Analysis of Animal Well-Being When Supplementing Drinking Water with Tramadol or Metamizole during Chronic Pancreatitis

Abstract

Pain management during in vivo experiments is an animal welfare concern and is in many countries also legally required. In this study, we evaluated C57Bl/6J mice when 3 g/L metamizole or 1 g/L tramadol was provided via drinking water, before and during cerulein-induced chronic pancreatitis. Supplementation of drinking water with metamizole or tramadol did not significantly reduce the amount of consumed water. In order to evaluate the wellbeing of mice, a distress score, burrowing activity, nesting behavior, and body weight was assessed. Before induction of pancreatitis, neither tramadol nor metamizole influenced these readout parameters. Chronic pancreatitis caused a significantly increased distress score, decreased burrowing activity and a reduction in body weight. Mice drinking tramadol-supplemented water experienced less loss in body weight and consumed more water than mice drinking metamizole, at a few time-points during chronic pancreatitis. Pancreatic atrophy, a characteristic feature of chronic pancreatitis was not differentially influenced by either analgesic. In conclusion, both analgesics can be used during 33 days of chronic pancreatitis, but tramadol seems to be moderately advantageous when compared to metamizole.

Keywords: analgesia; rodents; sweetened water; wellbeing.

Figure 1

Experimental procedure for evaluating analgesics. C57Bl/6J mice were allocated (a) to a metamizole or a tramadol group on day −25 and these analgesics were added to the drinking water as indicated. The water was supplemented with sucrose on day −14 to day −10. Chronic pancreatitis was induced by three repetitive cerulein injections (c) at the indicated days, and the mice were euthanized (e) on day 33 in order to analyze the pancreas. A distress score (ds), burrowing (b), as well as nesting (n) activity and the body weight (bw) was evaluated during the indicated phases of the experiment. metamizole: n = 7; tramadol: n = 7.

Figure 2

Impact of analgesics on burrowing as well as nesting activity and body weight during the pre-experimental phase. Burrowing activity (A), nesting activity (B), and percentage of body weight compared to day −26 (C) was assessed, using drinking water without or with sucrose. No statistically significant differences between metamizole and tramadol treatment were obtained (using two-way repeated measure ANOVA with Sidak’s correction for multiple comparisons). Metamizole: n = 7; tramadol: n = 7.

Figure 3

Impact of analgesics on water consumption during the pre-experimental phase. Water Consumption (mL) divided by body weight (g) was assessed on the days indicated, using drinking water, without (A) or with sucrose (B). * Statistically significant differences between metamizole and tramadol treatment was obtained (using two-way repeated measure ANOVA in a mixed-effect model with Sidak’s correction for multiple comparisons). Metamizole: n = 6–7 (since the water bottle for one animal leaked on day −21, day −20, day −19, and day −12, these data were not included); tramadol: n = 7.

Figure 4

Pancreas weight to body weight ratio without and after chronic pancreatitis. The pancreas weight to body weight ratio of healthy mice (Con, black triangles) was significantly higher than the ratio observed in mice, which suffered from chronic pancreatitis and drank metamizole (Met, blue circles) or tramadol (Tra, red squares). No significant difference between the metamizole- and tramadol-treated animals was observed. * p ≤ 0.05 (one-way ANOVA with Sidak’s correction for multiple comparisons). Healthy mice: n = 12, metamizole: n = 7; tramadol: n = 7.

Figure 5

Impact of analgesics on readout parameters for animal distress during chronic pancreatitis. A distress score (A), the percentage burrowing activity compared to day −5 (B), nesting activity (C), fecal corticosterone metabolites concentration (D) and the percentage of body weight compared to day −5 (E) was assessed before (day −4) and during the early (day 2), middle (day 16), and late phase (day 30) of chronic pancreatitis. ^# p ≤ 0.05 between indicated days (two-way repeated measure ANOVA with Tukey correction for multiple comparison). * p ≤ 0.05 between the metamizole and the tramadol groups were obtained (two-way repeated measure ANOVA with Sidak’s correction for multiple comparisons). Metamizole: n = 7; tramadol: n = 7.

Figure 6

Impact of analgesics on water consumption during chronic pancreatitis. Water consumption (mL) divided by body weight (g) was assessed before (day −4) and during the early (day 2), middle (day 16), and late phase (day 30) of chronic pancreatitis. * p ≤ 0.05 between the metamizole and tramadol group was obtained (two-way repeated measure ANOVA with Sidak’s correction for multiple comparisons). Metamizole: n = 7; tramadol: n = 7.