Heat Stress and Betaine Affect Lipolysis in Pig Adipose Tissue Explants

Heat stress (HS) is an environmental variable challenging pig production worldwide. It may alter carcass composition by increasing fat deposition but the mechanisms are poorly understood. Betaine is a metabolic modifier able to decrease carcass fat in pigs, but the effects of betaine on lipolysis under high temperatures are not known. Our goal was to determine a potential effect of betaine on lipolysis in the fat tissue of Iberian pigs under thermoneutral (TN) or HS conditions. Eight pigs (89 kg BW) were used to obtain explants from dorsal subcutaneous adipose tissue. Explants were cultivated under TN (37 °C) or HS conditions (41.5 °C) for 1.5 h to study direct effects of HS on acute lipolysis. Treatments included control and betaine addition (200 µM). Indirect effects of HS were examined using the culture medium amended with 1 μM isoproterenol ±10 nM insulin in the presence or absence of betaine and HS. Media glycerol was measured at the end of the incubations as a proxy of lipolysis. HS decreased basal lipolysis (-47%; p < 0.001) but increased isoproterenol-stimulated (a β-agonist) lipolysis (+31%; p < 0.01). Betaine increased non-stimulated lipolysis both under TN and HS conditions (73%; p < 0.001). As expected, isoproterenol augmented lipolysis both in TN (2714%; p < 0.001) and HS (3589%; p < 0.001) conditions. The addition of insulin to lipolysis-stimulated explants analogously diminished glycerol release in TN (-39%; p < 0.001) and HS (-50%; p < 0.001) conditions. In conclusion, HS reduced non-stimulated lipolysis in Iberian pigs in line with increased adipose tissue accretion, while betaine partly increased lipolysis, counteracting the effects of HS. Betaine supplementation could be a strategy to counteract HS-induced fattening in pigs.