Ain 76

Chronic hyponatremia was induced in vivo within 3.5 days using a vasopressin-filled mini-osmotic ALZET pump (Model 2002, Durect Corp., Cupertino, USA) and a rodent liquid diet (AIN-76, Bio-Serv, NJ, USA), according to Verbalis [34 ]. First, the rats were acclimated for 2 days to a rodent liquid diet administered in the amount of 75 ml and supplying 1.0 kcal/mL. During this time, they had free access to drinking water. Osmotic pumps filled with vasopressin were implanted subcutaneously on the neck under chloral hydrate anesthesia. The pump released vasopressin at a rate of 2.4 μg/24 h. Starting from the first day following implantation of the pump, the animals were fed the liquid diet AIN-76 containing 14% glucose in the amount of 50 mL/24 h. At this time, drinking water was withheld to prevent excessive water intake with escape from antidiuresis [35 (link)]. After 3.5 days of AVP infusion, the animals were decapitated under 5% isoflurane in 70% NO₂/30% O₂ anesthesia and the middle cerebral arteries were isolated as described below and blood samples were collected to measure the osmolality and concentration of Na⁺ in plasma.
Control rats were housed individually for the duration of the experiment with free access to drinking water and standard rat chow.

Mice assigned to the Day seven sacrifice were placed into metabolism cages following SPIO nanoparticle exposure for urine and feces collection. They remained in the metabolism cages for the duration of the study. Feces and urine were collected daily, weighed, and stored frozen at ~-70°C for subsequent analysis. While in the metabolism cages, mice were provided with a certified liquid diet (BIOSERV, AIN-76) rather than pelleted rodent chow to prevent excessive contamination of samples from pelleted feed. Fresh liquid diet was given daily. These mice were acclimated to the liquid diet for ~ three days prior to their placement into the metabolism cages. Testing conducted prior to study indicated that mice readily consumed the liquid diet and maintained a normal weight while on the diet.