AUC(0-6h) of quinidine in ranitidine-treated rats was about 40% that in untreated control rats. In conclusion, quinidine was rapidly and efficiently absorbed at the proximal intestine under ordinary circumstances. However, the oral bioavailability was modulated by various factors including the dose (or luminal concentration at the absorption site), presence of P-gp inhibitors, and gastrointestinal pH.