and size of the milky spots. Moreover, with this approach, the peritoneum is exposed long term to the PD fluid, since ;18 h w5x are needed for the fluid to be ...
Nephrol Dial Transplant (2001) 16: 672±674
Rat models in peritoneal dialysis Robert H. J. Beelen, Liesbeth H. P. Hekking, Mammad Zareie and Jacob van den Born Department of Cell Biology and Immunology, Faculty of Medicine, Vrije Universiteit, Van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands
Abstract Background. It is widely accepted that the currently used dialysis solutions are not biocompatible with the peritoneal membrane. Therefore, animal studies have been performed to study different aspects of peritoneal dialysis. However, representative models mimicking the human situation are not yet available. Methods. The effect of a single injection of peritoneal dialysis (PD) ¯uid on the cellular composition was studied. Thereafter, the effect of a single injection of PD ¯uid on bacterial clearing was tested over time. Finally, an in vivo rat model was established to study the effects of long-term exposure to PD ¯uid on the peritoneal membrane and the local host defence (peritoneal cells). Results. In the rat model, long-term daily exposure is possible. The `drop-out' after 9±10 weeks on the most commonly used PD ¯uid Dianeal 3.86%, however, is ;50% due to omental wrapping. In the remaining study group, large differences were observed (as compared with controls), especially with respect to morphological parameters. Conclusions. The rat peritoneal continuous exposure model seems to have potential for intervention studies, since it uses no additions, no antibiotics and no omentomectomy, and gives continuous long-term exposure to PD ¯uid. However, problems still remain: `drop-out' is quite often seen and this non-uraemic exposure model does not totally mimic the situation present in continuous ambulatory PD patients. Keywords: CAPD; PD models; peritoneal dialysis ¯uids; rat
Correspondence and offprint requests to: Robert H. J. Beelen, Department of Cell Biology and Immunology, Faculty of Medicine, Vrije Universiteit, Van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands. #
Introduction It is now well accepted that the currently used dialysis solutions are not biocompatible with the peritoneal membrane w1x. The development of new and more physiological peritoneal dialysis (PD) solutions is therefore one of the major research focuses (for a review, see w2x). In order to test more biocompatible ¯uids, there is a need for in vivo animal models for preclinical evaluation w3x; this eventually should include a proper uraemic model w4,5x. Here we discuss past and present studies in rat PD models from our group, especially with respect to the potential and problems, relevant to clinical PD.
Results and discussion Previously, we showed w6x that a single acute administration of 10 ml of PD ¯uid into the peritoneal cavity of the rat induced an acute in¯ammatory state, in comparison with the minor effects observed after saline infusion. The effect of prior injection of PD ¯uid on in vivo bacterial clearing showed that glucose concentration in the PD ¯uid impaired the antibacterial host defence. Moreover, the effect of the dwell time (time between PD ¯uid administration and bacterial infection) was also important (negative correlation with dwell time) w7x. To study the long-term effect of dialysis ¯uids on the peritoneal cell layers and the local defence mechanism, an in vivo rat model was developed w8x. Mini vascular access ports were implanted subcutaneously in the neck of rats, and an attached catheter was tunnelled subcutaneously towards the abdomen and inserted into the peritoneal cavity. This model allows the assessment of not only immune parameters w8x, but also the morphological±functional relationship w9x after longterm exposure (up to 20 weeks) to various dialysis solutions. The potential of this model is obvious. No omentomectomy was performed; therefore, the morphological changes in the state of this important immunological organ w10x can also be analysed. As can been seen in
2001 European Renal Association±European Dialysis and Transplant Association
Rat models in peritoneal dialysis
Fig. 1. Omentum of rat after 10 weeks daily exposure to Dianeal showing a strong increase in the number and size of milky spots.
Fig. 2. Percentage of catheters kept open in three separate experiments on Dianeal daily for 9±10 weeks (A, ns14; B, ns15; C, ns16). The `drop-out' rate is ~50%.
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Figure 1, there is a strong increase in both the number and size of the milky spots. Moreover, with this approach, the peritoneum is exposed long term to the PD ¯uid, since ;18 h w5x are needed for the ¯uid to be absorbed, and every 24 h new PD ¯uid is administered. No antibiotics, heparin or further additions were given. Some problems still remain. (i) As seen in Figure 2 in three separate experiments (A, ns14; B, ns15; C, ns16), after 9±10 weeks of daily peritoneal exposure to the most commonly used PD ¯uid, Dianeal 3.86%, there is a `drop-out' of ;50% of the animals (40±60% in the three different experiments). (ii) This `drop-out' is due mostly to omental wrapping (Figure 3) around the tip of the catheter, which made it impossible to continue the daily injection of PD ¯uid in these animals. Zweers et al. w9x noted a much lower `drop-out', but in their approach heparin was added to the PD ¯uid. (iii) The animals were not uraemic, unlike those described by Lameire et al. w5x. However, in their studies, a large number of animals died before longterm studies could be completed. The combination of a uraemic model w5x with the developed chronic exposure model w8x would be an attractive alternative and presently is being studied. (iv) The daily exposure model unfortunately does not allow collection of ef¯uent. Finally, with the potential and problems in mind, it has been possible to compare the effects of some PD ¯uids in vivo on various parameters in our model (bacterial clearing, see Hekking et al. w8x; morphology of the peritoneum, see Zweers et al. w9x). Beside the data given in this present overview (especially focused on the `drop-out' and the changes in the omentum), these studies have shown that relevant changes with respect to ®brosis, neo-vascularization, bacterial killing and peritoneal permeability characteristics can be obtained. Future studies will investigate the exact differences between different PD ¯uids and in particular will unravel the role of pH, glucose and glucose degradation products in the induction of these changes. We conclude that, within given limitations, this exposure model is suitable for studying some effects relevant to the clinical PD setting and offers the possibility for future intervention studies. Acknowledgements. This work has been supported, in part, by the Dutch Kidney Foundation.
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Fig. 3. `Drop-out' rat (closed catheter) showing omental wrapping around the catheter (arrows).
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