Recovery of Osmolarity in the Extracellular Fluid and the Brain during an Acute Hypo-osmotic Challenge

Our bodies are constantly trying to maintain homeostasis through mechanisms that can detect perturbations to this state of balance. Osmoregulation is used to maintain osmolarity and affects cell volume in which case will either increase or decrease depending on conditions of the environment they are subjected to. The purpose of the research was to better understand how an acute hypo-osmotic challenge changes the osmolarity in extracellular fluid and compare this to changes in the brain. Mice of various ages were injected with de-ionized water (10% and 20% of their bodyweight, respectively) and sacrificed at different time points after the injection. Osmolarity readings were taken from blood and brain samples at the selected times. We examined how the osmolarity recovered over time. Results indicate that there is ~19% drop in osmolarity after 30 min in the extracellular fluid and ~7% in the brain in response to 20% body weight water injection. After 48 hours, osmolarity in both extracellular fluid and brain returned to ~99% of the normal osmolarity. This manifests tighter osmoregulation in the brain than in that of the rest of the body and that the brain may have unique mechanisms to reduce hypo-osmotic stress.