Effects of concentration and time on the carageenaninduced inflammation in rats

Carageenan is used to induce experimental inflammation in laboratory animals to study the pathophysiology and treatment of inflammatory conditions. Despite its routine use in research, different protocols have been suggested to administer carageenan in the laboratory animals. This work aimed at finding the most appropriate dosage regimen for carageenan to induce inflammation in the rat musculoskeletal system. In this study, 32 limbs of 8 male Wistar rats were injected subcutaneously at the palmar side of either hand or foot with 0.1 mL of either of the following concentrations of carageenan: 0, 1. 2, or 4 mg/mL. Thickness of the limb was measured by a micrometer apparatus before as well as 0.5, 2, 6 and 24 hours after the injection. The highest level of inflammation occurred 2 h after the injection of all concentrations. Six h after the injection, there was no difference between the control and treated groups. At 120 min after injection of 1, 2 and 4 mg/mL of carageeninan, the increased width of the limb was 18%, 18% and 21%, respectively. The inflammation reached the level of significance only 30 min after injection of the lowest concentration used, i.e. 1 mg/mL (P < 0.05). The use of carageenan for induction and investigation of inflammatory responses may be useful solely in early acute inflammation (30 min post-injection) at lower concentrations (1 mg/mL). Based on our observations, carageenan should not be considered as a right choice for this sort of research work.