Adaptation to fasting in baboon. II. Regulation of lipolysis early and late in fasting

Regulation of lipolysis by the sympathetic nervous system, basal insulin, and glucagon was studied in fasted baboons. Beta-Adrenergic mechanisms were evaluated by blockade with propranolol after 24, 40, and 65 h of fasting. Inhibition of lipolysis decreased with increasing duration of fasting. Insulin concentrations were markedly reduced by propranolol at all stages of fasting, whereas glucose and glucagon concentrations were unchanged. The roles of insulin and glucagon were evaluated by a 2-h infusion of somatostatin after 18 and 65 h of fasting. At both times, insulin and glucagon concentrations were markedly reduced. At 18 h of fasting but not at 65 h, lipolysis doubled. At both times the plasma glucose concentration fell 15-30%. At 18 h, preventing the decrease in glucose with glucose infusion prevented the increase in lipolysis. These data suggest that a beta-adrenergic mechanism is largely responsible for regulation of lipolysis early in fasting and that insulin, glucagon, and beta-adrenergic mechanisms play no major part in the maintenance of the accelerated lipolysis later in fasting.

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