A Novel Rat Model of Vitamin D Deficiency: Safe and Rapid Induction of Vitamin D and Calcitriol Deficiency without Hyperparathyroidism

Vitamin D deficiency is associated with a range of clinical disorders. To study the mechanisms involved and improve treatments, animal models are tremendously useful. Current vitamin D deficient rat models have important practical limitations, including time requirements when using, exclusively, a vitamin D deficient diet. More importantly, induction of hypovitaminosis D causes significant fluctuations in parathyroid hormone (PTH) and mineral levels, complicating the interpretation of study results. To overcome these shortcomings, we report the successful induction of vitamin D deficiency within three weeks, with stable serum PTH and minerals levels, in Wistar rats. We incorporated two additional manoeuvres compared to a conventional diet. Firstly, the vitamin D depleted diet is calcium (Ca) enriched, to attenuate the development of secondary hyperparathyroidism. Secondly, six intraperitoneal injections of paricalcitol during the first two weeks are given to induce the rapid degradation of circulating vitamin D metabolites. After three weeks, serum 25-hydroxyvitamin D 3 (25D) and 1,25-dihydroxyvitamin D 3 (1,25D) levels had dropped below detection limits, with unchanged serum PTH, Ca, and phosphate (P) levels. Therefore, this model provides a useful tool to examine the sole effect of hypovitaminosis D, in a wide range of research settings, without confounding changes in PTH, Ca, and P

Improvement of a chronic rat model for peritoneal dialysis by using heparin-coated catheters

The use of silicone peritoneal catheters, connected to implanted subcutaneous mini vascular access ports, was an essential step in the development of a widely used rat model for peritoneal dialysis (PD). Despite the model's many advantages, it has one major disadvantage: a high drop-out rate because of omental wrapping of the silicone catheter. To investigate whether heparinization of the peritoneal catheter reduces the high drop-out rate in the model, we infused rats with conventional PD fluid through either a regular silicone catheter (PDF, n = 14) or a heparin-coated catheter (PDF-h, n = 15) daily for 5 weeks. Untreated rats served as a control group (control, n = 7). We used various peritoneal tissues for cellular and morphologic analysis by light and electron microscopy. We found a statistically significant, lower rate of drop-out in rats implanted with heparin-coated catheters (20%) than in rats implanted with regular silicone catheters (57%, p < 0.05). No significant differences were seen between the two treated groups with regard to the PD fluid-induced angiogenic response in omentum and mesentery. Likewise, instillation of PD fluid resulted in a similar cellular response (increased numbers of mast cells and milky spots in the omentum and mesothelial regeneration on the liver) in both groups regardless of heparin coating. Based on our results, we recommend the use of heparin-coated catheters for instillation of dialysis solutions in the chronic PD model in the rat

Peritoneal exposure model in the rat as a tool to unravel bio(in)compatibility of PDF

Patients treated with peritoneal dialysis (PD) are at risk for development of ultrafiltration failure and peritonitis. The relative unphysiologic composition of the currently used peritoneal dialysis fluids (PDF) is a major cause for the development of morphologic changes of the peritoneal membrane such as fibrosis and new vessel formation, ultimately resulting in ultrafiltration failure. In recent years, a major research focus has become the development of new and improved PDF. Typically, the first phase of biocompatibility testing of new PDF involves in vitro testing, using cell culture systems such as primary mesothelial cells or peritoneal macrophages. In vivo studies using animal models permit the analysis of biocompatibility under conditions that allow for cell-to-cell interactions and dynamic changes in solution composition that more closely mimic the clinical situation. In this paper, we will review the applicability of a peritoneal exposure model in the rat to study PDF biocompatibility-related issues

Improved biocompatibility of bicarbonate/lactate-buffered PDF is not related to pH

BACKGROUND: Chronic exposure to conventional peritoneal dialysis fluid (PDF) is associated with functional and structural alterations of the peritoneal membrane. The bioincompatibility of conventional PDF can be due to hypertonicity, high glucose concentration, lactate buffering system, presence of glucose degradation products (GDPs) and/or acidic pH. Although various investigators have studied the sole effects of hyperosmolarity, high glucose, GDPs and lactate buffer in experimental PD, less attention has been paid to the chronic impact of low pH in vivo. METHODS: Rats received daily 10 ml of either conventional lactate-buffered PDF (pH 5.2; n=7), a standard bicarbonate/lactate-buffered PDF with physiological pH (n=8), bicarbonate/lactate-buffered PDF with acidic pH (adjusted to pH 5.2 with 1 N hydrochloride, n=5), or bicarbonate/lactate buffer, without glucose, pH 7.4 (n=7). Fluids were instilled via peritoneal catheters connected to implanted subcutaneous mini vascular access ports for 8 weeks. Control animals with or without peritoneal catheters served as control groups (n=8/group). Various functional (2 h PET) and morphological/cellular parameters were analyzed. RESULTS: Compared with control groups and the buffer group, conventional lactate-buffered PDF induced a number of morphological/cellular changes, including angiogenesis and fibrosis in various peritoneal tissues (all parameters P<0.05), accompanied by increased glucose absorption and reduced ultrafiltration capacity. Daily exposure to standard or acidified bicarbonate/lactate-buffered PDF improved the performance of the peritoneal membrane, evidenced by reduced new vessel formation in omentum (P<0.02) and parietal peritoneum (P<0.008), reduced fibrosis (P<0.02) and improved ultrafiltration capacity. No significant differences were found between standard and acidified bicarbonate/lactate-buffered PDF. During PET, acidic PDF was neutralized within 15 to 20 min. CONCLUSION: The bicarbonate/lactate-buffered PDF, acidity per se did not contribute substantially to peritoneal worsening in our in vivo model for PD, which might be explained by the buffering capacity of the peritoneum

Novel Role for Mast Cells in Omental Tissue Remodeling and Cell Recruitment in Experimental Peritoneal Dialysis

Because of its dynamic structure, the omentum plays a key role in the immunity of the peritoneal cavity by orchestrating peritoneal cell recruitment. Because mast cells accumulate in the omentum upon experimental peritoneal dialysis (PD) and may produce angiogenic/profibrotic factors, it was hypothesized that mast cells mediate omental tissue remodeling during PD. Daily treatment with conventional PD fluid (PDF) for 5 wk resulted in a strong omental remodeling response, characterized by an approximately 10-fold increase in mast cell density (P &lt; 0.01), an approximately 20-fold increase in vessel density (P &lt; 0.02), an approximately 20-fold increase in the number of milky spots (P &lt; 0.01), and a four-fold increase in submesothelial matrix thickness (P &lt; 0.0003) in wild-type rats. In contrast, all PDF-induced omental changes were significantly reduced in mast cell–deficient Ws/Ws rats or in wild-type rats that were treated orally with a mast cell stabilizer cromoglycate. A time-course experiment showed mast cell accumulation immediately before the formation of blood vessels and milky spots. Functionally, PDF evoked a peritoneal cell influx, which was significantly reduced in Ws/Ws rats (P &lt; 0.04) and in wild-type rats that were treated with cromoglycate (P &lt; 0.03). Cromoglycate treatment also completely prevented PDF-induced omental adhesions to the catheter tip (P � 0.0002). Mesothelial damage, angiogenesis, and fibrosis of mesentery and parietal peritoneum as well as glucose absorption rate and ultrafiltration capacity proved to be mast cell independent. Data strongly support the hypothesis that mast cells mediate PDF-induced omental tissue remodeling and, subsequently, peritoneal cell influx and adhesion formation, providing therapeutic possibilities of modulating omental function