Altered Pharmacokinetics and Dynamics of Apomorphine in the Malnourished Rat: Modeling of the Composed Relationship Between Concentration and Heart-Rate Response

The impact of malnutrition on the pharmacokinetics and pharmacodynamics (change in heart rate) of apomorphine was studied in the rat. One group of rats received a low-protein diet (0.5%) ad libitum to produce prekwashiorkor. The control group received commercial food pellets. In the first experiment, the two groups received a 2 mg/kg iv bolus dose of apomorphine to determine any differences in the basic pharmacokinetic parameters. The pharmacodynamic characteristics in each group were studied at different steady-state plasma levels, achieved by iv infusions with continuous measurements of the heart rate. There was an almost twofold decrease in the plasma clearance in the malnourished rats compared with controls. A pronounced change in the pharmacodynamic response was also observed in the malnourished group. In the control group, apomorphine produced bradycardia at low concentrations and tachycardia at high concentrations, while only bradycardia was registered in the malnourished group, with maximum effects at steady-state plasma concentrations of 50 ng/ml and a return to baseline at higher concentrations. The effects in control and malnourished rats were fitted simultaneously to the sum of two Hill equations with a nonlinear regression program, and the fits were compared by means of an F test. The maximum pure tachycardia obtainable differed significantly in the prekwashiorkor group compared to the control group. These results suggest a selective down regulation/desensitization only of the receptors responsible for the tachycardia produced by apomorphine during malnutrition.     

The Pharmacokinetics and Electroencephalogram Response of Remifentanil Alone and in Combination with Esmolol in the Rat

Purpose. The goal of this study was to determine if the co-administration of esmolol (ES), a short acting cardioselective -blocker, significantly alters the pharmacokinetics and/or pharmacodynamics of remifentanil (REMI), an ultra short-acting opioid, in the rat. Methods. Sprague-Dawley rats (N = 8, Wt. = 325 ± 15g) were surgically implanted with stainless steel cerebrocortical EEG electrodes three days before the study. Each rat was dosed with REMI (15 g/ kg/min), and REMI & ES (15 g/kg/min and 600 g/kg/min) for 21 minutes in a random crossover design. Six serial blood samples were collected over 25 minutes into test-tubes containing 0.5ml acetonitrile. Blood samples were extracted with methylene chloride and analyzed by a validated GC-MS assay. EEG was captured and subjected to power spectral analysis (0.1–50 Hz) for spectral edge (97%). Results. No significant differences (p < 0.05) were found in clearance (REMI = 287 + 73 ml/min/leg vs. REMI & ES = 289 ± 148 ml/ min kg) or Vd (REMI = 286 ± 49 ml/kg vs REMI & ES = 248 + 40 ml/kg). A linked sigmoid E_max PK-PD model was used and the pharmacodynamic parameters were not statistically different. Mean E_max and EC₅₀ after REMI were 18.0 ± 6.0 Hz and 32 ± 12 ng/ml; and after REMI + ES were 19 + 4.8 Hz and 26 + 8.6 ng/ml. Conclusions. At the doses tested, there is no pharmacokinetic or pharmacodynamic interaction between remifentanil and esmolol in the rat.     

大鼠体内槲皮素的血药浓度测定及其药代动力学研究

目的建立测定大鼠血浆中槲皮素浓度的高效液相色谱法,并应用于药代动力学研究。方法10只大鼠(雌雄各半)灌胃给予槲皮素50 mg/kg。采用高效液相色谱法测定槲皮素的血药浓度,以山柰酚为内标,流动相为甲醇-缓冲液(0.1 mol/L NH4AC+0.3 mmol/LEDTA-Na2)-乙酸=(60∶40∶1,V/V),色谱柱为迪马ODS C18柱(250 mm×4.6 mm,5μm),测定波长为370 nm,进样量为20μL,流速为1 mL/min,柱温为35℃。结果槲皮素血药浓度线性范围是0.01～50μg/mL(r=0.999 9),定量下限为0.01μg/mL。低、中、高(0.05,5,25μg/mL)3个质量浓度的回收率为97.2%～103.4%,日内、日间精密度的RSD均小于10%。大鼠灌胃给予槲皮素50 mg/kg后的最大血药浓度为(2.033±0.41)μg/mL,达峰时间为0.5 h,t1/2ke为(4.17±0.64)h,0-∞药时曲线下面积为(6.77±0.80)μg/(h.mL)。结论方法专属性高,准确、灵敏,可为今后槲皮素的药代动力学研究提供方法学依据。     

Modelling acute tolerance to the EEG effect of two benzodiazepines

AIMS: We studied the development of acute tolerance to the EEG effect of midazolam and the new benzodiazepine Ro 48-6791. METHODS: Nine young (24-28 years) and nine elderly (67-81 years) male volunteers received midazolam and Ro 48-6791 computer-controlled, targeting linearly increasing plasma concentrations for 30 min (targeted slopes: 40 and 20 ng ml-1 min-1 for midazolam, 3 and 1.5 ng ml-1 min-1 for Ro 48-6791, for young and elderly, respectively) and a constant concentration for the following 15 min. After recovery, the same infusion scheme was repeated. Plasma concentrations of midazolam, Ro 48-6791 and its metabolite Ro 48-6792 were determined from arterial blood samples. The hypnotic effect was assessed using the median frequency of the EEG power spectrum. RESULTS: The concentration-effect relationship in each infusion cycle could be described by a sigmoid Emax model. The half-maximum concentration EC50 was higher in the second infusion cycle compared with the first one (midazolam, 47% (2.3-91.6%) and 37% (5.3-69.5%); Ro 48-6791, 22% (-2.8% to 44.6%) and 43% (3.4-82.4%) for young and elderly; mean and 95% confidence interval). The complete time course of the EEG median frequency could be described by an interaction between the parent drug in an effect compartment and a hypothetical competitive drug in an additional tolerance compartment. For Ro 48-6791, the use of its metabolite Ro 48-6792 as competitive compound also gave appropriate results. CONCLUSION: Midzolam and Ro 48-6791 showed acute tolerance to the EEG effect which might be caused by competitive interaction with the metabolite.     

UPLC-MS/MS测定大鼠血浆中紫花前胡素的血药浓度及其药动学研究

目的 建立UPLC-MS/MS测定大鼠血浆中紫花前胡素的血药浓度,并用于口服和静脉注射后紫花前胡素的药动学特征研究。方法 大鼠血浆样本采用乙腈沉淀法去除蛋白。使用地西泮作为内标,UPLC BEH C₁₈柱（2.1 mm×50 mm,1.7 μm）为分离柱,以乙腈-0.1%甲酸为流动相,进行梯度洗脱,流速为0.4 mL·min^-1,分析时间为4.0 min。用电喷雾离子源（ESI）,正离子检测,多反应监测方式进行定量分析,紫花前胡素m/z 329.0→229.0和内标m/z 285.1→193.3。结果 紫花前胡素在1~60 ng·mL^-1内线性关系良好,定量限为1 ng·mL^-1。日内、日间精密度RSD均<14%,准确度范围在88.5%~107.5%,回收率>93.3%,基质效应在89.3%~93.5%。结论 本方法具备灵敏、快速、选择性好的特点,可应用于紫花前胡素大鼠药动学研究。     

UPLC-MS/MS检测大鼠体内达卢生坦的血药浓度及其药动学研究

目的 建立一种快速、高灵敏度和高选择性的UPLC-MS/MS用于大鼠血浆中达卢生坦的测定。方法 通过蛋白沉淀法完成血浆样品处理。通过Acquity UPLC BEH C₁₈柱（2.1 mm×50 mm,1.7 μm）色谱柱,流动相为0.1%甲酸水-乙腈,流速为0.4 mL·min^-1。采用ESI⁺方式检测,扫描方式为多反应离子监测方式检测。结果 达卢生坦血药浓度在0.01~2.5 μg·mL^-1内线性关系良好（R²>0.999 6）,定量下限（LLOQ）为0.01 μg·mL^-1。血浆中的达卢生坦平均回收率为87.613%~97.115%,日内及日间精密度RSD<7.71%,基质效应RSD<9.34%。结论 该方法灵敏高,快速高效,能成功应用于大鼠口服10.0 mg·kg^-1达卢生坦后的药动学研究。     

Plasma Concentration Clamping in the Rat Using a Computer-Controlled Infusion Pump

We have developed a computer-controlled infusion pump to achieve rapidly and then maintain stable plasma thiopental concentrations in rats. Initially we derived the parameters of a triexponential pharma-cokinetic model for thiopental, administered as a brief infusion to 10 rats, using nonlinear regression and standard pharmacokinetic equations. These parameters were incorporated into the pharmacokinetic model of a computer-controlled infusion pump. In a second group of animals this device was used to maintain three consecutive target thiopental concentrations ranging from 5 to 100 µg/ml in a stepwise fashion. Arterial blood gases were kept normal through controlled ventilation when necessary. The plasma thiopental concentrations in this second group of animals were generally higher than the target concentrations. The bias in pump performance (median prediction error) was +25%, and the inaccuracy (median absolute prediction error) was 26%. We fit the parameters of a three-compartment model to the plasma thiopental concentrations observed in the second group of animals. This produced a second set of thiopental pharmacokinetic parameters with the unique characteristic of having been derived from a computer controlled infusion study. These parameters were tested prospectively with a computer-controlled infusion pump in a third group of animals. This second set of thiopental pharmacokinetic parameters performed better, with a median prediction error of 0% and a median absolute prediction error of 15%. This study shows that it is possible to achieve rapidly and maintain steady plasma thiopental concentrations in the rat. Our results suggest that it is feasible to derive robust pharmacokinetic parameters from unusual drug dosing approaches, such as employed by a computer-controlled infusion pump. The ability rapidly to clamp plasma drug concentrations at desired targets in small laboratory animals will facilitate research into the relationship of plasma and tissue concentration to drug effect.     

UPLC-MS/MS测定大鼠血浆中8-O-乙酰山栀苷甲酯浓度

目的 建立超高效液相串联质谱法快速测定大鼠体内8-O-乙酰山栀苷甲酯的浓度。方法 用乙腈沉淀蛋白方法处理血浆,色谱柱为ACQUITY UPLC BEH C₁₈柱(50 mm×2.1 mm,1.7 μm);流动相为乙腈-0.1%甲酸水,梯度洗脱,流速为0.4 mL·min^-1;用正离子多离子反应监测(MRM)扫描,内标为槲皮素。结果 血浆中8-O-乙酰山栀苷甲酯的线性范围为2.5~500 ng·mL^-1(r=0.997 9),最低定量限为0.5 ng·mL^-1。低、中、高3个浓度(3, 45和450 ng·mL^-1)的质控样品的日内、日间精密度RSD均<10%,3个浓度的相对回收率分别为(103.59±4.75)%, (98.68±4.62)%和(97.06±5.64)%。结论 该方法操作简便、快捷,灵敏度高,适于大鼠血浆中8-O-乙酰山栀苷甲酯浓度的测定及其药代动力学研究。     

Receptor Occupancy in Myocardium,Adrenal Cortex,and Brain by TH-142177, a Novel AT1 Receptor Antagonist in Rats,in Relation to Its Plasma Concentration and Hypotensive Effect

Purpose. To study the relationship between angiotensin II (All) receptor occupancy ex vivo in tissues plasma concentration and hypotensive effect of a novel All receptor antagonist, TH-142177 and losartan in rats. Methods. At 2, 8 and 24 hr after oral administration of TH-142177 and losartan in rats, All receptors in myocardium, adrenal cortex and cerebral cortex were determined by radioligand binding assay using [¹²⁵I]Sar¹,Ile⁸-AII. Plasma concentrations of both drugs and metabolite in rats were also measured using validated HPLC assays. Further, systolic blood pressure (SBP) in conscious renal hypertensive rats treated orally with TH-142177 and losartan were measured by using a tail cuff plethysmographic method. Results. Oral administration of TH-142177 (1.8 and 5.5 mol/kg) and losartan (6.5 and 21.7 mol/kg) in rats brought about dose-dependent decreases in [¹²⁵I]Sar¹,Ile⁸-AII binding sites (Bmax) in myocardium and adrenal cortex. The extent of receptor occupancy by both drugs in adrenal cortex was maximal at 2 hr later but that in myocardium at 8 hr later. Further, the receptor occupancy was more sustained in myocardium than adrenal cortex. The ex vivo binding affinity of TH-142177 for All receptors in these tissues was roughly three times higher than that of losartan. Also, cerebral cortical [¹²⁵I]Sar¹,Ile⁸-AII binding was significantly reduced by oral administration of losartan but not by TH-142177. The time course of All receptor occupancy by both drugs in adrenal cortex appeared to be in parallel with that of their plasma concentrations, while the time course in myocardium correlated with that of their hypotensive effects rather than plasma concentrations. Conclusions. TH-142177 produced a relatively selective and sustained occupancy ex vivo of All receptors in myocardium and adrenal cortex of rats with approximately three times greater potency than losartan. Its time course of myocardial receptor occupancy was in parallel with that of hypotensive effect rather than plasma concentration.     

Relationship Between Enoxacin and Ciprofloxacin Plasma Concentrations and Theophylline Disposition

Certain fluoroquinolone antibiotics affect theophylline (THEO) disposition by inhibition of its metabolism, yet no studies to date have investigated the relationship between fluoroquinolone plasma concentration and THEO pharmacokinetics. The effects of two fluoroquinolones, enoxacin (ENOX) and ciprofloxacin (CIPRO), have been studied in male Sprague-Dawley rats (n = 33–46) at steady state plasma concentrations of 0–33 mg · 1^–1, achieved by supplementing an intravenous bolus dose with a constant rate infusion. The effects of steady state ENOX and CIPRO plasma concentrations on the clearance of THEO determined after an intravenous bolus dose of 6 mg · kg^–1 were described using a competitive inhibition model. The model consisted of two components, one describing a residual component of THEO clearance, which was unaffected by fluoroquinolone, the other describing the non-linear reduction of THEO clearance by fluoroquinolone. The residual clearance estimated from the model was comparable to renal clearance for THEO in the rat. The potency of each fluoroquinolone was characterised by a Ki value, the concentration reducing THEO clearance by 50% of the maximum change. These values were 4.7 µM and 16.3 µM for ENOX and CIPRO, respectively. Thus, in this study, ENOX was found to be a more potent inhibitor of THEO clearance than CIPRO. The method allowed direct in vivo comparison of potency between different fluoroquinolones, as pharmacokinetic differences, such as clearance, volume of distribution and bioavailability, were designed out.     

Effect of Isoflurane Anesthesia on Antipyrine Pharmacokinetics in the Rat

Pharmaceutical Research -     

异氟醚和依托咪酯对重症肌无力患者胸腺切除术Bcl-2的影响

目的 探讨异氟醚和依托咪酯对重症肌无力患者胸腺切除术血清Bcl-2的影响。 方法 40例重症肌无力胸腺切除术患者,随机分为异氟醚组和依托咪酯组,每组20例。采用ELISA法检测患者术前、术后血清Bcl-2水平的变化。 结果 异氟醚组血清Bcl-2术后低于术前(P<0.01),依托咪酯组血清Bcl-2水平术后高于术前(P<0.01)。两组血清Bcl-2水平术前比较差异无统计学意义(P>0.05),术后血清Bcl-2水平依托咪酯组高于异氟醚组(P<0.01)。 结论 异氟醚用于重症肌无力患者麻醉可降低Bcl-2水平,而依托咪酯则升高Bcl-2水平,异氟醚可能比依托咪酯更适合用于重症肌无力患者胸腺切除术的麻醉。     

LC-MS/MS测定阿齐沙坦及其盐在大鼠血浆中的药动学研究

目的 建立液相色谱-串联质谱法测定大鼠血浆中阿齐沙坦及其盐的浓度并研究其药动学。方法 大鼠血浆样本以乙腈沉淀蛋白后,采用Eclipse Plus C₁₈色谱柱（50 mm×3.0 mm,1.8 μm）;流动相（乙腈：水=60：40）,流速为0.35 mL·min^-1,柱温为40℃;采用Agilent 6430三重四极杆串联质谱仪,离子化方式：电喷雾-正离子（API-ES）;监测方式：MRM;阿齐沙坦监测离子对457.3/233.1,缬沙坦监测离子对436.2/291.4,用作内标。SD大鼠灌胃给予阿齐沙坦1.0 mg·kg^-1及阿齐沙坦盐1.2 mg·kg^-1。结果 阿齐沙坦在5~30 000 ng·mL^-1内线性关系良好;回收率为85%~115%,精密度RSD在±15%内。阿齐沙坦盐大鼠体内主要动力学参数如下：AUC_{（0-24 h）}为（12.9±3.2）μg·mL^-1·h^-1,AUC_（0-∞）为（14.2±4.1）μg·mL^-1·h^-1,C_max为（3.8±0.3）μg·mL^-1,T_1/2为（13.4±0.5）h。阿齐沙坦的主要动力学参数如下：AUC_{（0-24 h）}为（8.1±2.6）μg·mL^-1·h^-1,AUC_（0-∞）为（9.7±3.1）μg·mL^-1·h^-1,C_max为（2.3±0.5）μg·mL^-1,T_1/2为（10.5±0.5）h。结论 本法经方法学验证,适用于大鼠血浆中阿齐沙坦及其盐的浓度测定,可用于阿齐沙坦及其盐大鼠体内药动学研究。     

UPLC-MS/MS检测大鼠血浆中阿帕替尼的浓度及其药动学研究

目的 采用UPLC-MS/MS建立快速检测大鼠血浆中阿帕替尼浓度的方法,并应用于药动学研究。方法 大鼠血浆样本用乙腈沉淀蛋白,液质联用技术检测浓度,流动相为乙腈-水（含0.1%甲酸）,梯度洗脱,流速为0.3 mL·min^-1,柱温40℃,内标为氯唑沙宗;质谱条件：电喷雾离子化源（ESI）,负离子监测模式,检测离子对阿帕替尼为m/z 396.2→210.0和m/z 396.2→158.0,氯唑沙宗m/z 168.0→132.0。结果 阿帕替尼和内标氯唑沙宗的保留时间分别为1.07 min和1.40 min,线性范围为10~2 000 ng·mL^-1（r²=0.993）,检测限为1 ng·mL^-1,准确度为90.65%~111.50%,基质效应为89.14%~104.65%,平均回收率>86%,日内、日间精密度RSD均<10%。常温下放置24 h、冻融2次和-80℃冻存30 d的RSD均<10%。药动学研究结果显示,大鼠单次灌胃阿帕替尼76.5 mg·kg^-1,AUC_（0-t）为（6 114.41±645.99）ng·mL^-1·h,CL_z/F为（12.21±1.08）L·h^-1·kg^-1,V_z/F为（75.70±38）L·kg^-1,T_1/2为（4.23±1.94）h,T_max为（2±0.71）h,C_max为（1 377.7±284.54）μg·L^-1。结论 该法操作简便,重复性好,准确可靠,适用于大鼠血浆中阿帕替尼的浓度检测及其药动学研究。     

Pharmacokinetics and First-pass Metabolism of Levomepromazine in the Rat

Abstract: The time course of the blood concentrations of levomepromazine and its two major non-polar metabolites in man were studied in the rat after single oral and intraarterial doses of levomepromazine hydrochloride. The blood levels of N-monodesmethyl levomepromazine were on average 179% of the levomepromazine levels after oral doses, but only 15% of the levomepromazine levels after intraarterial doses. The blood levels of levomepromazine sulfoxide, relative to the levomepromazine levels, were also generally higher after oral doses than after parenteral doses, on average 65% and 25%, respectively. Large interindividual variations were observed in the blood levels of levomepromazine and in the systemic availability of the drug after oral doses. The distribution phase lasted for about 8 hrs, the mean apparent volume of distribution was 16.6 l/kg, and the total body clearance was on average 12.3 ml/min. It is concluded that the rat provides a suitable model for the kinetics of levomepromazine in man, and that the sulfoxide and N-monodesmethyl metabolites of the drug are mainly formed by first-pass metabolism after oral doses in the rat, either in the liver or in the gut.     

New High-performance Liquid Chromatography-DAD Method for Analytical Determination of Arbutin and Hydroquinone in Rat Plasma

Natural substances present in herbal preparations should be carefully used because they can give toxic or therapeutic effects despite of their amount or the way of administration. The safety of products of vegetable origin must be assessed before commercialisation by monitoring the active ingredients and their metabolites. This study was therefore designed to identify and quantify arbutin and its metabolite hydroquinone, naturally present in Arctostaphylos uva-ursi (L.) Spreng plant in rat plasma, after an acute and subacute administration of aqueous arbutin solution in Wistar rats. For this purpose a reversed-phase high-performance liquid chromatography coupled with photodiode array detection was developed to assess the pharmacokinetic of arbutin and hydroquinone in plasma of female rats treated with aqueous arbutin solutions. The detection (arbutin: 0.0617 µg/ml and hydroquinone 0.0120 µg/ml) and quantification (arbutin: 0.2060 µg/ml and hydroquinone: 0.0400 µg/ml) limits were determined. At the arbutin concentration level of 10.7 µg/ml repeatability was 13.33% and its recovery 93.4±6.93%, while at the hydroquinone concentration level of 10.6 µg/ml repeatability was 11.66% and its recovery 92.9±7.75%. Furthermore the method was fully validated and the obtained data indicate that the new method provides good performances.     

高效液相-质谱法联用测定大鼠体内去甲基斑蝥素血药浓度

目的:建立大鼠体内去甲基斑蝥素的 HPLC-MS 分析方法。方法:选用烟尿酸为内标,血浆样品经乙腈沉淀蛋白处理。色谱条件为 Hypersil SAX 阴离子交换色谱柱(4.6mm×250mm,5μm),甲醇-水(25∶75,含2.5%甲酸)为流动相,流速0.5mL·min~(-1),采用 HPLC-MS检测系统,AP-ESI 负离子模式,质谱检测参数如下:AP-ESI 负离子模式;雾化压力276kPa;温度350℃;保护气流量8 L·min~(-1);毛细管电压3500V;裂解电压为90V(NCTD)和120V(内标);SIM 检测,NCTD m/z185(M+H_2O-H)、烟尿酸m/z 179(M-H)。结果:血浆中去甲基斑蝥素检测方法的线性范围为0.2-20μg·mL~(-1),最低检测限可达2ng·mL~(-1)。血浆中去甲基斑蝥素的平均回收率为96.7%-100.3%,日内、日间 RSD 均小于8%。结论:本法灵敏、准确、选择性高,可用于去甲基斑蝥素的药代动力学研究。     

The Relationship Between Rat Intestinal Permeability and Hydrophilic Probe Size

Purpose. The relationship between rat intestinal permeability (P_app) of a range of hydrophilic probe molecules and probe geometry was examined. Methods. Molecules studied included mannitol, the polyethylene glycols (PEGs) 400, 900, and 4000, the dextran conjugated dye Texas Red^® (MW 3000) and the polysaccharide inulin (MW 5500). Molecular surface area, volume and cross-sectional diameter for each probe were determined from computer models. The effect of the bile salt sodium cholate, and bile salt: fatty acid mixed micelles on probe intestinal permeability was also studied. Results. Of the size parameters tested, cross-sectional diameter correlated best with log intestinal permeability. The data was fitted to a relationship of the form P_app = P⁰ _app exp(–Kr_ca) where r_ca is the molecular cross sectional radius, P⁰ _app and K are constants. Estimates of equivalent pore radii (R) were also made; the use of r_ca giving the most reasonable estimate of R. Absorption of all probes was enhanced by both simple and mixed micellar systems. Conclusions. For large hydrophilic probes, and possibly protein drugs, cross sectional diameter is a more important size parameter than volume based values for evaluating size-related retarded absorption. The relationship established may be used as a tool to assess absorption enhancement potential of excipients.     

Modeling Circadian Rhythms of Glucocorticoid Receptor and Glutamine Synthetase Expression in Rat Skeletal Muscle

Purpose The circadian rhythm of endogenous corticosterone (CS) may produce fluctuations of downstream gene expression in normal rats. This study examined changes in glucocorticoid receptor (GR) and glutamine synthetase (GS) expression in rat skeletal muscle in relation to plasma CS over a 24-h period. Methods Fifty-four normal male Wistar rats were sacrificed at 18 time points (n = 3) over 24 h. Plasma CS concentrations and gastrocnemius muscle GR and GS mRNA and GS activity were measured. Results The circadian rhythm of plasma CS was captured by a two-harmonic function. The expression of GR and GS mRNA and GS activity follow a circadian rhythm in normal rat skeletal muscle. GR mRNA reaches a trough at 4 h after the peak of plasma CS and it fluctuates between 0.55 and 0.9 fmol g tissue⁻¹. GS mRNA and activity reach peaks at 6 and 12 h after the endogenous CS peak. GS mRNA oscillates between 3 and 6 fmol g tissue⁻¹, whereas GS activity fluctuates between 17 and 23 μmol min⁻¹ g protein⁻¹. Mechanistic receptor/gene-mediated pharmacodynamic models were applied to describe the temporal patterns of GR mRNA, GS mRNA, and GS activity within the circadian cycle. Conclusions The integrated models were able to capture the circadian expression patterns of plasma CS, and GR and GS in normal rat skeletal muscle showing a dependence of tissue gene expression on plasma CS.