Streptozotocin-induced diabetes disrupts the body temperature daily rhythm in rats

Abstract

Background: In mammals, the temperature rhythm is regulated by the circadian pacemaker located in the suprachiasmatic nuclei, and is considered a "marker rhythm". Melatonin, the pineal gland hormone, is a major regulator of the endogenous rhythms including body temperature. Its production is influenced by many factors, such as type 1 diabetes mellitus. In rats, diabetes leads to hypothermia and reduced melatonin synthesis; insulin treatment reestablishes both.

Aim: To study the body temperature daily rhythm of diabetic animals and the effects of insulin and/or melatonin treatment on its structure.

Methods: We studied the effects of streptozotocin-induced diabetes (60 mg/kg) on the body temperature rhythm of Wistar rats and the possible modifications resulting from early and late treatments with insulin (6U/day) and/or melatonin (daily 0.5 mg/kg). We monitored the daily body temperature rhythm, its rhythmic parameters (MESOR, amplitude and acrophase), glycemia and body weight for 55 days. Data were classified by groups and expressed as mean ± SEM. One-way ANOVA analysis was performed followed by Bonferroni posttest. Statistical significance was set at p < 0.05.

Results: Diabetes led to complete disruption of the temperature rhythm and hypothermia, which were accentuated over time. All early treatments (insulin or/and melatonin) prevented the temperature rhythm disruption and hypothermia. Insulin plus melatonin restored the body temperature rhythm whereas insulin alone resulted less efficient; melatonin alone did not restore any of the parameters studied; however, when supplemented close to diabetes onset, it maintained the temperature rhythmicity. All these corrective effects of the early treatments were dependent on the continuous maintenance of the treatment.

Conclusions: Taken together, our findings show the disruption of the body temperature daily rhythm, a new consequence of insulin-dependent diabetes, as well as the beneficial effect of the complementary action of melatonin and insulin restoring the normal rhythmicity.

Keywords: Daily rhythms; Insulin; Melatonin; Type 1 diabetes mellitus.

Figure 1

Experimental design. Young male rats were entrained to a 12:12 LD photoperiodic cycle for two weeks. Then, they were surgically implanted with E-mitter probes and their body temperature rhythm was recorded for 1 week every 30 seconds. After that, they were diabetic induced with streptozotocin and separated in two large groups: A) late treated and B) early treated with insulin (INS), melatonin (MEL) or a combination of both (INS + MEL). The first group started their treatment 33 days after STZ injection for fifteen days; the second group (B) begun the treatments three days after STZ, for fifteen days. After that, the treatments were interrupted and their rhythms recorded for other fifteen days. At day 41, treatments were resumed for fifteen more days.

Figure 2

Daily rhythm of body temperature in diabetic animals. Representative double-plot thermograms of BT in late-treated animals (top row) and early-treated animals (bottom row) with insulin (A, D), melatonin (B, E) or a combination of both hormones (C, F). Red to yellow coloration indicates higher temperatures and black to grey coloration indicates lower temperatures throughout 55 days of record in 30 seconds bins. Black and white rectangles under the thermograms indicate the LD cycle maintained during the experiments. Late treated animals, (A-C): control period (lateral top white bar), long-term diabetic period (lateral black bar), and treated period (bottom white bar). Early treated animals (D-F):short-term diabetic period (lateral top black bar), early treatment (top white bar), off-treatment period (bottom black bar) and restituting treatment period (bottom white bar). The white arrow indicates the moment of the STZ injection.

Figure 3

Cosine adjusted curve of late-treated and early-treated diabetic animals. Diabetic animals received late treatment (left column) or early treatment (right column) with insulin (A, D), melatonin (B, E) or a combination of both hormones (C, F). The cosine adjusted curve was obtained with Cosinor analyses for each day of the recording of each animal. The resulting data for each day (24 bins) was plotted throughout the recording (55 days). Only days that showed a 24 h oscillation in the Cosinor analysis were used. Lines indicate the moments of the STZ injection, the treatments and their interruption.

Figure 4

Acrophase map of late-treated and early-treated diabetic rats. Diabetic animals received late treatments (top row) or early treatments (bottom row) with insulin (A, D), melatonin (B, E) or a combination of both hormones (C, F). To generate the map, acrophases resulting from day-to-day analyses (averaged in 1 day bins) that showed 24 h oscillations were plotted according to the indicated ZT to generate the daily pattern vertically (mean ± SEM). Arrows indicate the days of STZ induction, treatments and their interruption.

Figure 5

Histogram of mean BT for Late-INS, Late-MEL and Late-INS + MEL treated diabetic animals. ONE-way ANOVA with p < 0.0001 for treatment factor followed by Bonferroni post-test. ***p < 0.001 vs CT, ^### p < 0.001 vs D. Mean ± SEM.

Figure 6

Histogram of mean BT for Early-INS, Early-MEL and Early-INS + MEL treated diabetic animals. ONE-Way ANOVA with p < 0,0001 for treatment factor followed by Bonferroni post-test. ***p < 0.001 vs all groups, ^### p < 0,001 vs all groups..***p < 0.001 vs CT, D1 and D2. **p < 0.01 vs all groups, ^### p < 0,001 vs CT, DIM1 and D2, ^aaa p < 0,001 vs D. Mean ± SEM.