Comparison of plasma disposition of alkaloids after lupine challenge in cattle that had given birth to calves with lupine-induced arthrogryposis or clinically normal calves

OBJECTIVE

To compare plasma disposition of alkaloids after lupine challenge in cattle that had given birth to calves with lupine-induced arthrogryposis and cattle that had given birth to clinically normal calves and determine whether the difference in outcome was associated with differences in plasma disposition of anagyrine.

ANIMALS

6 cows that had given birth to calves with arthrogryposis and 6 cows that had given birth to clinically normal calves after being similarly exposed to lupine during pregnancy.

PROCEDURES

Dried lupine (2 g/kg) was administered via gavage. Blood samples were collected before and at various time points for 48 hours after lupine administration. Anagyrine, 5,6-dehydrolupanine, and lupanine concentrations in plasma were measured by use of gas chromatography. Plasma alkaloid concentration versus time curves were generated for each alkaloid, and pharmacokinetic parameters were determined for each cow.

RESULTS

No significant differences in area under the plasma concentration versus time curve, maximum plasma concentration, time to reach maximum plasma concentration, and mean residence time for the 3 alkaloids were found between groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Because no differences were found in plasma disposition of anagyrine following lupine challenge between cattle that had given birth to calves with arthrogryposis and those that had not, our findings do not support the hypothesis that between-cow differences in plasma disposition of anagyrine account for within-herd differences in risk for lupine-induced arthrogryposis.

Extremely slow metabolism of amitriptyline but normal metabolism of imipramine and desipramine in an extensive metabolizer of sparteine, debrisoquine, and mephenytoin

A 34-year-old man with bipolar manic depressive illness suffered from severe adverse effects during treatment with amitriptyline, 50 mg/day. It was subsequently shown that the patient was a slow metabolizer of amitriptyline. However, he tolerated a dose of 200 mg of imipramine/day, which was necessary in order to reach a therapeutic level of about 900 nM for imipramine plus desipramine. Since both antidepressants are subject to the genetic sparteine/debrisoquine oxidation polymorphism, the patient was phenotyped with sparteine. The test performed during paroxetine treatment indicated that the patient was a poor metabolizer. Subsequent tests performed during a drug-free period, however, showed the patient to be an extensive metabolizer, with a sparteine metabolic ratio (MR) of 1.7 and 2.8 and debrisoquine MR of 2.3. It was subsequently shown that paroxetine is a potent, competitive inhibitor of 1'-hydroxybufuralol formation in a human liver microsome preparation (K1 approximately 800 nM). This patient thus illustrates two problems: (a) the erroneous phenotyping due to concurrent medication, and (b) the existence of a very slow amitriptyline elimination apparently not related to the sparteine/debrisoquine oxidation polymorphism.

Subnanogram GC/NPD method for the determination of sparteine in biological fluids

A gas chromatographic method is presented for identification and quantification of sparteine in biological fluids using cyclizine as an internal standard. No derivation is necessary and after a single alkaline extraction, GC analysis of sparteine is achieved in less than 8 min. A subnanogram limit of detection is allowed by the use of a nitrogen phosphorous detector (NPD). This method is simple, reproducible, selective, and applicable in both clinical and pharmacokinetic studies.

Sparteine oxidation polymorphism: phenotyping by measurement of sparteine and its dehydrometabolites in plasma

Phenotyping of the ability to oxidize sparteine was markedly facilitated by analyzing sparteine and dehydrosparteines in a single plasma sample by gas chromatography. The definitive identification of extensive and poor metabolizers was possible only 90 min after ingestion of 100 mg sparteine sulphate. In 121 healthy volunteers determination of the plasma level ratio was compared to the established determination of the metabolic ratio in urine. In each subject the alloted phenotype was the same by both methods. Plasma and urine analysis showed 9.9% of poor metabolizers.

Non-linear pharmacokinetics of sparteine in the rat

In rats, blood concentrations of sparteine (SP) and relative concentrations of sodium borohydride-reducible metabolite following intra-arterial (i.a.) and portal venous administration of SP-sulphate were estimated up to 200 min. In 24 hr urine, unchanged SP was quantitated. Borohydride-reducible metabolite was measured as the difference in SP concentrations before and after reduction. Administration of SP in a dose of 50 mg/kg SP-sulphate i.a. revealed a blood concentration-time profile which did not allow characterization of the terminal half-life or systemic clearance. Therefore, the dose over the area under the curve up to 120 min after administration, CL0-120app, was defined as an apparent average clearance value over the time interval studied. After a dose of 50 mg/kg the CL0-120app was 34.8 +/- 5.9 ml/min/kg when administered i.a. and 80.4 +/- 7.5 ml/min/kg when administered via the portal vein, thus affording an estimate of 0.64 +/- 0.12 for the hepatic extraction ratio. A possible biliary excretion and enterohepatic circulation was studied in rats with a bile fistula. Although SP levels in blood were lower than in control rats, no SP was excreted in the bile and excretion of SP in urine was even slightly higher, which renders circulation of SP itself unlikely. About 25% of the dose was recovered in 180 min bile as borohydride-reducible metabolite, but the urinary excretion of borohydride-reducible metabolite was not changed. The gradual levelling-off of blood concentration versus time curves may partly be explained by the formation of reactive intermediates in the course of metabolism, which inactivate P-450. In support of this, the intrinsic clearance of orally administered hexobarbital (25 mg/kg) was determined 5 and 50 min after i.a. administered SP-sulphate (50 mg/kg), and decreased from 343 +/- 18 to 220 +/- 36 ml/min/kg (p less than 0.05).

Pharmacokinetics of N-propylajmaline in relation to polymorphic sparteine oxidation

In order to determine whether the metabolism of the antiarrhythmic drug N-propylajmaline is under the same genetic control as sparteine metabolism, the pharmacokinetics of this antiarrhythmic drug were studied in a groups of six extensive and four poor metabolizers of sparteine. Pronounced differences in terminal half-life, total plasma clearance, metabolic clearance and urinary excretion of N-propylajmaline were observed between extensive and poor metabolizers. A close relationship between the total clearance and metabolic clearance of N-propylajmaline and sparteine could be demonstrated. Clinically available N-propylajmaline is a 55% to 45% mixture of the i- and n-diastereomers. The extensive metabolizers exhibited stereoselective metabolism; the i-diastereomer was preferentially metabolized. Poor metabolizers were characterized by a loss of this stereoselective metabolism. Five subjects were treated for 7 days with a daily N-propylajmaline dosage of either 60 mg or 20 mg. Since a close relationship between the clearance of N-propylajmaline and the metabolic ratio of sparteine had been observed after single dosing the metabolic ratio of sparteine was used to predict N-propylajmaline steady-state plasma concentrations during multiple dosing. Only in two extensive metabolizers with a metabolic ratio less than 0.4 predicted and observed, steady-state plasma concentrations were in good agreement. In the other three subjects observed steady-state plasma concentrations were appreciably higher than predicted. In these three subjects metabolic N-propylajmaline clearance decreased indicating saturation N-propylajmaline metabolism during multiple dosing. The data indicate that N-propylajmaline metabolism is subject to a genetic polymorphism controlled by the sparteine/debrisoquine gene locus.

Influence of the defective metabolism of sparteine on its pharmacokinetics

Sparteine is metabolized by N1-oxidation, which in some subjects is defective. The defect has a pronounced effect on the kinetics of the drug. In nonmetabolisers elimination of sparteine proceeds entirely via renal excretion by a capacity-limited process, 99,9% of the dose being excreted as unchanged drug. In metabolisers the drug is mainly eliminated by metabolic degradation. Pronounced differences in beta-phase half-life and total plasma clearance were observed between metabolisers (156 min; 535 ml . min-1) and nonmetabolisers (409 min; 180 ml . min-1).