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To develop a model of visceral pain in rats using a behavioral approach. Cyclophosphamide (CP), an antitumoral agent known to produce toxic effects on the bladder wall through its main toxic metabolite acrolein, was used to induce cystitis.CP was administered at doses of 50, 100 and 200 mg./kg. i.p. to male rats, and their behavior observed and scored. The effects of morphine (0.5 to 4 mg./kg. i.v.) on CP-induced behavioral modifications were tested administered alone and after naloxone (1 mg./kg. s.c.). In addition, 90 minutes after CP injection, that is, at the time of administration of morphine, the bladder was removed in some rats for histological examination. Finally, to show that the bladder is essential for the CP-induced behavioral modifications, female rats also received CP at doses of 200 mg./kg. i.p. and of 20 mg. by the intravesical route, and acrolein at doses of 0.5 mg. by the intravesical route and of 5 mg./kg. i.v.CP dose-relatedly induced marked behavioral modifications in male rats: breathing rate decrease, closing of the eyes and occurrence of specific postures. Morphine dose-dependently reversed these behavioral disorders. A dose of 0.5 mg./kg. produced a reduction of almost 50% of the behavioral score induced by CP 200 mg./kg. This effect was completely prevented by pretreatment with naloxone. At the time of administration of morphine, histological modifications of the bladder wall, such as chorionic and muscle layer edema, were observed. In female rats, CP 200 mg./kg. i.p. produced the same marked behavioral modifications as those observed in male rats. Administered at the dose of 20 mg. intravesically, CP did not produce any behavioral effects, whereas acrolein at 0.5 mg. intravesically induced behavioral modifications identical to those under CP 200 mg./kg. i.p., with the same maximal levels. Conversely, acrolein 5 mg./kg. i.v. did not produce any behavioral effects at all.Overall, these results indicate that this experimental model of CP-induced cystitis may be an interesting new behavioral model of inflammatory visceral pain, allowing a better understanding of these painful syndromes and thus a better therapeutic approach to them.

Kinetics of amitriptyline (AMI), its demethylated metabolites nortriptyline (NOR) and demethylnortriptyline (DM-NOR), and its hydroxylated metabolites, the E and Z isomers or 10-hydroxy-amitriptyline (E- and Z-10-OH-AMI) and of 10-hydroxynortriptyline (E- and Z-10-OH-NOR) were studied in plasma and brain from Swiss CD1 mice after six successive intraperitoneal injections of amitriptyline (10 mg/kg) administered every elimination half-life time (t1/2 = 3.1 h) to obtain the steady state. In these conditions, AMI was metabolised rapidly. Compared with acute administration, hydroxylation reactions were saturated by the repeated AMI injections and demethylation became preponderant both in plasma and brain. Thus, plasma levels of demethylated metabolites, NOR and DM-NOR, increased (49% and 13% of total AUC against 22% and 7% in acute conditions, respectively), while levels of AMI and its hydroxylated metabolites, 10-OH-AMI and 10-OH-NOR, decreased (8%, 2.5% and 27.5% against 17%, 8% and 46% in acute conditions, respectively). Likewise in brain tissue, when AMI was repeatedly administered, NOR and DM-NOR increased (62% and 22% against 29% and 11%, respectively) while AMI and 10-OH-AMI decreased (11.5% and 1% against 47% and 9%, respectively). These differences may account for modified pharmacological effects seen after half-life repeated administration of AMI since demethylated metabolites exert a more marked inhibiting effect than AMI on noradrenaline reuptake.

The fate of amitriptyline (AMI) and its demethylated and hydroxylated metabolites was studied in Swiss CD1 mice, after acute intraperitoneal injection of AMI (20 mg/kg). Levels of each compound were determined to establish pharmacokinetic parameters in plasma and brain. Absorption and elimination of AMI were rapid (tmax = 0.37 h and 0.42 h, and t1/2 = 3.2 h and 3.6 h in plasma and brain, respectively). In plasma, 10-OH-nortriptyline was the main metabolite (46% of AUC) and 10-OH-amitriptyline reached significant levels but only during the first hour. In brain, AMI (43% of total AUC), nortriptyline (NOR) (29%) and demethylnortriptyline (DM-NOR) (11%) were the most abundant compounds, possibly through high blood-brain barrier transfer and/or marked intracerebral demethylation. Brain OH-metabolite levels were much lower. Knowledge of kinetic parameters and metabolism of AMI can help in the evaluation of pharmacological activity.

The influence of tolcapone, an inhibitor of catechol-O-methyl transferase, was evaluated on the disposition of apomorphine, a dopamine agonist used to treat Parkinson's disease, to explain a previously observed increase of duration of the effect of apomorphine associated with tolcapone. Sampling was performed in rats before and at different times after administration of apomorphine and following that of tolcapone or saline. Both in plasma and striatum, times to reach maximal-concentration and maximal concentrations did not significantly differ between the two groups but the elimination half-life times and areas under the curve were significantly greater following tolcapone treatment than in the saline group. These results show that tolcapone can increase plasma apomorphine bioavailability by modifying its liver catabolism.

Biotransformation of amitriptyline (AMI) was studied at different intervals in freshly isolated hepatocytes from healthy or streptozocin-induced diabetic rats in order to investigate the influence of the diabetic state. Levels of free and conjugated AMI, demethylated and hydroxylated metabolites, were assessed by HPLC analysis. In hepatocytes isolated from diabetic rats, AMI was less completely metabolized and the demethylation reaction became more important than in non-diabetic rat hepatocytes. Although the proportions of hydroxylated metabolites decreased in diabetic rats, it always remained predominant. Furthermore, glucuronidation of metabolites was greater, especially for (Z)-10-hydroxynortriptyline in diabetic animals.

Plasma and brain levels of amitriptyline (AMI), its demethylated and hydroxylated metabolites were determined after acute IP administration of AMI (20 mg/kg) in streptozocin-induced diabetic Sprague-Dawley rats. Results showed 1. 1. in plasma: rapid AMI absorption, but slow elimination; the proportion of AMI similar to those of the rest of compounds; the proportion of its demethylated metabolite, nortriptyline, 1.8-fold higher than that of 10-hydroxy-nortriptyline. 2. 2. in brain: the proportions of AMI and nortriptyline were 9.5- and 2.6-fold higher respectively, than those of whole hydroxylated metabolites, which represented 7.4% of the total amount.