1. Sheep adipose tissue retained responsiveness to catecholamines when maintained in tissue culture for 48 h; both the rate of basal lipolysis and sensitivity to β-agonists were increased after tissue culture. 2. Tissue culture in the presence of growth hormone resulted in an increased maximum response and sensitivity to the β-agonist isoprenaline, but had no effect on basal lipolysis. 3. Tissue culture in the presence of insulin increased the basal rate of lipolysis and increased the ratio of the rate of noradrenaline-stimulated/isoprenaline-stimulated lipolysis, indicating a decrease in the 2-adrenergic effect of noradrenaline. 4. Tissue culture in the presence of growth hormone increased ligand binding to β-adrenergic receptors. 5. Tissue culture in the absence of exogenous hormones increased ligand binding to alpha 2-adrenergic receptors; this was prevented by actinomycin D and partly prevented by insulin. 6. These studies show that both growth hormone and insulin chronically modulate the adrenergic system of sheep adipose tissue; the effects of growth hormone are primarily on the β-adrenergic system, whereas insulin modulates the alpha 2-adrenergic system.
