Effect of α-adrenergic stimulation and its blockade on glucose turnover in man

Epinephrine (50 ng/kg^-1/min^-1) was infused for 120 min in seven normal volunteers alone (combined α- and β-adrenergic stimulation), with propranolol (α-adrenergic stimulation), and with propranolol plus phentolamine (α-adrenergic blockade superimposed on α-adrenergic stimulation). During α-adrenergic stimulation, plasma glucose and glucose production increased 32 and 42% less, respectively, than during infusion of epinephrine alone, whereas glucose clearance was suppressed comparably. Plasma insulin decreased during α-adrenergic stimulation but increase during infusion of epinephrine plus propranolol than during infusion of epinephrine alone. When α-adrenergic blockade was superimposed on α-adrenergic stimulation, the increases in plasma glucose and glucose production as well as the decreases in plasma insulin and glucose clearance observed during α-adrenergic stimulation were virtually abolished, whereas plasma epinephrine levels were unaltered. These results indicated that in man epinephrine can cause hyperglycemia via both α- and β-adrenergic stimulation of glucose production and suppression of glucose clearance, either directly or indirectly. α-Adrenergic effects on glucose production and clearance may be mediated by inhibition of insulin secretion.