Endocrine Abstracts

Background: Elevated serum retinol binding protein 4 (RBP4) levels were previously described in insulin-resistance states. Recently it was shown that RBP4 contributes, at least partly, to the pathogenesis of insulin resistance in spontaneously hypertensive rats (SHR), but the effects of exercise training and time-course of changes after detraining on RBP4 levels have not yet been explored.

Aims: To examine the effects of exercise training and short-term detraining on serum RBP4 levels and insulin resistance in SHR.

Methods: Thirty-two male SHR, 4 months old, were submitted to 10-week treadmill training, 5 times/week (T) or kept sedentary for the same period (S). Two short periods of exercise detraining were also carried out (2 and 4 days: D2 and D4). Body weight, insulin sensitivity (insulin tolerance test, ITT), functional capacity (maximal exercise test) and serum RBP4 (ELISA) were measured. Repeated ANOVA and Pearson’s correlation were used (P<0.05).

Results: Rats had the same characteristics at baseline. There was a ~43% gain in body weight over time (P=0.004) in all groups. However, in exercise-trained rats there was a ~40% (P<0.001) reduction of white fat tissue weight (epididymal) as compared to the S group. Exercise training determined an improvement of insulin sensitivity (S: 3.8±1.0, T: 4.4±1.0, D2: 5.9±1.2, D4: 4.1±1.7% per min, P=0.001) and increased function capacity (S: 1.4±0.3, T: 2.4±0.3, D2: 2.6±0.1, D4: 2.7±02 km/h, P<0.001), which was not lost after detraining. RBP4 levels were reduced in response to exercise training (~45%, P=0.015). There was a negative correlation between insulin resistance and serum RBP4 (r=-0.690, P<0.001). The short periods of detraining were not enough to change any 10-week training-induced benefits.

Figure 1 Serum retinol binding protein 4 (RBP4) in response to exercise training and detraining. S, sedentary; T, 10-week trained; D2, 2 days detrained; D4, 4 days detrained. Initial: pre-training measures. Final: measures after exercise training period or after the respective periods of detraining. Repeated measures ANOVA: P (group)<0.001, P (time)<0.001 and P (interaction)=0.015, followed by post hoc Bonferroni: ^*P<0.05 vs S in the final period. Significances over time are also presented.

Conclusions: Exercise training determined a decrease in serum RBP4, accompanying the improvement in insulin sensitivity. These benefits were maintained for 4 days of exercise detraining. The inverse association between RBP4 levels and insulin resistance could represent a causal relationship between them.

Financial support: CNPq and Fapergs.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This work was supported, however funding details unavailable.