Exercise at anaerobic threshold intensity and insulin secretion by isolated pancreatic islets of rats

Abstract

To evaluate the effect of acute exercise and exercise training at the anaerobic threshold (AT) intensity on aerobic conditioning and insulin secretion by pancreatic islets, adult male Wistar rats were submitted to the lactate minimum test (LMT) for AT determination. Half of the animals were submitted to swimming exercise training (trained), 1 h/day, 5 days/week during 8 weeks, with an overload equivalent to the AT. The other half was kept sedentary (sedentary). At the end of the experimental period, the rats were submitted to an oral glucose tolerance test and to another LMT. Then, the animals were sacrificed at rest or immediately after 20 minutes of swimming exercise at the AT intensity for pancreatic islets isolation. At the end of the experiment mean workload (% bw) at AT was higher and blood lactate concentration (mmol/L) was lower in the trained than in the control group. Rats trained at the AT intensity showed no alteration in the areas under blood glucose and insulin during OGTT test. Islet insulin content of trained rats was higher than in the sedentary rats while islet glucose uptake did not differ among the groups. The static insulin secretion in response to the high glucose concentration (16.7 mM) of the sedentary group at rest was lower than the sedentary group submitted to the acute exercise and the inverse was observed in relation to the trained groups. Physical training at the AT intensity improved the aerobic condition and altered insulin secretory pattern by pancreatic islets.

Figure 1

Determination of the Anaerobic Threshold (AT) of a single rat of the control group during lactate minimum test at the beginning of the experiment. Each point indicates blood lactate concentration (mmol/L) on the ordinate after 5 min exercise bout with the animal supporting each load indicated on the abscissa. The blood lactate concentration (6.81 mmol/L) and the respective workload (5.02% b.w.) were calculated using the degree 2 polynomial function (y = 1.2214x² − 12.267x + 37.607) that defined the curve. This minimum value of blood lactate concentration indicated the workload equivalent to AT.

Figure 2

Mean values of workload (% of body weight) equivalent to the anaerobic threshold (AT) determined by the lactate minimum test for the rats assigned to sedentary and trained groups at the beginning and the end of the experimental period. *Significantly different (p < 0.05, ANOVA two-way) in relation to equivalent sedentary group.

Figure 3

Mean values blood lactate concentration (mmol/L) equivalent to the anaerobic threshold (AT) determined by the lactate minimum test for the rats assigned to sedentary and trained groups at the beginning and the end of the experimental period. *significantly different (p < 0.05, ANOVA two-way) in relation to equivalent sedentary group.

Figure 4

Insulin concentration in pancreatic isolated islets of the animals at the end of 8 weeks of the experimental period. Results are mean ± standard deviation of 6 experiments. *Significantly different (p < 0.05, ANOVA two-way) in relation to equivalent sedentary group.

Figure 5

Glucose uptake by pancreatic isolated islets in response to different glucose concentrations at the end of the experimental period. Results are mean ± standard deviation of 8 experiments. *Significantly different (p < 0.05, ANOVA two-way) from glucose concentration at 2.8 mM.

Figure 6

Glucose oxidation by pancreatic isolated islets in response to different glucose concentrations at the end of the experimental period. Results are mean ± standard deviation of 8 experiments. *Significantly different (p < 0.05, ANOVA two-way) from glucose concentration of 2.8 mM.

Figure 7

static insulin secretion by pancreatic isolated islets in response to different glucose concentrations at the end of the experimental period. Results are mean ± standard deviation of 8 experiments. *Significantly different (p < 0.05, ANOVA two-way) from glucose concentration at 2.8 mM; ● significantly different (p < 0.05, ANOVA two-way) from sedentary group at rest (Sed Rest); # significantly different (p < 0.05, ANOVA two-way) from trained group at rest (Trained Rest).