CONTRACTILE FUNCTIONS OF SLOW AND FAST SKELETAL MUSCLES IN STREPTOZOTOCIN INDUCED TYPE 1 DIABETIC SPRAGUE DAWLEY RATS

Contractile Functions of Streptozotocin

Abstract

Objective: To evaluate the contractile functions of slow and fast skeletal muscles in streptozotocin induced type 1 diabetic male Sprague Dawley rats.
Study Design: Randomized control trial.
Place and Duration: Department of Physiology, Army Medical College, Rawalpindi, from April 2010 to April 2011.
Material and Methods: Thirty healthy male Sprague Dawley rats were divided into two groups. The rats in group I (male control; n = 15) were fed on normal pellet diet and water ad libitum and received single intraperitoneal injection of normal saline at the start of study (day 1). The rats in group II (male diabetic; n = 15) were fed on normal pellet diet and water ad libitum and rendered diabetic by single intraperitoneal injection of streptozotocin (STZ) 65 mg/kg body weight at the start of study (day 1). Development of diabetes was confirmed within 72 hours by measuring blood glucose levels by glucometer. At the end of four weeks, i.e on day 29, dissection of slow soleus and fast extensor digitorum longus (EDL) muscles was carried out. These muscles were selected because they represent two distinctly different fiber type populations, that is, soleus (80% type I, 20% type IIA, 0% type IIB) and EDL (0% type I, 11% type IIA, 89% type IIB). Their contractile parameters were recorded by iWorx advanced animal/human physiology data acquisition unit (AHK/214), including maximum isometric twitch tension, time to peak twitch tension, time taken to relax to 50% of the peak twitch tension, maximum fused tetanic tension, maximum fused tetanic tension after the fatigue protocol and tetanic tension after 5 minutes of rest period following the fatigue protocol.
Results: After four weeks, no significant difference was found when maximum isometric twitch tension (ITT) in isolated soleus and EDL muscles of the male diabetic group was compared with the control group. Time to peak twitch tension (TPT) and time taken to relax to 50% of the peak twitch tension (HRT) in isolated soleus muscle of the male diabetic group were significantly longer (p<0.001) as compared to the control group. On the contrary, TPT and HRT in isolated EDL muscle of the diabetic group were similar to the control group. Maximum fused tetanic tension in isolated soleus muscle of the diabetic group was similar to the control group. On the contrary, maximum fused tetanic tension in isolated EDL muscle of the male diabetic group was significantly lower (p<0.001) as compared to the control group. Maximum fused tetanic tension after the fatigue protocol and tetanic tension after 5 minutes of rest period following the fatigue protocol in isolated soleus and EDL muscles of the male diabetic group were significantly lower (p<0.001) as compared to the control group.
Conclusion: Streptozotocin induced type 1 diabetes mellitus manifests differential effects on the contractile properties of slow and fast skeletal muscles of male Sprague Dawley rats.