The present study was designed to provide more extensive information on the effects of chronic in vivo β-adrenergic stimulation as produced in two different fashions, one through exercise training and the other through the chronic administration of isoproterenol, on the characteristics of β-adrenergic receptors (β-AR) in rat adipocyte membranes.
1. The chronic administration of isoproterenol (2.5 mg/kg BW sc, daily for 21 days; IPR-treatment) significantly reduced lipolysis induced by noradrenaline in isolated adipocytes. However, exercise training (8 weeks of treadmill running) significantly increased the lipolytic response of adipocytes to noradrenaline.
2. IPR-treatment significantly decreased the percentage of the high affinity state (%R_H) and increased the dissociation constants of the high affinity state (K_H) of β-AR in computer modeling of (-) -noradrenaline competition curves. However, exercise training significantly increased %R_H.
In conclusion, IPR-treatment reduced the lipolytic response of adipocytes to noradrenaline, at least partially, which resulted in the decreased formation of the high affinity state of β-AR. Exercise training may enhance the lipolytic ability of adipocytes to catecholamines through facilitating the formation of the high affinity state of β-AR.

The present study was designed to provide more extensive information on the effects of chronic in vivo β-adrenergic stimulation as produced in two different fashions, one through exercise training and the other through the chronic administration of isoproterenol, on the characteristics of β-adrenergic receptors (β-AR) in rat adipocyte membranes.
1. The chronic administration of isoproterenol (2.5 mg/kg BW sc, daily for 21 days; IPR-treatment) significantly reduced lipolysis induced by noradrenaline in isolated adipocytes. However, exercise training (8 weeks of treadmill running) significantly increased the lipolytic response of adipocytes to noradrenaline.
2. IPR-treatment significantly decreased the percentage of the high affinity state (%R_H) and increased the dissociation constants of the high affinity state (K_H) of β-AR in computer modeling of (-) -noradrenaline competition curves. However, exercise training significantly increased %R_H.
In conclusion, IPR-treatment reduced the lipolytic response of adipocytes to noradrenaline, at least partially, which resulted in the decreased formation of the high affinity state of β-AR. Exercise training may enhance the lipolytic ability of adipocytes to catecholamines through facilitating the formation of the high affinity state of β-AR.