Zilpaterol hydrochloride alters abundance of β-adrenergic receptors in bovine muscle cells but has little effect on de novo fatty acid biosynthesis in bovine subcutaneous adipose tissue explants

We predicted that zilpaterol hydrochloride (ZH), a beta-adrenergic receptor (AR) agonist, would depress mRNA and protein abundance of beta-AR in bovine satellite cells. We also predicted that ZH would decrease total lipid synthesis in bovine adipose tissue. Bovine satellite cells isolated from the semimembranosus muscle were plated on tissue culture plates coated with reduced growth factor matrigel or collagen. Real-time quantitative PCR was used to measure specific gene expression after 48 h of ZH exposure in proliferating satellite cells and fused myoblasts. There was no effect of ZH dose on [H-3] thymidine incorporation into DNA in proliferating myoblasts. Zilpaterol hydrochloride at 1 mu M decreased (P < 0.05) beta 1-AR mRNA, and 0.01 and 1 mu M ZH decreased (P < 0.05) beta 2-AR and beta 3-AR mRNA in myoblasts. The expression of IGF-I mRNA tended to increase (P = 0.07) with 1 mu M ZH. There was no effect (P > 0.10) of ZH on the beta-AR or IGF-I gene expression in fused myotube cultures at 192 h or on fusion percentage. The beta 2-AR antagonist ICI-118, 551 at 0.1 mu M attenuated (P < 0.05) the effect of 0.1 mu M ZH to reduce expression of beta 1- and beta 2-AR mRNA. The combination of 0.01 mu M ZH and 0.1 mu M ICI-118, 551 caused an increase (P < 0.05) in beta 1-AR gene expression. There was no effect (P > 0.10) of ICI-118, 551 or ZH on beta 3-AR or IGF-I. Western blot analysis revealed that the protein content of beta 2-AR in ZH-treated myotube cultures decreased (P < 0.05) relative to control. Total lipid synthesis from acetate was increased by ZH in bovine subcutaneous adipose tissue explants in the absence of theophylline but was decreased by ZH when theophylline was included in the incubation medium. These data indicate that ZH alters mRNA and protein concentrations of beta-AR in satellite cell cultures, which in turn could affect responsiveness of cells to prolonged ZH exposure in vivo. Similar to other beta-adrenergic agonists, ZH had only modest effects on lipid metabolism in adipose tissue explants.