Tehran University Medical Journal

Background: The typical features of eccentric exercise-induced muscle damage are delayed-onset muscle soreness (DOMS) and prolonged loss of muscle strength. It has been shown that passive warmth is effective in reducing muscle injury. Due to the interaction of different systems in vivo, we used isolated perfused medial gastrocnemius skeletal muscle to study the direct effect of temperature on the eccentric contraction-induced force loss.

Methods: After femoral artery cannulation of a rat, the left medial gastrocnemius muscle was separated and then the entire lower limb was transferred into a prewarmed (35^oC) chamber. With the chamber temperature at 31, 35 and 39^oC before and during eccentric contraction. Isometric force loss was measured after 15 eccentric contractions (N=7-9).

Results: Maximum contraction force reduction has been used as an index for eccentric contraction-induced force loss. In this study eccentric contraction caused a significant reduction in maximum isometric tension (p<0.01), but no significant difference was seen in isometric force loss at 31^oC and 39^oC compared with that at 35^oC.

Conclusions: Our results suggest that temperature changes before or during eccentric contractions have no effect on eccentric contraction-induced force loss.

Background: It is generally accepted that the selective adenosine triphosphate-dependent potassium channel openers (KATP openers) have a dramatic role in the treatment of some cardiovascular disorders. The aim of this study was to investigate the effects of diazoxide, a potent ATP-related potassium channel opener, on spontaneously beating isolated rat atria to achieve more accurate approaches to treat cardiovascular diseases, such as atrial related disorders including atrial arrhythmias.
Methods: After induction of anesthesia, we exsected the heart and isolated the atria of 48 male Wistar rats. Later, we recorded the beating and contractile force of the atria by a physiograph. Subsequently, we studied the effects of diazoxide (2 to 100 µg/mL) on beating and contractile force of the isolated atria 5, 10, 15 and 20 minutes after applying the drug onto the atria.
Results: Diazoxide administration (2 to 100 µg/mL) showed a significant decrease (7% to 49% depending on concentration) in atrial beatings (P≤0.001) and in contractile force (1.5% to 67% depending on concentration), (P≤0.001). The effects began several minutes after applying the drug onto the tissues.
Conclusion: This study revealed that diazoxide has a direct concentration-dependent effect on cardiac performance and leads to reduction in beating rates and contractile force of the heart. This effect seems to be related to the activation of mitochondrial or sarcolemmal KATP channels. Since the inhibitory action of diazoxide on the heart was very remarkable and prompt, this agent may also exhibit antiarrhythmic properties.