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.