Effect of thromboxane synthetase inhibition and angiotensin converting enzyme inhibition on acute cyclosporin A nephrotoxicity

One component of cyclosporin A (CsA) nephrotoxicity is thromboxane (Tx) A2 induced renal vasoconstriction. This study was designed to investigate whether coadministration of angiotensin converting enzyme inhibitors (ACEI) and thromboxane synthetase inhibition (TSI) could act synergistically to improve the glomerular filtration rate in CsA treated animals. CsA administration (50 mg/kg/day p.o.) to Sprague-Dawley rats for 14 days caused a significant decline in creatinine clearance (CCR), an increase in N-acetyl-beta-D-glucosaminidase (NAG) enzymuria and renal tubulointerstitial damage. These changes were associated with a ten-fold increase in urinary TxB2 excretion (from pretreatment values of 17.2 +/- 6.0 ng/day to 174.9 +/- 65.4 ng/day on day 14). Treatment with TSI normalized TxB2 excretion; this was associated with partial protection against CsA induced changes in CCR and NAG enzymuria and the complete prevention of acute proximal tubular vacuolation. However, the coadministration of both TSI and ACEI removed the protective effects exerted by TSI alone and resulted in elevated urinary TxB2 levels similar to those observed in other CsA treated groups. Treatment with ACEI alone did not affect CsA nephrotoxicity. We suggest that elevated TxB2 synthesis is in part responsible for some aspects of renal functional and morphological damage, but that CsA nephrotoxicity is multifactorial and may result from direct cellular toxicity in addition to vascular changes.     

Optimization of sampling time for cyclosporine monitoring in transplant patients.

Cyclosporine (CsA) dosing is based on CsA plasma or blood concentrations measured 12 to 24 hours after drug administration (trough levels). This study evaluated the relationship between the timing of CsA concentrations and subsequent pharmacokinetic parameters to predict an optimal sampling period. Plasma samples were obtained from 22 patients before their morning dose of CsA and at 2, 4, 6, 8, 10, and 12 hours after the dose on the 7th and on the 21st day after heart transplantation. The plasma samples were assayed by both HPLC and FPIA. The Cmax for CsA was achieved over a period ranging from 2 to 6 hours (mean/median = 4.7/4.0) during the day 7 and the day 21 studies. The mean (+/- SD) half-life was 3.2 (1.0) hours on day 7 and 2.9 (1.1) hours on day 21, (P > 0.05); the mean apparent oral clearance was 276 (117) L/hr on the day 7 and 269 (209) L/hr on day 21, (P > 0.05). When CsA plasma concentration by either FPIA and HPLC was monitored, the drug concentration best correlated with AUC was found to correspond to the plasma samples taken 4 to 8 hours after drug administration. The authors conclude that through blood sampling for therapeutic drug monitoring of CsA is not optimal, and that further studies are necessary to correlate concentration monitoring during the dosing interval with pharmacologic and toxicologic parameters.     

Circadian variations in the pharmacokinetics, tissue distribution and urinary excretion of nifedipine after a single oral administration to rats

Circadian variations in the pharmacokinetics, tissue distribution and urinary excretion of nifedipine were examined in fasted rats after administering a single oral dose at three different dosing times (08:00 am, 16:00 pm, 00:00 am). The plasma concentrations, the areas under the plasma concentration-time curve from zero to 6 h (AUC(0-6 h)) and the peak plasma concentration (C(max)) were significantly higher in the rats dosed at 08:00 am (immediately inactive), and was lower at 16:00 pm (most inactive) and 00:00 am (most active). The time to reach the C(max) (T(max)) was the shortest in the rats dosed at 08:00 am. It was very interesting to observe the double peak phenomena in the plasma concentration profiles, showing a larger peak followed by a smaller peak. There was a dosing time dependency on the tissue distribution 30 min after administration, showing a similar tendency to the pharmacokinetic behavior. However, there was no distinct dosing time dependency observed at 2 h after administration due to the extensive disposition. The cumulative urine excretion of nifedipine in the rats dosed at 08:00 am was significantly higher (about two-fold) than in those dosed at 16:00 pm and 00:00 am. The pharmacokinetics of nifedipine in the rats was consistent with that observed in human subjects in terms of the day-night clock time but the biological time was the opposite, as marked by the rest-activity cycles. These results may help to explain the circadian time-dependency of nifedipine pharmacokinetics.     

Assessment of renal dopaminergic system activity during cyclosporine A administration in the rat.

1. Administration of cyclosporine A (CsA; 50 mg kg-1 day-1, s.c.) for 14 days produced an increase in both systolic (SBP) and diastolic (DBP) blood pressure by 60 and 25 mmHg, respectively. The urinary excretion of dopamine, DOPAC and HVA was reduced from day 5-6 of CsA administration onwards (dopamine from 19 to 46%, DOPAC from 16 to 48%; HVA from 18 to 42%). In vehicle-treated rats, the urinary excretion of dopamine and DOPAC increased (from 7 to 60%) from day 5 onwards; by contrast, the urinary excretion of HVA was reduced (from 27 to 60%) during the second week. 2. No significant difference was observed between the Vmax and Km values of renal aromatic L-amino acid decarboxylase (AAAD) in rats treated with CsA for 7 and 14 days or with vehicle. 3. Km and Vmax of monoamine oxidase types A and B did not differ significantly between rats treated with CsA for 7 and 14 days or with vehicle. 4. Maximal catechol-O-methyltransferase activity (Vmax) in homogenates of renal tissues obtained from rats treated with CsA for 7 or 14 days was significantly higher than that in vehicle-treated rats; Km (22.3 +/- 1.5 microM) values for COMT did not differ between the three groups of rats. 5. The accumulation of newly-formed dopamine and DOPAC in cortical tissues of rats treated with CsA for 14 days was three to four times higher than in controls. The outflow of both dopamine and DOPAC declined progressively with time and reflected the amine and amine metabolite tissue contents. No significant difference was observed between the DOPAC/dopamine ratios in the perifusate of renal tissues obtained from CsA- and vehicle-treated rats. In addition, no significant differences were observed in k values or in the slope of decline of both DA and DOPAC between experiments performed with CsA and vehicle-treated animals. 6. The Vmax for the saturable component of L-3,4-dihydroxyphenylalanine (L-DOPA) uptake in renal tubules from rats treated with CsA was twice that of vehicle-treated animals. Km in CsA- and vehicle-treated rats did not differ. 7. The decrease in the urinary excretion of sodium and an increase in blood pressure during CsA treatment was accompanied by a reduction in daily urinary excretion of dopamine. This appears to result from a reduction in the amount of L-DOPA made available to the kidney and does not involve changes in tubular AAAD, the availability of dopamine to leave the renal cells and dopamine metabolism.(ABSTRACT TRUNCATED AT 400 WORDS)     

环孢素对早期糖尿病肾病大鼠肾脏的保护作用

目的研究环孢素(CsA)对实验性1型糖尿病大鼠早期肾脏损害的保护作用。方法将健康雄性Wistar大鼠分成3组,即单肾切除对照组24只,糖尿病(DM)组30只,糖尿病环孢素A治疗组30只,后两组每日注射中效胰岛素(NPH)1～4U,使血糖维持在11.1～22.2mmol/L,在糖尿病成模后每日管饲DM+CsA组大鼠CsA10mg/kg,其余两组管饲等量蒸馏水。分别于饲养2、4、8周后处死各组1/3量大鼠,检测肾重、血糖、内生肌酐清除率、24h尿白蛋白排泄率。结果DM组大鼠随着病程的延长肾重增加,内生肌酐清除率增高,并出现进行性微量白蛋白尿,与各时段对照组比较差异有统计学意义(P<0.05);而DM+CsA组大鼠肾重低于各时段DM组肾重,但差异无统计学意义(P>0.05),内生肌酐清除率8周时明显低于DM组[(4.5±0.7)ml/minvs(7.3±2.9)ml/min,P<0.05],24h尿白蛋白排泄率于2、4、8周时均低于DM组(P<0.05)。结论CsA对1型糖尿病大鼠早期肾脏损害有保护作用,其机制主要是通过抗炎、抗增殖作用产生。     

Dosing time dependency of doxorubicin-induced cardiotoxicity and bone marrow toxicity in rats

Cardiac toxicity caused by doxorubicin (adriamycin) is a serious dose-limiting factor in the clinical situation. However, the influence of doxorubicin dosing time has not been clarified from the viewpoints of cardiotoxic development and its mechanism. In this study, we have investigated the dosing time dependency of doxorubicin-induced cardiotoxicity and bone marrow toxicity after repeated administration of doxorubicin in rats. When doxorubicin (5 mg kg(-1), i.p.) was administered every seven days (total of 30 mg kg(-1)) at 3, 9, 15 or 21 h after the light was turned on (HALO), toxic death was significantly higher in the 9 HALO treated group than the other groups. When doxorubicin was injected every seven days for 28 days at 9 or 21 HALO, we measured the levels of creatine kinase, malondialdehyde (MDA; an index of lipid peroxide), and glutathione peroxidase (GPx) as markers of cardiotoxicity. On days 14 and 28, creatine kinase levels were significantly higher in the 9-HALO group compared with the 21-HALO group (P< 0.01, respectively). On day 14, MDA levels increased significantly in the 9 HALO group compared with the 21 HALO group (P< 0.01). A single dose of doxorubicin was administered at 9-h or 21-h after the light was turned on to investigate the dosing-time-dependent difference of the pharmacokinetics. The area under the plasma time-concentration curve showed a significant increase at 9 HALO compared with 21 HALO (P< 0.05). These results suggested that the dosing-time-dependent difference of cardiotoxicity induced by doxorubicin was closely related to the daily variation of doxorubicin pharmacokinetics. In conclusion, the choice of optimal dosing time based on the chronopharmacokinetics of doxorubicin may decrease the cardiotoxicity and enable the practice of effective and safe chemotherapy of doxorubicin.     

Effects of dosing time and schedule on cisplatin-induced nephrotoxicity in rats

Renal dysfunction induced by a single injection of cisplatin depends on the timing of the dose. However, the effects of repeated administration of cisplatin on time-dependent toxicity have not been evaluated despite the fact that in clinical practice high doses are repeatedly injected at intervals or low doses are administered daily. We studied chrononephrotoxicity in rats after weekly or daily cisplatin injections. Weekly high doses (5 mg kg(-1)) or daily low doses (1.2 mg kg(-1)) of cisplatin were injected at four time points (3, 9, 15 and 21 h after the light was turned on (HALO)) for 3 weeks. Changes in body weight after weekly cisplatin administration were independent of the timing of the doses. In the group that received daily cisplatin, the loss in body weight in the 3 HALO group was smaller than in animals receiving injections at 15 and 21 HALO (P < 0.05 and 0.001, respectively). The blood urea nitrogen and serum creatinine levels in the control rats showed a significant circadian change (peak at 15 HALO and trough at 9 HALO), but these parameters were markedly elevated in both trials and their circadian variations were disturbed. In conclusion, cisplatin-induced nephrotoxicity was the lowest at 3HALO compared with other time points of both dose regimens.     

Alpha-fluoromethylhistidine, an inhibitor of histamine biosynthesis, causes arterial hypertension

In this study we assessed the cardiovascular response to 13 days of irreversible inhibition of the enzyme histidine-decarboxylase (HD) with alpha-fluoromethylhistidine (AFMH). Age-matched untreated rats were used as controls. Tail-cuff mean arterial pressure (MAP) and heart rate (HR) rose progressively in AFMH-treated rats, reaching maximal values during the study period by the 13th day of treatment. There was a reduction in urinary histamine at the day 7 and 13, and of sodium excretion at the day 7 of treatment, while the renal catecholamine excretion was increased at both days of treatment, suggesting an increase of sympathetic activity. At the 13th day of treatment, there was an activation of the renin-angiotensin-aldosterone system. In addition, the cardiovascular responses to footshock stress were determined in rats treated intraperitoneally (i.p.) or intracerebroventricularly (i.v.t.) with a single dose of AFMH. Peripheral sympathetic facilitation was found, as the hemodynamic response to footshock stress was significantly enhanced after i.p. administration, but not after i.v.t. administration of AFMH. Our results suggest that conditions of peripheral histamine deficiency may result in sympathetic facilitation, arterial hypertension and tachycardia in the rat.     

Disease modifying activity of HWA 486 in rat adjuvant-induced arthritis

HWA 486 was investigated for its ability to modify the development of adjuvant-induced polyarthritis in Lewis rats. HWA 486 (20 mg/kg/day p.o.), dosed for 8 or 16 days beginning with the day of adjuvant administration, significantly reduced edema, fibrinogen levels, and erythrocyte sedimentation rates (ESR) 42 days later. When HWA 486 (20 mg/kg/day, p.o.) and cyclosporin A (CsA 15 mg/kg/day, p.o.) were tested in the 8-day treatment regimen, the antiarthritic effects of HWA 486 were more sustained. Both compounds reduced the delayed hypersensitivity (DTH) response on day 9 followed by a rebound to an enhanced DTH response on day 21. The PHA-induced mitogenic response of splenocytes from arthritic rats was suppressed on day 9. Treatment with HWA 486 but not CsA restored the splenocyte response to the level of the negative controls.     

Studies on absorption, distribution and excretion of 14C labeled pivaloyloxymethyl (+)-(6R,7R)- 7-[(Z)-2-(2-amino-4-thiazolyl)-2-methoxyiminoacetamido]- 3-[(5-methyl-2H-tetrazol-2-yl)methyl]-8-oxo-5-thia- 1-azabicyclo[4.2.0]oct-2-ene-2-carboxylate (14C-T-2588) in rats and mice

Absorption, distribution and excretion of T-2588 were studied in rats and mice using (aminothiazole-2-14C) T-2588 and (pivaloyloxymethyl-14C) T-2588. Results are summarized below. The binding rate of 14C-T-2525, an activated form of 14C-T-2588 in vivo, to serum protein was 90 approximately 100% in rats and mice after an oral administration of (aminothiazole-2-14C) T-2588. Blood levels of radioactivity reached to the highest concentration at 1 hour after an oral administration of (aminothiazole-2-14C) T-2588 to rats, and then gradually diminished. After an oral administration of (aminothiazole-2-14C) T-2588 to rats and mice, the highest radioactivity distribution was found in kidney among all the organs except stomach, intestine and bladder. Radioactivity was widely distributed into other organs such as adrenal, lung, liver, heart and pancreas. But little radioactivity was found in the brain. In new born rats, tissue levels of radioactivity were lower and diminished slower than those of adult rats. After an oral administration of (aminothiazole-2-14C) T-2588 to rats and mice, urinary excretion of radioactivity was about 26% and 35% of the dosed radioactivity in rats and mice, respectively, and fecal excretion was about 76% and 63% of the dosed radioactivity in rats and mice, respectively. Urinary and fecal excretion patterns of radioactivity after multiple oral administration of (aminothiazole-2-14C) T-2588 for 7 days to mice were similar to those after a single administration. This result suggests that T-2588 did not accumulate in the body. After an oral administration of (pivaloyloxymethyl-14C) T-2588 to rats and mice, urinary excretion was both about 8% of the dosed radioactivity, and fecal excretion was both about 6%. Then excretion of 14CO2 into respiratory air was about 55% and 66% of the dosed radioactivity in rats and mice, respectively. Biliary excretion was about 6.5% of the dosed radioactivity after an oral administration of (aminothiazole-2-14C) T-2588 to rats. Small amount of radioactivity was secreted to the milk after intravenous administration of (aminothiazole-2-14C) T-2525 to nursing rats. After an administration of (aminothiazole-2-14C) T-2588 to pregnant mice, radioactivity hardly transferred into the fetus.     

Cyclosporin A enhances the pulmonary granuloma response induced by Schistosoma mansoni eggs

The modulating effect of cyclosporin A (CsA) was studied in the immune-based pulmonary granuloma response to Schistosoma mansoni eggs. The extent of the S. mansoni egg-induced inflammation was quantitated biochemically by measuring total units of N-acetyl-beta-D-glucosaminidase (NAG) and total lung DNA. The enzyme NAG was used as a marker for the activity of inflammatory cells such as macrophages and DNA levels were used to quantify the increased cellularity of the lungs. In this model, the inflammatory response is maximal approximately 2 weeks after egg injection. Daily oral administration of CsA at 50 mg/kg during the first 2 weeks of the response dramatically enhanced the levels of pulmonary inflammation. Similar augmentation of the granuloma response was seen when CsA was given from days 0 to 7 but not when dosed from days 8 to 14. The enhancing of CsA was seen in the high-responder strains C57BL/10, B10.BR and CBA and in a lower-responder strain, Balb/c. Both the S. mansoni egg-induced granuloma response and the CsA-induced enhancement were dependent on functional T cells: athymic C57BL/6 nude (nu/nu) mice developed minimal responses to S. mansoni eggs which CsA did not augment, while heterozygous (nu/+) euthymic B6 mice responded to S. mansoni eggs and CsA. It appears in this model system that CsA may inhibit the activity of suppressor inducer or suppressor T cells. Cyclophosphamide, a drug known to reduce suppressor cell function, augmented the egg-induced inflammatory response similar to CsA. The enhancing activities of CsA and cyclophosphamide were not additive, suggesting effects on a common pathway of biologic activity, the generation of suppressor cells. While CsA and cyclophosphamide augmented the inflammatory process, conventional immunosuppressive drug therapies, dexamethasone and BW755c, quantifiably reduced the levels of NAG and DNA. These results demonstrate that CsA, rather than being immunosuppressive, augments this immune-based model of inflammation. In addition, this study shows that pulmonary granulomatous inflammation can be quantified biochemically with assays for both NAG and DNA.     

Studies on the pharmacokinetics of BMY-28100 (II)

Studies were done in rats on placental transfer and excretion into milk of 14C-BMY-28100 upon single oral administration. Studies on absorption, distribution and excretion of 14C-BMY-28100 were also done upon multiple dosing. 1. Fetal tissue concentration of the drug reached a maximum at 6 hours after dosing on day 18 of gestation. The highest concentration observed was only 0.56 microgram equiv./g in fetal kidney; The transfer of radioactivity into the fetus was low. Similar results were obtained from whole body autoradiograms performed in rats on day 12 and day 18 of gestation. 2. Concentrations of radioactivity in milk reached a maximum of 0.60 microgram equiv./ml at 1 hour after administration, and gradually decreased thereafter. The maximum concentration in milk was 10% of the plasma concentration measured at the same time. 3. In the multiple oral administration study, 24 hours blood levels of radioactivity rose progressively with each dose, and reached a level 3.8 times higher than that observed with single dosing by the final (21st) administration. Tissue concentrations were relatively high in aorta, kidney and large intestine as were found upon single administration. However, the ratios of these levels between multiple and single dosing were lower than those observed in blood; 1.7, 3.6 and 2.9 for aorta, kidney and large intestine, respectively. Urinary and fecal excretion were constant after the 2nd administration.     

The effect of sodium intake on the urinary histamine in adrenalectomized rats

The daily excretion (μg/day) of free histamine has been measured in bilaterally adrenalectomized or sham-operated female rats. In rats developing adrenal insufficiency when kept on a “sodium free” diet, the output of free histamine in the urine fell progressively. The volume of urine was unchanged. In rats with adrenal insufficiency the oral administration of 0.9% saline caused an immediate rise in the urinary excretion of histamine. The rise was sustained for several days. Adrenalectomized rats consuming 43 mg/day of sodium chloride or less developed adrenal insufficiency and the daily output of urinary histamine fell progressively. A sodium chloride intake of 90 mg/day prevented this fall. Adrenalectomized rats kept on 0.9% saline showed no significant changes during the first 7 days after adrenalectomy. From the 8th day onwards the daily output of histamine in the urine rose progressively. After sham operation the daily output of histamine in the urine was not affected by the intake of sodium chloride. Adrenalectomized rats eat less food; a similar restriction of food intake in sham-operated rats decreased the urinary excretion of histamine. The decrease was, however, not as pronounced as in adrenalectomized rats developing adrenal insufficiency. Other sodium salts, but not glucose, had the same effect as 0.9% saline on the urinary excretion of histamine in adrenalectomized rats.     

Different inhibitory actions of cyclosporine A and cyclosporine A-acetate on lipopolysaccharide-, interleukin 1-, 1,25 dihydroxyvitamin D3- and parathyroid hormone-stimulated calcium and lysosomal enzyme release from mouse calvaria in vitro.

The effects of cyclosporine A (CsA) and one of its immunologically inactive structural analogues, cyclosporine A acetate (CsA-A) on lipopolysaccharide (LPS)-, interleukin-1 (IL-1)-, 1,25 dihydroxyvitamin D3 (1,25 D3)- and parathyroid hormone (PTH)-stimulated bone resorption were tested in mouse calvaria cultures. The release of calcium and a lysosomal enzyme, N-acetylglycosaminidase (NAG) was determined after 3 days of culture. All bone resorbing agents potently stimulated calcium and NAG release. At therapeutic concentration levels of 0.1 and 1.0 micrograms/ml, the immunologically active CsA was significantly more potent than the inactive CsA-A against LPS- and 1,25 D3-induced calcium and NAG release. The inhibition by both cyclosporines of IL-1 and PTH stimulated calcium release was not significantly different. CsA was however more potent than CsA-A against IL-1 stimulated NAG release. PTH-stimulated NAG release was not inhibited by CsA or CsA-A. These findings suggest that both cyclosporines interfere with more than one mechanism of activation of bone resorption. The specific effect of CsA against LPS and 1,25 D3 may be related to its known inhibition of immune cell derived cytokine expression.     

RENAL REGULATION OF PHOSPHATE EXCRETION IN ENDOTOXAEMIC RATS

1. Maintenance of phosphate homeostasis is essential for energy producing and oxygen delivery systems, particularly, when the energy requirements are increased in certain conditions, such as septicaemia. We investigated the phosphaturic response to parathyroid hormone (PTH) in endotoxin (ETx)-treated rats in order to clarify the renal regulation of phosphate excretion during endotoxaemia. 2. Wistar rats that had undergone thyroparathyroidectomy were challenged with either Escherichia coli ETx (n= 8) or saline vehicle (n = 9). Thirty-minute renal clearance tests were done before and after PTH infusion. Rats infused with saline instead of PTH served as time controls for the ETx- (n= 7) and saline-treated (n = 8) rats. 3. In time control rats, ETx administration enhanced phosphate excretion progressively and this was associated with an obvious increase in the level of kidney adenosine 3′,5′-cyclic mono-phosphate (P < 0.005) compared with levels following saline vehicle administration. However, this phosphaturia in late-phase endotoxaemia was not observed in rats infused with PTH; ETx, but not saline vehicle, blunted the PTH-mediated increase in phosphate excretion (P < 0.005). Increased urinary noradrenaline, and constant dopamine excretion were observed in endo-toxaemic rats. Endotoxin administration produced marked metabolic acidosis and hypocapnia in comparison with the administration of the saline vehicle. 4. To test whether renal tubular sensitivity to parathyroid hormone related-protein (PTHrP) was enhanced during endotoxaemia, phosphaturic response to PTHrP in ETx- (n = 7) and saline-treated rats (n= 7) was examined. Parathyroid hormone related-protein infusion produced phosphaturia in both groups. However, the severity of the phosphaturia after PTHrP infusion was less in ETx- than in saline-treated rats. 5. In summary, although ETx administration causes a progressive increase in phosphate excretion in the absence of PTH, this is overcome by the antiphosphaturic effect of ETx, attenuating PTH-mediated phosphaturia after PTH infusion.     

Dosing time-dependent variation of bone resorption by cyclosporin A in rats' femurs

The dosing time-dependent difference of bone resorption by cyclosporin A was determined in normal rats. Rats were kept in rooms with a 12-h light/dark cycle. Cyclosporin A (3 mg/kg, once a day) or vehicle was given at either 2 h after light on (2 HALO) or 8 HALO, 14 HALO, 20 HALO for 24 weeks. Serum and 4-h urine samples were obtained before and at 12 and 24 weeks after the treatment. Body weight, creatinine clearance, serum parathyroid hormone, the trough level of cyclosporin A in whole blood and urinary excretion of Ca and P were not changed by the drug at every any dosing time. Serum Ca and P concentrations by the vehicle treatment differed with the dosing time. Furthermore, increases of these two parameters by the drug varied with dosing time; most prominently at the 2 HALO dosing, and were not seen at the 8 and 14 HALO dosings. Degree of bone resorption of the femur determined by dual-energy X-ray absorption, also varied with dosing time, most prominently at 2 HALO and less prominently at 14 HALO. Increase of urine deoxypyridinoline excretion, a marker of osteoclast activity, by the drug was highest at 2 HALO and lowest at 14 HALO, however parathyroid hormone and osteocalcin concentrations after cyclosporin A treatment did not vary with dosing time. Reduction of urinary nitric oxide (NO) was most prominent at 2 HALO and negligible at 14 HALO. We concluded that cyclosporin A-induced bone resorption and serum Ca and P increases were varied with dosing time. Sensitivity of osteoclasts by the drug was the major mechanisms of the phenomenon, while differences in pharmacokinetics, the parathyroid gland, osteoblasts and renal handling of Ca and P did not contribute to the phenomenon.     

Renal toxicity of propyleneimine: assessment by non-invasive techniques in the rat

The nephrotoxicity of three different dose levels of propyleneimine (10, 20 and 30 microliter/kg body wt) administered intraperitoneally to rats was studied and 20 microliters/kg body weight was found to be the most appropriate sublethal dose. Injection of propyleneimine (10 microliters/kg body wt) produced a small rise in N-acetyl-beta-D-glucosaminidase (NAG) activity, minor histological damage but no change in urine volume. Six rats were injected with 20 microliters/kg body weight, and urine was collected over the following 16 days. An immediate increase in urine volume, osmolality together with a concomitant decrease in specific gravity, was accompanied by a small increase in creatinine excretion and a more marked increase in the sodium and potassium content of urine after the administration of the nephrotoxin. NAG activity increased immediately and peaked on day 3, the activity remained elevated until day 12 when it fell to near normal levels. The activity of both beta-D-galactosidase and beta-D-glucosidase increased 9 days after administration of the nephrotoxin. In contrast, no consistent change was found in the excretion of the brush border marker enzymes, leucine aminopeptidase (LAP), alanine aminopeptidase (AAP) or alkaline phosphatase (ALP). Proteinuria increased sharply the day after injection and remained abnormal. Increased urinary albumin excretion and the predominance of low molecular weight proteins was demonstrated by sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis. Evidence is presented that propyleneimine exerts its early toxic effect on the renal papilla.     

Ototoxicity of toluene in rats

Toluene is a major industrial solvent and substance of abuse which is ototoxic in rats as shown by both behavioral testing and measurement of brainstem auditory evoked response (BAER) thresholds. The objective of this investigation was to examine the morphological (hair cell loss) and functional (BAER threshold elevations) changes resulting from toluene administration. In the preliminary experiment, 5 male Sprague-Dawley rats were dosed by gavage to 0.5 ml toluene/kg body weight/day in corn oil for 21 days then consecutively to 1.0 ml toluene/kg/day for 21 days. In the main experiment, eight male Sprague-Dawley rats were dosed by gavage for eight weeks with 1.0 ml toluene/kg body weight/day in corn oil. Five and six control rats, respectively, received corn oil only. BAER thresholds were recorded from four toluene-treated and four control rats prior to dosing (main experiment) and from all rats after dosing (both experiments). Loss of outer hair cells occurred in all toluene-treated rats in the middle and basal turns of the organ of Corti, with the greatest loss in the third row and progressively less in the second and first rows. This loss was more severe in toluene-treated rats that demonstrated elevated BAER thresholds in midfrequency regions, typically 2–8 kHz. These experiments demonstrate that auditory changes are associated with cochlear hair cell loss in toluene-treated rats. These ototoxic effects of toluene contrast with those of other known ototoxicants, e.g., aminoglycoside antibiotics, in terms of the position of hair cell lesion in the organ of Corti and in the pattern of hair cell loss.     

Chronopharmacology of angiotensin II-receptor blockers in stroke-prone spontaneously hypertensive rats

Protective effect of valsartan (Val), an angiotensin II (AII)-receptor blocker (ARB), against organ damage is reported to depend on the dosing time in hypertensive patients. Dosing-time-dependent effect of Val on survival of stroke-prone spontaneously hypertensive rats (SHRSP) under a 12-h lighting cycle was examined. Val (4 mg/kg per day) and olmesartan medoxomil (OM) (1 mg/kg per day), another ARB with a slower dissociation from the AII receptor, were given once daily at 2, 8, 14, or 20 HALO (hours after lights on). Dosing-time-dependent differences in plasma drug concentrations and effect on blood pressure (BP) were also evaluated. Survival of SHRSP showed a dosing-time-dependent change during Val therapy, with a peak at 2 HALO and a trough at 14 HALO. OM equally prolonged survival in all groups. The BP-lowering effect persisted for more than 24 h after dosing of Val at 2 HALO and of OM at 2 and 14 HALO, but disappeared at 5.5-h after Val dosing at 14 HALO. Plasma concentrations of Val and OM were higher after dosing at 2 HALO than at 14 HALO. These results suggest that the chronopharmacological phenomenon of Val was partly due to the dosing-time-dependent difference in plasma concentration and subsequent duration of the antihypertensive effect. Slower dissociation of OM from AII receptors might have blunted a potential dosing-time-dependent event.     

Green tea extract attenuates cyclosporine A-induced oxidative stress in rats.

Cyclosporine A (CsA) nephrotoxicity underweighs the therapeutic benefits of such a powerful immunosuppressant. Whether oxidative stress plays a role in such toxicity is not well delineated. We investigated the potential of green tea extract (GTE) to attenuate CsA-induced renal dysfunction in rats. Three main groups of Sprague-Dawley rats were used: CsA, GTE, and GTE plus CsA-receiving animals. Corresponding control groups were also used. CsA was administered in a dose of 20mg kg(-1) day(-1), i.p., for 21 days. In the GTE/CsA groups, the rats received different concentrations of GTE (0.5, 1.0 and 1.5%), as their sole source of drinking water, 4 days before and 21 days concurrently with CsA. The GTE group was treated with 1.5% concentration of GTE only for 25 days. A concomitant administration of GTE, to CsA receiving rats, markedly prevented the generation of thiobarbituric acid-reacting substances (TBARS) and significantly attenuated CsA-induced renal dysfunction as assessed by estimating serum creatinine, blood urea nitrogen, uric acid and urinary excretion of glucose. A considerable improvement in terms of reduced glutathione content and activity of antioxidant enzymes in the kidney homogenate of the GTE/CsA-receiving rats was observed. The activity of lysosomal enzymes, N-acetyl-beta-glucosaminidase, beta-glucuronidase and acid phosphatase was significantly inhibited following GTE co-administration. Our data prove the role of oxidative stress in the pathogenesis of CsA-induced kidney dysfunction. Supplementation of GTE could be useful in reducing CsA nephrotoxicity in rats. However, clinical studies are warranted to investigate such an effect in human subjects.