Abstract

Background: The present study was undertaken to demonstrate the anti-diabetic mode of action of Humulus lupulus L. extract and its protective influence against changes in the respiratory capacity and coronary flow of the heart in experimental diabetes.
Methods: The study was performed in non-diabetic and streptozotocin-diabetic rats. The rats were administered the plant extract at the dose of 5 mg/kg b.w. in drinking water, once daily for a maximum of 20 weeks, while another group received pure drinking water as a vehicle. Twenty animals from each group were randomly selected after the period of 1, 2.5 and 5 months, and the effects of plant polyphenolrich extract on: body weight, blood glucose level, HbA_1c level, heart mitochondria respiratory activity and coronary flow were evaluated. The heart mitochondria respiratory activity and coronary blood flow were monitored using high-resolution respirometry and the retrograde perfusion Langendorff system.
Results: There was a statistically significant decrease in body weight and increase in the level of glucose and glycated hemoglobin in diabetic subjects compared to non-diabetic ones. The plant extract did not affect any of the measured parameters in the diabetic animals compared to those not treated with the extract. The majority of the heart mitochondria parameters remained at a similar level to those recorded in the cardiomyocytes isolated from healthy rats. Multiple parameters of coronary flow were also not affected by the extract supplementation. The NO-independent coronary vessel blood flow was significantly improved only after the 5^th month treatment.
Conclusion: Regardless of well evidenced development of diabetes, both the heart mitochondrial function and coronary flow in rats with STZ-induced diabetes were not significantly affected. Consequently, it was not possible to prove the scientific hypothesis that the extract of spent hops improves heart mitochondrial bioenergetics-impaired by the excessive glucose.