Department of Animal Science, Texas A&M University, College Station, TX 77843, USA.
Nu-Tetics AgVentures, Inc., 12247 CR 8390, West Plains, MO 65775, USA.
J Anim Sci. 2021 Aug 1;99(8). doi: 10.1093/jas/skab116.
Chinese hamster ovary cell constructs expressing either the β 1-, β 2- or β 3-adrenergic receptor (AR) were used to determine whether a novel β-AR modulator, lubabegron fumarate (LUB; Experior, Elanco Animal Health) might exert greater potency for a specific β-AR subtype. EC50 values calculated based on cAMP accumulation in dose response curves indicate that LUB is highly selective for the β 3-AR subtype, with an EC50 of 6 × 10-9 M, with no detectible agonistic activity at the β 2-AR. We hypothesized that the accumulation of lipolytic markers would reflect the agonist activity at each of the β-receptor subtypes of the specific ligand; additionally, there would be differences in receptor subtype expression in subcutaneous (s.c.) and intrmuscular (i.m.) adipose tissues. Total RNA was extracted from adipose tissue samples and relative mRNA levels for β 1-, β2-, and β 3-AR were measured using real-time quantitative polymerase chain reaction. Fresh s.c. and i.m. adipose tissue explants were incubated with isoproterenol hydrochloride (ISO; β-AR pan-agonist), dobutamine hydrochloride (DOB; specific β 1-AA), salbutamol sulfate (SAL; specific β 2-AA), ractopamine hydrochloride (RAC), zilpaterol hydrochloride (ZIL), BRL-37344 (specific β 3-agonist), or LUB for 30 min following preincubation with theophylline (inhibitor of phosphodiesterase). Relative mRNA amounts for β 1-, β 2-, and β 3-AR were greater (P < 0.05) in s.c. than in i.m. adipose tissue. The most abundant β-AR mRNA in both adipose tissues was the β 2-AR (P < 0.05), with the β 1- and β 3-AR subtypes being minimally expressed in i.m. adipose tissue. ISO, RH, and ZH stimulated the release of glycerol and nonesterified fatty acid (NEFA) from s.c. adipose tissue, but these β-AR ligands did not alter concentrations of these lipolytic markers in i.m. adipose tissue. LUB did not affect glycerol or NEFA concentrations in s.c. or i.m. adipose tissue, but attenuated (P < 0.05) the accumulation of cAMP mediated by the β 1- and β 2-AR ligands DOB and SAL in s.c. adipose tissue. Collectively, these data indicate that bovine i.m. adipose tissue is less responsive than s.c. adipose tissue to β-adrenergic ligands, especially those that are agonists at the β 1- and β3-receptor subtypes. The minimal mRNA expression of the β 1- and β 3 subtypes in i.m. adipose tissue likely limits the response potential to agonists for these β-AR subtypes.
使用表达 β1-、β2-或β3-肾上腺素能受体（AR）的中国仓鼠卵巢细胞构建体来确定新型β-AR 调节剂富马酸芦巴贝隆（LUB；Experior，Elanco 动物保健）是否可能对特定的β-AR 亚型表现出更大的效力。根据 cAMP 积累的剂量反应曲线计算的 EC50 值表明，LUB 对β3-AR 亚型具有高度选择性，EC50 为 6×10-9 M，在β2-AR 上没有可检测到的激动活性。我们假设脂解标志物的积累将反映特定配体中每个β-受体亚型的激动活性；此外，在皮下（s.c.）和肌肉内（i.m.）脂肪组织中，受体亚型表达会存在差异。从脂肪组织样本中提取总 RNA，并使用实时定量聚合酶链反应测量 β1-、β2-和β3-AR 的相对 mRNA 水平。将新鲜的 s.c. 和 i.m. 脂肪组织外植体与盐酸异丙肾上腺素（ISO；β-AR 泛激动剂）、盐酸多巴酚丁胺（DOB；特定的β1-AA）、硫酸沙丁胺醇（SAL；特定的β2-AA）、盐酸莱克多巴胺（RAC）、盐酸齐帕特罗（ZIL）、BRL-37344（特异性β3-激动剂）或 LUB 一起孵育 30 分钟，然后用茶碱（磷酸二酯酶抑制剂）预孵育。与 i.m. 脂肪组织相比，s.c. 中的 β1-、β2-和 β3-AR 的相对 mRNA 量更大（P<0.05）。两种脂肪组织中最丰富的β-AR mRNA 是β2-AR（P<0.05），而β1-和β3-AR 亚型在 i.m. 脂肪组织中的表达很少。ISO、RH 和 ZH 刺激 s.c. 脂肪组织中甘油和非酯化脂肪酸（NEFA）的释放，但这些β-AR 配体不会改变 i.m. 脂肪组织中这些脂解标志物的浓度。LUB 不会影响 s.c. 或 i.m. 脂肪组织中甘油或 NEFA 的浓度，但会减弱（P<0.05）由 DOB 和 SAL 介导的 cAMP 在 s.c. 脂肪组织中的积累，这两种配体均为β1-和β2-AR 激动剂。这些数据表明，牛 i.m. 脂肪组织对β-肾上腺素能配体的反应不如 s.c. 脂肪组织敏感，尤其是那些对β1-和β3-受体亚型具有激动活性的配体。i.m. 脂肪组织中β1-和β3 亚型的最小 mRNA 表达可能限制了这些β-AR 亚型对激动剂的反应潜力。
