# Temporal Pattern of cAMP Concentrations and α-Actin mRNA Expression in Skeletal Muscle of Cimaterol-Fed Rats

• Kim, Y.S. (Department of Animal Sciences, University of Hawaii at Manoa) ;
• Duguies, M.V. (College of Agriculture and Life Sciences, University of Guam) ;
• Kim, Y.H. (Department of Animal Sciences, University of Hawaii at Manoa) ;
• Vincent, D.L. (Department of Animal Sciences, University of Hawaii at Manoa)
• Received : 1996.08.22
• Accepted : 1997.07.15
• Published : 1997.10.01
• 42 2

#### Abstract

Twenty four female Sprague-Dawley rats weighing about 190 g were used to examine changes in muscle cAMP concentrations and steady-state levels of skeletal muscle ${\alpha}$-actin mRNA during chronic administration of cimaterol, a ${\beta}$-adrenergic agonist. Cimaterol was mixed in a powdered rat diet at 10 mg/kg diet. At 3 and 21 days after the start of treatment, skeletal muscle and heart samples were collected for the measurement of cAMP concentrations and skeletal muscle ${\alpha}$-actin mRNA levels. Cimaterol increased (p < 0.01) body weight gain gradually during the first seven days of the trial period, but not thereafter. Most skeletal muscle weights and the ratio of muscle weight to body weight were increased (p < 0.05) by cimaterol treatment both at 3 and 21 days. Heart weight was also increased (p < 0.05) by cimaterol treatment at 3 and 21 days, but the ratio of heart weight to body weight was increased (p < 0.05) only at 3 day. Cimaterol decreased (p < 0.05) cAMP concentration of gastrocnemius muscle at both 3 and 21 days after treatment. However, cimaterol tended (p = 0.07) to increase cAMP concentration at 3 days in the heart. Cimaterol tended (p = 0.08) to increase the steady-state level of ${\alpha}$-actin mRNA by 60% in gastrocnemius muscle at 3 days but had no effect at 21 days. The results indicate that the pattern of hypertrophic response to chronic dietary administration of cimaterol is different between cardiac and skeletal muscle. In skeletal muscles it appears that the hypertrophy induced by cimaterol is partly due to stimulated myofibrillar protein synthesis at a pre-translational level.

#### Keywords

Beta-Adrenergic Agonist;Cimaterol;cAMP;Actin mRNA;Skeletal Muscle;Heart