Effect of streptozotocin-induced diabetes on growth and proteolytic activity of different muscles in rats.

Fibre and non-fibre components and proteolytic activity of fore- and hindlimb muscles with different fibre composition and functions were examined in streptozotocin-induced diabetic rats. From hindlimb, extensor digitorum longus (EDL), medial gastrocnemius (MG) and soleus (SOL) were selected to represent muscles rich in fast oxidative-glycolytic, fast glycolytic and slow oxidative fibres, respectively. The biceps brachii (BB) and extensor carpi radialis longus (ECRL), represented forelimb muscles having similar fibre composition but performing flexor and extensor functions respectively. Among the five muscles studied, all but SOL showed decrease in muscle weight and protein in diabetic rats indicating the atrophy of these muscles. Atrophy was greater in EDL and MG as compared to ECRL and BB. This differential atrophy could be negatively correlated to the percentage of slow oxidative fibres. Despite the loss of fibre mass in diabetic group, elevated fibre protein concentration was observed in BB (flexor) but not in ECRL (extensor). There was a significant reduction in non-fibre protein concentration with markedly enhanced alkaline proteolytic activity in EDL of diabetic rats. Non-protein solid concentration was also increased in EDL and MG. These observations showed that fast muscles are more susceptible to diabetes induced atrophic changes and diabetes affected various muscle components differently in muscles with different fibre composition and functions. Therefore, fibre composition and function of a muscle may be the factors in determining muscle growth in diabetes.

Protein energy ratio as a critical factor in determining growth & glycogen content of muscles in rats.

Effect of protein deficiency, which was produced in rats either by feeding low protein diet (8% protein) ad libitum (PD) or by restricting the amount of diet containing 15 per cent protein (protein calorie deficiency; PCD) on the growth in terms of muscle weight, length, cross-sectional area, protein and glycogen content was studied in extensor digitorum longus (EDL), medial gastrocnemius (MG) and plantaris (PL) muscles in rat. Because of decreased total calorie intake, PCD group exhibited higher value for protein/total calorie consumption. Excepting glycogen concentration, the retardation of growth in terms of all parameters studied was less in the PCD group. Glycogen concentration (mg/g muscle weight) in the PCD group was 3.0 +/- 0.3 in EDL and 2.6 +/- 0.3 in PL, whereas the values in PD group were 1.0 +/- 0.1 in EDL and 1.1 +/- 0.2 in PL respectively. This glycogen sparing effect was not evident in MG of PCD group possibly due to the greater number of glycolytic fibres. It is suggested that lesser retardation of growth of muscles and glycogen sparing effect in PCD group, could be due to altered metabolic changes resulting in enhanced gluconeogenesis.

Fatigue and contractile responses of rat hindlimb muscles following excessive dexamethasone administration.

Muscle weight, protein content and contractile performance (tetanic tension, fatigue and recovery) of extensor digitorum longus and soleus were investigated in rat following systemic administration of Dexamethasone (DX), 5 mg/kg/day for ten days. These animals showed marked reduction in food intake during the course of DX treatment. As a control, a group of food restricted (FR) rats receiving equal amount of food consumed by the DX treated rats was also studied along with the saline control group, to differentiate the effect of DX on muscle from that of dietary deficiency. There was a greater degree of atrophy (reduced muscle mass and protein content) of extensor digitorum longus in DX treated rats as compared to that of the FR rats. In-situ isometric tetanic tension per gram of muscle and per unit weight of protein was similar in both the muscles in the DX treated and the FR rats. There was increased fatiguability with reduced post fatigue recovery in both the muscles of DX treated rats as compared to the FR rats. The results indicate that besides atrophy of fast twitch muscles, DX increases the fatiguability and decreases the postfatigue recovery in both fast and slow muscles.