A catheter system for long-term intravenous infusion in unrestrained rats

Chronic intravenous model for studies of drug (Ab)use in the pregnant and/or group-housed rat: an initial study with cocaine

Animal models for studying the developmental effects of maternal drug abuse are often based on chronic exposure of the pregnant rat. The suitability of animal models, however, has been constrained by the availability of an appropriate route of administration. The commonly employed SC and PO routes of administration fail to mimic the rapidly peaking pharmacokinetic profile observed in humans with licit (e.g., nicotine) and illicit (e.g., cocaine, methamphetamine) drugs abused via inhalation or i.v. injection. The present study provides a method for the routine use of an i.v. administration model in pregnant and/or group-housed rats. Prior to mating, young adult female Sprague-Dawley rats were anesthetized (ketamine/xylazine) for catheterization. A sterile Intracath i.v. catheter (22 ga., Becton/Dickinson) with a Luer-lock injection cap (Medex) was cut to approximately 8 cm and used as a SC dorsally implanted port for chronic i.v. injections. The distal end of the catheter was inserted into the jugular vein and threaded centrally. Catheter patency was maintained by daily flushing with 0.2 ml of heparinized saline. Following 1 week of surgical recovery, the mean (median)number of estrus cycles to impregnation was 2.5(2). The mean (+/- SEM) duration of catheter patency was 36.6 +/- 1.2 days and was in excess of 30 days for all animals (n = 22). Cocaine at a dose of 3 mg/kg (GD8-14 x 1/day, GD15-20 x 2/day) had no significant effect on dam weight gain, gestation length, litter size, sex ratio, or birth weight. In sum, a subcutaneously implanted port provides a procedure for the routine i.v. administration of drugs to pregnant and/or group-housed rats which avoids (a) the use of anesthesia/surgery during pregnancy, (b) the stress (restraint and/or thermal dilation) associated with tail vein injection, (c) the difficulties of mating and single housing associated with tethered i.v. catheters, and (d) in the case of cocaine, precludes the potential confounds of any drug-induced non-i.v. parenteral lesions.

Comparison of two methods for determining the toxicokinetics of fluazifop-butyl after intravenous dosing in rats

1. We have described and compared the use of two blood sampling techniques to measure the kinetics of fluazifop-butyl, a selective herbicide. Following intravenous administration of radiolabelled compound, blood samples were collected from female rats either by tail vein puncture or from chronically implanted catheters inserted in tethered rats. Urine samples were also collected from tethered animals. 2. Both techniques indicate that fluazifop-butyl is rapidly eliminated from blood into urine (t(1/2)3-4.5 h) and the overall blood concentration profiles were comparable between the two methods. However, by using cannulated rats, kinetic data were obtained from individual animals, providing evidence of inter-animal variation and allowing compartmental and statistical analysis. 3. The tethered rat technique is relatively simple and reliable. Compared to tail vein bleeding, results obtained from cannulated animals are more informative, providing comprehensive data from a small number of rats. It is therefore the preferred method for our kinetic based research studies using compounds known to exhibit multicompartmental elimination kinetics.

A freely moving and behaving rat model for the chronic and simultaneous study of drug pharmacokinetics (blood) and neuropharmacokinetics (cerebrospinal fluid): hematological and biochemical characterization and kinetic evaluation using carbamazepine

A freely moving and behaving rat model for the chronic and simultaneous study of drug pharmacokinetics (blood) and neuropharmacokinetics [cerebrospinal fluid (CSF)] is described. The blood (jugular vein) and CSF (cisterna magna) catheters employed are simple, reliable, and inexpensive. The blood catheter was made of soft and flexible Silastic tubing and sealed with heparin. The CSF catheter consisted of intersliding polythene tubing and interlocking Silastic tubing, which allowed maneuverability within the cisternal magna space and thus prolonging patency for chronic studies. Both catheters were well tolerated by the animals, and the postoperative success rate was 80%-100%; after 8 days 80%-85% of catheters were still patent. Using a sampling protocol considered suitable for kinetic studies, we determined numerous biochemical and hematological parameters and compared them with those values obtained postsurgically and in control rats. The parameter changes associated with the sampling protocol did not affect the kinetics of the commonly prescribed antiepileptic drug carbamazepine and its primary pharmacologically active metabolite carbamazepine-10, 11-epoxide. Therefore, the model can be used to study the interrelationship between drug kinetics at central and peripheral sampling sites and mechanism(s) of drug action.

A reliable technique for chronic carotid arterial catheterization in the rat

A reliable and simple method for cannulating the carotid artery of rats is described. The rat was anesthetized with halothane. The right carotid artery located between the omohyoideus and sternohyoideus muscles was exposed through a 2-cm ventral neck incision. The catheter was made of Silastic tubing and a monofilament line, which served as an obturator and internal support. The line was then filled with a viscous mixture of heparin, polyvinylpyrrolidinone and normal saline to prevent the formation of blood clots. The catheter was advanced through the carotid artery towards the heart by a predetermined distance (15-20 mm) depending on the size of the rat. The catheter was well tolerated by the rats and the success rate was 95%. Its patency lasted for at least 7 days postsurgery without any special maintenance care. With the described method one would be able to perform repetitive blood sampling and arterial blood pressure measurements in unanesthetized and unrestrained rats for prolonged period after catheterization.

Alterations in hepatic mitochondrial function during total parenteral nutrition in immature rats

To evaluate the effects of total parenteral nutrition (TPN) on hepatic mitochondrial function in immature rats, changes in hepatic energy charge levels and oxidative phosphorylation rates of hepatic mitochondria were studied along with the examination of serum chemical test. Male Wistar rats weighing 30 to 45 g were used and randomized into TPN (n = 8), enteral (n = 7), and control groups (n = 8). Parenteral and enteral groups were fed with TPN solution containing 19.3% dextrose, 3.19% amino acids, 1.05% fat emulsion, minerals and vitamins, and the control group with rat chow. The number of calories per kilogram per day was 550 x 1/4 on the 1st day, 550 x 1/2 on the 2nd, 550 x 3/4 on the 3rd, and 550 x 1 on the 4th day, based on the body weight on the 1st day. After the 5th day, 550 Kcal/kg/day was given, based on the body weight of the respective day. After 13-day feeding, hepatic energy charge (EC), phosphorylation rate (PR) of hepatic mitochondria and serum chemical examination were carried out. EC was 0.871 +/- 0.016 in the control group, 0.830 +/- 0.019 in the enteral, and 0.785 +/- 0.011 in TPN group (p less than 0.001, compared with control group). PR was 138.9 +/- 1.9, 133.0 +/- 6.7, 111.0 +/- 4.3, respectively, (p less than 0.05, compared with control and enteral groups). There was no difference between the three groups on SGOT, SGPT, and total bilirubin. TPN group showed a deterioration of hepatic phosphorylation rate and energy charge in spite of normal serum transaminase levels.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of prednisolone on the recirculation of peripheral blood lymphocytes in vivo

In humans and in laboratory animals, administration of a single does of glucocorticosteroids induces a rapid and transient decrease in the numbers of peripheral blood lymphocytes through a redistribution of circulating lymphocytes. This lymphocytopenic effect is an important factor in the immunosuppressive capacity of corticosteroids. We have investigated whether the redistribution is due to an increased influx of circulating lymphocytes from the blood into the lymphoid organs or to a decreased efflux from the organs. Fluoresceinated lymphocytes were injected intravenously in unrestrained normal and prednisolone-treated rabbits and the distribution curves in the peripheral blood were analysed on the basis of a two-compartment model (known from pharmacokinetic studies). In this way, it is shown that the rapid fall in peripheral blood lymphocyte numbers induced by prednisolone is due to a decreased efflux of circulating lymphocytes from the lymphoid organs. In addition, it is demonstrated that prolonged infusion of prednisolone leads to an altered distribution pattern of the circulating lymphocytes among the organs.

[Nitrogen balance in tumor and host in the animal model]

The importance of malnutrition as major cause of morbidity and mortality in cancer patients is well documented. It has been shown that nutritional therapy improves well-being and nutritional status of the patient, but the tumor can also be accelerated by hypercaloric nutrition. Our study does not confirm the induction of tumor growth. A high positive metabolic rate of the host lowers the tumor's growth rate and its tendency to spread. The retention of nitrogen in host increase with decreasing rate of energy and nutrition. Our results show that the tumor itself uses energy and nutrients from host cell catabolism and does not directly exploit exogenous nutrient substrates. It should not be forgotten that the animal model leads to specific changes affecting the energy and nutrient metabolism.

A simplified cannulation procedure for pharmacokinetic experiments in rats

A convenient, simplified method for cannulating the jugular vein of rats is described. The technique has been developed for use in pharmacokinetic experiments. The construction of the cannula has been simplified compared with previously described methods. In addition, a small and simple outlet device for the cannula is described which allows the connection of tubing for sampling at short time intervals or for short-term infusions (several hours). In order to reduce stress on the animal, the tubing can be disconnected during sampling at long time intervals, allowing free movement of the animal with only a very small external outlet device.