The effects of the [beta]â‚‚ agonists fenoterol on the contractile and biochemical properties of skeletal muscle

Abstract

The purpose of this study was to determine if long-term administration of the β2 adrenergic agonist, fenoterol, would increase myosin content and peak tetanic tension in skeletal muscle. A group of 26 male grass frogs (Rana pipiens) were size matched and placed into two groups, a drug group (D) and a control group (C). Following a four week feeding and acclimatization period, the D group received an oral dose of fenoterol at a dosage of 2.0mg/kg/day for eight weeks. The C group was given an equal volume (1.5ml) of distilled water. At the end of the eight weeks, the animals were sacrificed and the sartorius muscles were removed. Muscles were electrically stimulated using a series of five tetanizing trains (>90v, 100Hz for 300ms) separated by a 120 sec rest interval and peak tetanic tensions (PPT) were recorded. Muscles were then blotted and weighed. Total protein content of each muscle was computed from nitrogen content using the micro-kjeldahl technique. Gel electrophoresis and densitometry were used to measure myosin content (MTOT) as an indicator of contractile protein content. No significant difference in sartorius weight was seen in the drug versus control group (p<.0709). Additionally, there was no significant difference between groups in the values for total protein (p<.666) or myosin to total protein ration (p<.075). Myosin content was 23.6% greater in the D group (D=11.65mg, C=9.41mg), and peak tetanic tension was 13.9% (D=72.57, C=63.72) greater in the D group compared to controls. MANCOVA showed a statistically significant difference between groups (Wilke's criterion=0.7428, p<.038). These results confirm the ergogenic nature of the β2 agonist, fenoterol, since it does indeed increase myosin content and performance when administered over a prolonged period.