Thyroid Hormone and Growth Hormone Regulation of Broiler Adipocyte Lipolysis

Broiler adipocytes in culture were utilized 1) to determine acute and chronic effects of triiodothyronine (T3) and growth hormone (GH) on lipolysis; and 2) to determine whether T3 and GH act synergistically to increase lipolysis. Short-term effects of T3 and GH on lipolysis were determined by measuring glycerol release from adipocytes incubated for 1 h with T3 or GH and glucagon (GLU). To investigate long-term effects, adipocytes were cultured for 24 h with T3, GH, or a combination of T3 and GH before removal of hormones by washing and assessment of lipolysis. Basal and GLU-stimulated lipolysis were not altered by short-term (1 h) incubation of adipocytes with T3 or GH. Pretreatment of adipocytes with T3 for 24 h increased (P < .05) basal lipolysis and lipolysis in the presence of low (.3 to 1.5 ng/mL) doses of GLU. Preincubation of adipocytes with GH for 24 h decreased (P < .05) glycerol release in response to maximal stimulatory doses (3 to 10 ng/mL) of GLU and increased (P < .05) glycerol release in response to .3 ng GLU/mL. Long-term pretreatment of adipocytes with a combination of T3 and GH produced a similar increase in lipolysis with .3 ng GLU/mL as pretreatment with either T3 or GH alone. Thus, T3 and GH did not act synergistically to increase lipolysis from broiler adipocytes.