A limited number of ss-adrenergic agonists (ss-AA) are currently used for redirecting dietary energy from adipose tissue accretion towards muscle growth. At the end of typical feedlot finishing, cattle have depressed insulin sensitivity, similar to type II diabetes in humans. The objective of this study was to compare the effects of a known ?v3-AA (BRL 37344) to a novel ss-AA (Experior) on muscle metabolism in vitro. We hypothesized that Experior would attenuate insulin insensitivity by promoting glucose metabolism in muscle. The M. longissimus lumborum (LL) was removed from the 9th to 11th rib from four steers. From the LL samples, muscle strips were dissected parallel to muscle fiber orientation. The conversion of glucose to glycogen, COv2, and lactate was tested in muscle strips incubated for 90 min with 50 uM Experior, 50 uM BRL 37344, or no ?-AA (Control), and different insulin concentrations. Incubation time was established by a preliminary experiment that determined the effect of different incubation times (30 min, 60 min, 90 min) on glycogen, COv2, and lactate production. There were no (P > 0.05) insulin concentration x treatment effects, insulin concentration effects, and no significant effect of treatment on lactate production. There was a significant treatment effect of conversion of glucose to glycogen (P < 0.001) and COv2 (P = 0.018). BRL 37344 caused 62% lower glycogen production compared to Control samples, and 50% lower glycogen production compared to Experior samples. Control samples produced 4.3 nmol/100 mg.90 min, Experior samples produced 3.1 nmol/100 mg.90 min glycogen, while BRL 37344 samples produced 1.6 nmol/100 mg.90 min. BRL 37344 elicited 23% more COv2 than Experior, and 41% more COv2 than Control samples. Control samples produced 171.3 nmol/100 mg.90 min COv2, Experior samples produced 222.9 nmol/100 mg.90 min COv2, while BRL 37344 samples produced 292.6 nmol/100 mg.90 min COv2. Experior did not have a consistent effect on glycogen or COv2 production. We discovered the presence of ssv3- AR in muscle, since there was a distinct response of the muscle strips to BRL 37344. The relative insensitivity of bovine muscle to insulin is consistent with insulin resistance observed in feedlot cattle.
