and
, n=8, weighing 11.4 kg±1.2 kg, aged 8-10 months) were purchased from
Shanghai Institute of Xingang Experimental Animal Center.
Shi SJ et al / Acta Pharmacol Sin 2003 Oct; 24 (10): 1011-1015
SHI Shao-Jun2, CHEN Hui, GU Shi-Fen, ZENG Fan-Dian
Department of Pharmacology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
1 Project supported by the Scientific Research Foundation of Committee of Science and Technology of Hubei Province. No 991P1609.
2 Correspondence to Dr SHI Shao-Jun. Department of Pharmacy, Xiehe Hospital Affiliated to Tongji Medical College, Wuhan 430022, China. E-mail sjshi1@163.com.
Received 2002-11-01 Accepted 2003-01-21
KEY WORDS daurisoline; dauricine; pharmacokinetics; pharmacodynamics
ABSTRACT
AIM: To study the combined pharmacokinetic-pharmacodynamic (PK-PD) model of daurisoline and dauricine, and compare their effects on cardiac electrophsiology, blood pressure, and hemodynamics in beagle dogs. METHODS: The plasma drug concentration was determined by the reversed-phase HPLC method and the effects on cardiac and hemodynamics were recorded by polygraph. The pharmacokinetic and PK-PD model parameters were calculated. RESULTS: The pharmacokinetics were best fitted to a two-compartment open model, and the relationship between effect and effect compartment concentration of both drugs could be represented by the sigmoid-Emax model. There were no significant differences in main pharmacokinetics and PK-PD parameters between the two drugs. CONCLUSION: No statistically different kinetic disposition characteristics and potencies of inhibitory effects on myocardial function of daurisoline and dauricine were found in beagle dogs.
INTRODUCTION
The combined pharmacokinetic-pharmacodynamic (PK-PD) model builds the bridge between these two classical disciplines. It can provide a more rational basis for dosage individualization and may thus guide applied pharmacotherapy to a higher level of performance[1].
Daurisoline (DS) and dauricine (Dau), the bisbenzyltetrahydroisoquinoline (BBI) alkaloids, were isolated from the root of Menispermum dauricum DC. Their anti-arrhythmic effects and mechanisms had been demonstrated in our laboratory[2-4]. The previous studies have revealed that DS and Dau prolonged action potential duration (APD) in ventricular myocytes in a use-dependent manner[5-7], which make them to be the very promising anti-arrhythmic agents. The present study was to construct the combined PK-PD model for both drugs, and compare their disposition characteristics and effects on cardiovascular system in beagle dogs.
MATERIALS AND METHODS
Reagents DS and Dau with purity >99 % were provided by Institute of Clinical Pharmacology, Tongji Medical College. Acetonitrile, methanol, and dichloromethane were of HPLC grade. Other reagents were of analytical grade.
Beagle dogs (and
, n=8, weighing 11.4 kg±1.2 kg, aged 8-10 months) were purchased from
Shanghai Institute of Xingang Experimental Animal Center.
Chromatography The HPLC system consisted of a solvent pump (Merck-Hitachi L-6000, Japan), a UV-detector (Shimadzu, Japan) operated at 284 nm, a column (Shimadzu ODS, 5 µm, 150 mm×4 mm) were protected with a guard column packed with the same material. The column was kept at room temperature. The mobile phase was acetonitrile-water-triethylamine (18:82:0.28), plusing phosphoric acid to pH 3.0, at 1.0 mL/min. The limit of quantitation (LOQ) was 50 µg/L of plasma, and the intra- and inter-assay coefficient of variation were less than 10 %. The absolute and relative recoveries were above 80 % and 85 %, respectively. The HPLC chromatograms of DS and Dau in plasma were shown in Fig 1.
Fig 1. Chromatogram of blank plasma (A), blank plasma spiked with DS and its IS (B), blank plasma spiked with Dau and its IS(C), plasma sample after iv DS (D), and plasma sample after iv Dau (E). 1: DS; 2: Dau; IS: internal standard.
Sample preparation IS 10 µL, acetonitrile 0.5 mL, dichloromethane 4 mL, and plasma 1 mL was mixtured. The mixture was vortexed for 5 min, then centrifuged at 3000 r/min for 15 min. The organic phase was transferred to a centrifuge tube. This procedure was repeated after addition of 2 mL dichloromethane. The organic phase was evaporated to dryness at 40 ºC under a nitrogen stream. The residue was reconstituted in 200 µL of mobile phase, and then 20 µL was analyzed by HPLC.
Measurement of myocardial function After the beagle dogs were anesthetized with sodium pentobarbital (30 mg/kg, iv) a canula was advanced into the left ventricle through the right common carotid artery. And the canula was connected to a pressure transducer which was connected to an amplifier and polygraph. The right femoral artery was canulated to measure the blood pres sure wave. ECG ( lead II) was observed simultaneously. After iv injection of DS (n=4) or Dau (n=4) to beagle dogs, the ECG, BP, and LVP signals were recorded. Blood samples were taken before dosing and at 2, 5, 10, 15, 20, 30, 45 min, and 1, 1.5, 2, 3, 4, 6, 8 h after dosing.
PK-PD model The effect compartment originally proposed by Sheiner is modeled as a additional hypothetical compartment linked to central compartment by a first-order process[8]. But the compartment receives negligible actual mass of drug. Hence, the exponential term for the effect compartment does not enter into the pharmacokinetic solution for the mass of drug in the body (Fig 2).
Fig 2. Effect compartment model in association with a traditional two-compartment model after iv input. 1, 2, and E represent central, peripheral, and effect compartment respectively.
For two-compartment model with an iv input, the drug concentration in plasma (C1) and effect (Ce) compartment can be expressed as follows:
Where 
was distribution rate constant,
was elimination rate constant,
K1e was transfer rate constant from central compartment to
effect compartment, and Ke0 was the rate constant for drug
removal from effect compartment.
The inhibitory effects on myocardial function were related to the effect compartment concentration. The relationship between the effects and effect compartment concentration of both drugs can be represented by the sigmoid-Emax model.
Where Emax was the maximal effect, EC50 was the
effect compartment concentration required to achieve 50 % of the maximal effect,
and 
was the Hill parameter that
allowed sigmoidicity of the concentrationeffect relationship. Ce
was the effect compartment concentrations.
Statistical analysis The pharmacokinetic parameters were calculated with 3P97 program. The PK-PD parameters were calculated by the PK-PD Parameters Estimate Program of Nanjing Military General Hospital. All data were expressed as mean±SD. Statistical difference was determined by t-test.
RESULTS
PK The results showed that plasma concentration existed a biexponential
decline following iv administration of DS or Dau 6 mg/kg. The pharmacokinetics
of both drugs were best fitted to a two-compartment open model. T1/2
for DS and Dau were (0.026±0.014) and (0.049±0.016) h and K12
for both test drugs were larger than K21. So these two test
drugs were distributed quickly. And both test drugs were eliminated quickly
from central compartment, the mean T1/2
were (3.1±
0.9) and (2.7±0.6) h, respectively. The Vd were (12±3)
and (16±3) L/kg, which were much larger than the actual body fluid volume
of dog.
Pharmacokinetic parameters T1/2
and T1/2 showed
no significant differences between two test drugs. It revealed that the distribution
and elimination processes of DS were similar to that of Dau. But C0
and AUC of DS were significantly higher than the corresponding values of Dau
(P<0.05). (Tab 1, Fig 3)
Tab 1. Pharmacokinetic parameters of dauricine (Dau) and daurisoline (DS) after iv 6 mg/kg in beagle dogs. n=4. Mean±SD. aP>0.05, bP<0.05, cP<0.01 vs DS.
Fig 3. Mean plasma concentration-time curves of DS and Dau after iv 6 mg/kg in beagle dogs. n=4. Mean±SD.
PD After iv DS and Dau 6 mg/kg in beagle dogs, HR, LVSP, dp/dtmax, and SBP were decreased. But the maximum pharmacological effects of both drugs peaked at 10-15 min later than the maximum plasma concentration was observed. There was no direct correlation between pharmacological effects (E) and plasma concentrations (Cp), and a counterclockwise hysteresis loop existed between them. By means of effect compartment theory, the measured pharmacological effects were parallel to the effect compartment concentrations (Ce). The relationships between the effects and Ce were successfully characterized by the sigmoid-Emax model (Fig 4). It was in good agreement between the predicted effects and experimental effects.
No significant differences of Ke0, EC50,
Emax, and
on HR, BP, LVSP, and dp/dtmax between DS and Dau at
the same dosage were found (P>0.05, Tab 2).
Fig 4. Relationships between inhibitory effects on HR, SBP, LVSP, +dp/dtmax
and plasma drug concentration (A) or effect compartment concentration (B) after
iv daurisoline (
)
and dauricine (
) 6 mg/kg in
beagle dogs. Open arrows denote the counterclockwise hysteresis loop between
E and Cp (A) and the parallel relationship between
E and Ce (B).
Tab 2. Pharmacodynamic parameters after iv DS and Dau 6 mg/kg in beagle dogs. n=4. Mean±SD.
DISCUSSION
In the study, the hysteresis between effects and plasma drug concentrations indicated that there was equilibration processes between plasma and effect compartment. Hence, we successfully collapsed the hysteresis loops when using the effect compartment model.
The pharmacokinetic parameters revealed that both drugs were distributed quickly from central compartment to tissue and had a wide distribution in beagle dogs, which was due to their high affinity to tissues and organs. The main pharmacokinetic parameters of DS were similar to that of Dau, suggesting both drugs had the same process of pharmacokinetics.
Ke0 precisely characterized the temporal aspects of equilibration between Cp and effects, which governed the degree of lag. The smaller the value of Ke0 , the greater the drug hysteresis loop[9,10]. The results revealed that the equilibration process between plasma and effect compartment of DS were similar to that of Dau. Emax reflected the efficacy of drugs and EC50 characterized the potency of drugs[11]. Hence, their efficacy and receptor affinity were not statistically different.
In conclusion, no statistically different kinetic disposition characteristics and potencies of the inhibitory effects on myocardial function of DS and Dau were found in beagle dogs.
REFERENCES
