Impairment on cardiovascular and autonomic adjustments to maximal isometric exercise tests in offspring of hypertensive parents.

The objective of the present study was to compare cardiovascular and autonomic responses to a mental stress test and to a maximal isometric exercise test between offspring of normotensive (ON, n = 10) and hypertensive parents (OH, n = 10). Subjects underwent a 3-min Stroop Color Word Test and a maximal isometric exercise test performed in an isokinetic dynamometer with continuous RR interval monitoring. At rest, arterial pressure and heart rate were similar between groups, but there was a significant reduction in total RR interval variance (ON: 5933 ± 493 vs. OH: 2967 ± 390 ms(2)) and an increase in low-high frequency components ratio of heart rate variability (ON: 2.3 ± 0.4 vs. OH: 4.6 ± 0.8) in OH group. In the first minute of the mental stress test and after both tests, the OH group presented increased heart rate as compared with the ON group. After both tests, only the ON group presented an increase in sympathetic component, thus reaching resting values similar to those of the OH group. Our data demonstrated increased resting cardiac sympathetic modulation in offspring of hypertensive parents at similar levels to that observed in offspring of normotensive parents after a mental stress test or a maximal isometric exercise test. Additionally, the exacerbated heart rate responses to these physiological tests in OH subjects may be associated with resting autonomic dysfunction, thus reinforcing these evaluations as important tools for detecting early dysfunctions in this genetically predisposed population.

Benefits of exercise training in diabetic rats persist after three weeks of detraining.

Regarding all benefits of exercise training, a question remains: how long are these benefits kept? This study evaluated the effect of 3-week detraining after 10 weeks of training in STZ-diabetic rats. Male Wistar rats were assigned into: sedentary controls, trained controls, trained-detrained controls, sedentary diabetic, trained diabetic and trained-detrained diabetic. Arterial pressure (AP) and heart rate (HR) were recorded by a data acquisition system. Baroreflex sensitivity (BRS) was evaluated by HR responses to AP changes induced by infusion of vasoactive drugs. Intrinsic heart rate (IHR), sympathetic tonus (ST) and vagal tonus (VT) were evaluated by pharmacological blockade with atenolol and atropine. Spectral analysis of systolic AP and HR variabilities (HRV) was performed to estimate autonomic modulation to the heart and vessels. Diabetes cardiovascular and autonomic dysfunctions were reversed by exercise training and partially maintained in the 3-week detraining period. In controls, training decreased AP and HR and improved BRS, changes that returned to baseline values after detraining. IHR and VT were improved in trained diabetic rats and remained in detrained diabetic ones. LF component of HRV decreased in trained control group. In diabetics, exercise training improved variance, and absolute LF and HF components of HRV. Only HF was maintained in detrained diabetic group. Moreover, there was an inverse relationship between plasma glucose and the absolute HF component of HRV. These changes probably determined the different survival rate of 80% in diabetic detrained and 51% in diabetic sedentary rats.

Maximal exercise test is a useful method for physical capacity and oxygen consumption determination in streptozotocin-diabetic rats.

BACKGROUND: The aim of the present study was to investigate the relationship between speed during maximum exercise test (ET) and oxygen consumption (VO2) in control and STZ-diabetic rats, in order to provide a useful method to determine exercise capacity and prescription in researches involving STZ-diabetic rats. METHODS: Male Wistar rats were divided into two groups: control (CG, n = 10) and diabetic (DG, n = 8). The animals were submitted to ET on treadmill with simultaneous gas analysis through open respirometry system. ET and VO2 were assessed 60 days after diabetes induction (STZ, 50 mg/Kg). RESULTS: VO2 maximum was reduced in STZ-diabetic rats (72.5 +/- 1 mL/Kg/min-1) compared to CG rats (81.1 +/- 1 mL/Kg/min-1). There were positive correlations between ET speed and VO2 (r = 0.87 for CG and r = 0.8 for DG), as well as between ET speed and VO2 reserve (r = 0.77 for CG and r = 0.7 for DG). Positive correlations were also obtained between measured VO2 and VO2 predicted values (r = 0.81 for CG and r = 0.75 for DG) by linear regression equations to CG (VO2 = 1.54 * ET speed + 52.34) and DG (VO2 = 1.16 * ET speed + 51.99). Moreover, we observed that 60% of ET speed corresponded to 72 and 75% of VO2 reserve for CG and DG, respectively. The maximum ET speed was also correlated with VO2 maximum for both groups (CG: r = 0.7 and DG: r = 0.7). CONCLUSION: These results suggest that: a) VO2 and VO2 reserve can be estimated using linear regression equations obtained from correlations with ET speed for each studied group; b) exercise training can be prescribed based on ET in control and diabetic-STZ rats; c) physical capacity can be determined by ET. Therefore, ET, which involves a relatively simple methodology and low cost, can be used as an indicator of cardio-respiratory capacity in future studies that investigate the physiological effect of acute or chronic exercise in control and STZ-diabetic male rats.