Effects of Capillary Microsampling on Toxicological Endpoints in Juvenile Rats

Blood sampling during juvenile rat toxicology studies is required to determine the toxicokinetic (TK) profile of compounds. Juvenile rats are too small to undergo repeated blood sampling using conventional methods, which collect 200-300 μl blood at each time point. Recently, capillary microsampling (CMS) gained interest because sample sizes are almost 10 times smaller enabling multi-sample collection from 1 rat. Here, we evaluated the use of CMS in juvenile rats in support of reduced animal usage. Juvenile rats at postnatal day (PND) 4, 10, and 17 underwent CMS via the submandibular, tail, and jugular veins. The CMS methods for pups at different ages were evaluated based on sample quality and technical practicality as well as on acute and chronic changes of toxicological parameters. The best location for CMS was the submandibular vein for PND 4 and 10 pups and the tail vein for PND 17 pups. No effects were found on clinical signs, body and organ weights and biochemistry parameters when 2 × 32 μl of blood was withdrawn from PND 4 pups or when 3 × 32 μl was taken from PND 10 and 17 pups within 24 h. Significant changes in several hematology parameters were observed 24 h after CMS due to a decrease of red blood cells and renewed production. These values had recovered to normal 7 days after CMS. CMS is feasible in juvenile rats for TK assessment. Utilizing this method could decrease the number of additional animals by 75%.