Coronary hemodynamics in diabetic spontaneously hypertensive rats

Aerobic training increases renal antioxidant defence and reduces angiotensin II levels, mitigating the high mortality in SHR-STZ model

OBJECTVE

The purpose of the research was to investigate the effects of aerobic training on renal function, oxidative stress, intrarenal renin-angiotensin system, and mortality of hypertensive and diabetic (SHR-STZ) rats.

MATERIALS AND METHODS

Blood pressure, creatinine, urea levels, urinary glucose, urine volume, and protein excretion were reduced in trained SHR-STZ rats.

RESULTS

Aerobic training not only attenuated oxidative stress but also elevated the activity of antioxidant enzymes in the kid'ney of SHR-STZ rats. Training increased intrarenal levels of angiotensin-converting enzymes (ACE and ACE2) as well as the neprilysin (NEP) activity, along with decreased intrarenal angiotensin II (Ang II) levels. Aerobic training significantly improved the survival of STZ-SHR rats.

CONCLUSION

The protective role of aerobic training was associated with improvements in the renal antioxidative capacity, reduced urinary protein excretion along with reduced intrarenal Ang II and increased NEP activity. These findings might reflect a better survival under the combined pathological conditions, hypertension, and diabetes.

Myocardial blood flow and glucose metabolism in diabetes mellitus

Recent studies at our institution using positron emission tomography (PET) provide evidence that both myocardial blood flow (MBF) and glucose metabolism may be affected in patients with diabetes mellitus. A retrospective study revealed inadequate myocardial glucose uptake as assessed by 2-[18F]fluoro-2-deoxyglucose (18FDG) in 64% of type I (insulin-dependent diabetes mellitus, IDDM) and 36% of type II (non-insulin-dependent diabetes mellitus, NIDDM) patients. However, a study in 7 patients with IDDM and 9 controls showed that metabolic standardization using hyperinsulinemic-euglycemic clamp is associated with similar myocardial glucose uptake in both groups (0.43 +/- 0.16 vs 0.44 +/- 0.12 micromol/g per min; p = nonsignificant). Furthermore, we studied MBF as assessed by [13N]ammonia in 15 IDDM patients without coronary artery disease. We found an impairment in flow reserve in diabetic patients as compared with a control group of 13 healthy volunteers (2.6 +/- 1.3 vs 4.0 +/- 0.6; p <0.01), which was primarily due to a significantly higher resting MBF (95.3 +/- 27.7 vs 69.1 +/- 8.1 mL/100 g per min; p <0.01). Hyperemic flow during adenosine infusion tended to be lower in diabetics, but was not significantly different (236.3 +/- 105.7 vs 273.0 +/- 26.0 mL/100 g per min; p = nonsignificant). Morphologic and functional abnormalities of the coronary microcirculation have been reported in diabetic animals and humans. Furthermore, there is an ongoing controversy regarding the existence of a specific diabetic cardiomyopathy that is not related to epicardial coronary disease. However, few studies have explored the effect of diabetes, hyperinsulinemia, or hyperglycemia on MBF and glucose metabolism in humans. With PET it is possible to perform comprehensive noninvasive studies of various aspects of cardiac function in patients with diabetes mellitus.

Coronary microcirculation evaluation with transesophageal echocardiography Doppler in type II diabetics

Evaluation of coronary microvascular function can be obtained through coronary flow reserve measurements. The aim of this study was to evaluate the coronary microvascular function by using transesophageal-Doppler echocardiographic assessment of coronary flow reserve. The study included 32 normotensive patients with type II diabetes mellitus (group A) of short duration (6.1+/-3.8 years) aged 55.4+/-9.4 years and 14 healthy volunteers matched for age, gender and BMI (group B). No patients had clinical evidence of coronary artery disease and all of them produced a negative recent stress ECG test. Excluded from the study were patients with anemia, left ventricular hypertrophy, arrhythmia, congenital, or acquired structural heart disease. All subjects underwent transesophageal-Doppler echocardiography. Satisfactory coronary blood flow velocity recordings could be obtained from the initial segment of the left anterior descending coronary artery in healthy volunteers and in 27 patients at baseline and 2 min after dipyridamole infusion (0.56 mg/kg, for 4 min). In the remaining 5 patients no satisfactory recordings were available. The indexes of coronary flow reserve, i.e. the ratios of dipyridamole over basal maximum and mean diastolic velocities were calculated. Dipyridamole/rest maximal coronary reserve (Table 3) was 1.946+/-0.743, while this ratio for the mean diastolic velocity was 1.969+/-0.805 in group A. The respective values for group B, were 2.811+/-0.345 (P=0.000 vs. group A) and 2.914+/-0.303 (P=0.000 vs. group A). Thus, the increase in coronary flow reserve although present in both groups, it was more impressive in the normal group. Multiple regression logistic analysis of: age, sex, smoking, glucosylated hemoglobin, duration of diabetes and type of therapy, did not show any correlation of these parameters with the above ratios. This study shows that coronary flow reserve, as measured with transesophageal echocardiography-Doppler, is severely impaired in normotensive patients with type II diabetes, with relatively short duration of the disease.