PSIV-14 - Evidence for functional G-coupled protein receptors 43 and 120 in subcutaneous and intramuscular adipose tissue of Angus crossbred steers

We conducted experiments to demonstrate functional G-coupled protein receptor 43 (GPR43) and GPR120 in bovine intramuscular (i.m.) and subcutaneous (s.c.) adipose tissues. We hypothesized that media volatile fatty acids and long-chain fatty acids would affect cAMP concentrations differently in i.m. and s.c. adipose tissue, which would be dependent on GPR receptor populations in the adipose tissue sites. Fresh s.c. and i.m. adipose tissue from the 5^th-8^th longissimus thoracic rib muscle section of Angus crossbred steers (approximately 20 mo of age) was transferred immediately to 6-well culture plates containing 3 mL of KHB/Hepes/5 mM glucose. Samples were pre-incubated with 0.5 mM theophylline plus 10 μM forskolin for 30 min, after which increasing concentrations of acetate or propionate (0, 10^-3, 10^-2.3, and 10^-3 M) in the absence or presence of 100 μM oleic acid (18:1 n-9) or 100 µM palmitic acid (16:0) were added to the incubation media. Acetate had no effect on forskolin-stimulated cAMP production in s.c. adipose tissue but decreased cAMP in i.m. adipose tissue (P < 0.05); this indicates a functional GPR43 receptor in i.m. adipose tissue. The combination of 10^-2 M acetate and oleic acid decrease cAMP production in s.c. adipose tissue, consistent with GPR120 receptor activity, but oleic acid and palmitic acid attenuated the depression of cAMP production caused by acetate in i.m. adipose tissue. Palmitic acid depressed cAMP production in s.c. adipose tissue, and increased cAMP production in i.m. adipose tissue (P < 0.05). Propionate had no effect on cAMP production in s.c. or i.m. adipose tissue. These results provide evidence for functional GPR43 receptors in i.m. adipose tissue and GPR120 receptors in s.c. adipose tissue, both of which would suppress lipolysis. Further research may allow producers to increase marbling with exacerbating carcass fatness through pharmacological or dietary strategies.