Implicações termorregulatórias dos receptores AT2 centrais durante o exercício físico em ratos

Abstract

Aim: The aim of the study was to verify the effect of central angiotensin ll AT2 receptor blockade in thermoregulatory responses during exercise in rats. Material and methods: Wistar rats weighing between 250 and 350g. Were implanted with a guide cannula in the right lateral cerebral ventricle for administration of 2µL PD (10 μg, n = 7) or 0,15 M NaCl (SAL, n = 7). The internal body temperature (Tb) was determined by telemetry via a temperature sensor implanted in the animal's intraperitoneal cavity. The tail temperature (Ttail) was measured using a temperature sensor attached to the animal's tail. Both temperatures were measured continuously, during resting and while the animals performed submaximal exercise at a speed of 18m/min and 5% inclination, until failure. From the data obtained, body heating rate (BHR), heat storage rate (HSR), body temperature threshold for tail vasodilation (TTbV), time to fatigue (TTF) and workload (W) were determined. Results: Tb remained stable in both group, and no difference was seen between treatments during a resting period. It was observed that icv administration of PD promoted an increase of 17% in the TTF (18 ± 1,8 min, PD vs. 15 ± 2,1 min, SAL, p < 0,01), and of 20% in the W, when compared with controls (4,62 ± 0,34 kgm, PD vs. 3,74 ± 0,4 kgm, SAL, p < 0,01). Despite that the rats injected with PD exhibited similar increase in Tb during exercise, at fatigue point it was found greater variation of Tb (2,37 ± 0,24 °C, PD; 1,73 ± 0,21 °C, SAL, p< 0,05). However, no difference was seen between BHR (0,14 ± 0,01 °C.min-1, PD vs. 0,13 ± 0,02 °C.min-1, SAL), HSR (33,75 ± 1,37 cal. min-1, PD vs. 30,9 ± 2,82 cal. min-1, SAL) and TTbV (37,75 ± 0,12 °C, PD vs. 37,61 ± 0,15 °C, SAL) in both group. Additionally, from the 13° minute of exercise until fatigue, Ttail variation was higher in PD animals (4,87 ± 0,44 °C, PD; 3,10 ± 0,57 °C, SAL, p<0,05), and closely related with the increased TTF (r= 0,871, p <0,01). Conclusion: The data shows that AT2 receptor blockade improves heat balance during exercise due to better ability to dissipate heat, which contributed to superior exercise performance.