Diabetes mellitus is a chronic metabolic disease, which results in serious cardiac complications. It has been shown that hemodynamic parameters are impaired in diabetic rat heart. Leptin is a hormon secreted from adipose tissue and have important effects on glucose metabolism. The effect of leptin treatment on cardiac hemodynamic parameters in streptozotocine (STZ) induced diabetic rat heart has not been studied yet. Thus, we aimed to investigate whether leptin treatment could ameliorate impaired basal cardiac hemodynamic parameters in STZ diabetic rat.

Male Sprague-Dawley rats were used for this study. The rats were divided into 3 groups; control (C), diabetic (D), leptin treated diabetic group (Lep). Diabetes was induced by single dose streptozotocin injection (40mg/kg, i.v.). At the end of 10-week-diabetes period some of the diabetic rats were treated with leptin (150μg/kg/day, via osmotic minipump) for 14 days. In vivo cardiac hemodynamic parameters were determined through pressure-volume (PV loop) relations. First pressure in carotid artery [systolic arterial pressure (SP), diastolic arterial pressure (DP), mean arterial pressure (MAP)] were measured, then PV loops were recorded under isofluoran anesthesia (%2). Cardiac hemodynamic parameters include heart rate (HR), end systolic pressure (ESP), end diastolic pressure (EDP), the rate of contraction and relaxation (dp/dtmax and dp/dtmin), end systolic volume (ESV), end diastolic volume (EDV), stroke volume (SV), cardiac output (CO), ejection fraction (EF), isovolumic relaxation constant (Tau, Weiss and glantz method), end systolic elastance (Ees), cardiac stiffness, preload recruitable stroke work (PRSW) and dp/dt-EDV relation. To assess preload recruitable cardiac parameters inferior vena cava occlusion was made.

PV loop analysis showed that almost all cardiac hemodynamic parameters were altered in diabetic state as expected. Heart rate of rats were decreased in D group, leptin treatment did not improve it significantly. ESP values were decreased in D group. Leptin treatment increased it markedly, however it did not reach control levels. EDP values did not differ between the groups. Both dp/dtmax and dp/dtmin values were significantly attenuated in D group, leptin treatment ameliorated it markedly. EDV values were enhanced in D group, and decreased after leptin treatment. There were no significant changes in SV between the groups. CO was found to be attenuated in D group. EF values were not changed. Tau values were increased markedly in D group, and improved with leptin treatment, however it was still high compared to C group. Ees was decreased in D group. No significant change was seen after leptin treatment. The stiffness of the left ventricle was increased in D group and decresed after leptin treatment. PRSW was attenuated in D group and leptin treatment improved it markedly. dp/dt-EDV relation was also decreased in D group and ameliorated partly in Lep group. SP, DP and MAP were decreased in D group and ameliorated in Lep group.

In vivo cardiac experiments showed that heart function was impaired in diabetic rats. Leptin exerted beneficial effects on these parameters, however the values did not reach control levels. This may be related to chosen dose of leptin, which has been demonstrated effective in a previous study. To confirm the dose dependency of the effect, cardiac parameters should be evaluated in rats treated with a higher dose of leptin.