FIGURE 4. Cold intolerance of iPLA₂γ KO mice.

For cold tolerance tests, mice (4 – 6 months) were individually housed at 4°C in standard breeding cages containing bedding with free access to food and water. Rectal core body temperatures were measured using a thermocouple probe inserted 2 cm into the rectum until a stable reading was obtained. Measurements were taken every 60 min for up to 24 h or until the mice became torpid or the core temperature dropped below ~28°C, after which mice were removed for recovery. All WT mice maintained their body temperature between 30 and 36°C during the entire course of the studies (24 h). The bar graph shows mean cold tolerance time ± S.E. for male and female WT (solid bars) and KO (open bars) animals. The mean time at which male KO mice were able to maintain their core body temperature was 15.3 ± 2.7 h (n = 6 per group, p < 0.05 by Student’s t test) compared with WT controls (which maintained their body temperatures for the entire experimental interval). For female KOs, the corresponding mean endurance time at 4°C was 11.5 ± 3.4 h (n = 6 per group, p < 0.02) compared with WT controls, which maintained their body temperatures throughout the entire experimental interval.