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. 2006 Dec 4:5:26.
doi: 10.1186/1475-2840-5-26.

Myocardial performance in conscious streptozotocin diabetic rats

Giulianna R Borges  1 , Mauro de Oliveira, Helio C Salgado, Rubens Fazan Jr
Affiliations

Myocardial performance in conscious streptozotocin diabetic rats

Giulianna R Borges et al. Cardiovasc Diabetol. .

Abstract

Background: In spite of a large amount of studies in anesthetized animals, isolated hearts, and in vitro cardiomyocytes, to our knowledge, myocardial function was never studied in conscious diabetic rats. Myocardial performance and the response to stress caused by dobutamine were examined in conscious rats, fifteen days after the onset of diabetes caused by streptozotocin (STZ). The protective effect of insulin was also investigated in STZ-diabetic rats.

Methods: Cardiac contractility and relaxation were evaluated by means of maximum positive (+dP/dtmax) and negative (-dP/dtmax) values of first derivative of left ventricular pressure over time. In addition, it was examined the myocardial response to stress caused by two dosages (1 and 15 mug/kg) of dobutamine. One-way analysis of variance (ANOVA) was used to compare differences among groups, and two-way ANOVA for repeated measure, followed by Tukey post hoc test, to compare the responses to dobutamine. Differences were considered significant if P < 0.05.

Results: Basal mean arterial pressure, heart rate, +dP/dtmax and -dP/dtmax were found decreased in STZ-diabetic rats, but unaltered in control rats treated with vehicle and STZ-diabetic rats treated with insulin. Therefore, insulin prevented the hemodynamic and myocardial function alterations observed in STZ-diabetic rats. Lower dosage of dobutamine increased heart rate, +dP/dtmax and -dP/dtmax only in STZ-diabetic rats, while the higher dosage promoted greater, but similar, responses in the three groups. In conclusion, the results indicate that myocardial function was remarkably attenuated in conscious STZ-diabetic rats. In addition, the lower dosage of dobutamine uncovered a greater responsiveness of the myocardium of STZ-diabetic rats. Insulin preserved myocardial function and the integrity of the response to dobutamine of STZ-diabetic rats.

Conclusion: The present study provides new data from conscious rats showing that the cardiomyopathy of this pathophysiological condition was expressed by low indices of contractility and relaxation. In addition, it was also demonstrated that these pathophysiological features were prevented by the treatment with insulin.

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Figures

Figure 1
Figure 1
Responses of +dP/dtmax and -dP/dtmax to β1-adrenergic stimulation with dobutamine (1 and 15 μg/kg) in conscious control (treated with vehicle) rats, and conscious diabetic rats obtained by means of streptozotocin (STZ), treated (STZ+Insulin), or not (STZ-diabetic), with insulin. Data are reported as means ± SEM. *P < 0.05 compared to the other groups stimulated with 1 μg/kg; +P < 0.05 compared to their counterparts stimulated with 1 μg/kg.
Figure 2
Figure 2
Responses of heart rate and mean arterial pressure to β1-adrenergic stimulation with dobutamine (1 and 15 μg/kg) in conscious control (treated with vehicle) rats, and conscious diabetic rats obtained by means of streptozotocin (STZ), treated (STZ+Insulin), or not (STZ-diabetic), with insulin. Data are reported as means ± SEM. *P < 0.05 compared to the other groups stimulated with 1 μg/kg; +P < 0.05 compared to their counterparts stimulated with 1 μg/kg.
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