Franny Jongbloed

26 CHAPTER 2 RESULTS Fasted aged-overweight mice show a gradual weight gain after renal IRI Male and femaleF1-FVB/C57BL6-hybridmicewere either fasted for threedays bypermitting water only or fed ad libitum (AL) preceding surgery. The mean baseline weight was 47.4±5.1 and 48.0±7.6 grams for male and female mice, respectively, demonstrating their overweight phenotype acquired by ad libitum conditions compared to their mean body weight at 12 weeks: 31.4±3.1 (male) and 24.2 ±2.4 (female) (data not shown). Fasting resulted in a net body weight loss of 8.2±0.5 and 6.5±0.9 grams inmales and females, respectively, correlating with approximately 17% and 14% of their body weight before fasting (Figure 1A). After IRI, the fasted male and female mice showed a 5% and 10% weight loss, respectively, in the first five postoperative days (POD), after which their weight stabilized (Figure 1A). From POD7 on, they gradually gained weight and eventually reached their preoperative weight (t=0) at day 28. In contrast, the AL fed mice showed a larger and faster weight loss after IRI. The AL fed males lost 7% in three days, after which they had all died. The AL fed females lost slightly more relative weight during the same period (10%). By POD5, they had lost 21% of their weight, resulting in a total weight slightly below that reached by the fasted animals. After POD7, the single surviving AL fed female mouse showed a similar trend in body weight gain as the fasted mice. Three-day fasting confers resistance to renal ischemia in aged-overweight mice At surgery, bilateral renal ischemia was applied for 37 minutes in male and 60 minutes in female mice followed by reperfusion. Both male and female fasted mice had a significant improved survival compared to the AL fed groups (Figure 1B). All eight AL male mice died or were sacrificed because of morbidity indicative of kidney failure within three days following reperfusion, whereas 7/8 fasted males survived through POD7. At POD7, four male mice were sacrificed for pathological analysis and censored in Figure 1B. Two of the three remaining mice survived in good health through day 28. In the fasted female group, one mouse was found dead on POD1 after IRI because of secondary causes (sutures removed by animal) and was excluded from further analyses. One of the 11 ad libitum fed females survived the observation period, while the majority, nine in total, died or were sacrificed due to morbidity within three days following IRI. At 28 days, 7/10 fasted female mice were still alive and appeared healthy. All fasted mice that died showed indications of irreversible kidney failure (morbidity and loss of kidney function, see serum and histology data described further on).