Metabolic responses of perfused rat livers to alpha- and beta-adrenergic agonists, glucagon and cyclic AMP

1. The mechanism of action of glucagon and epinephrine was studied in perfused rat livers. Hormone-induced transitions from one metabolic steady state to another were followed in a non-recirculating perfusion system. Glucose and lactate production rates, oxygen uptake and K+ redistribution were measured. 2. Glucagon (3 nM), cyclic AMP (0.2 mM) and epinephrine (0.5 muM) had similar effects on K+ concentrations in the perfusate. Glycogenolysis responded more rapidly and O2 uptake was enhanced to a larger extent with epinephrine than with the other agents. alpha- and beta-receptor responses were differentiated by the use of phenylephrine (0.5 muM), isoproterenol (0.5 muM) and adrenergic blocking agents (phentolamine and beta-blocker Ro 3-4787 at 0.1 mM). 3. alpha-receptors mediated an activation of glucose production that was very rapid and was paralleled by a transient decrease of K+ concentrations in the effluent from the liver, lactate production rose gradually. Respiration was also enhanced, but fell again as lactate production increased. 4. beta-receptor stimulation was followed by an increase of glucose production that was less drastic and was paralleled by a K+ release, lactate production and respiration were only slightly enhanced. beta stimulation and glucagon both resulted in an inhibition of the alpha-adrenergic effect on lactate release and simultaneously increased O2 uptake. 5. We concluded that in perfused rat livers alpha- as well as beta-adrenergic receptor stimulation resulted in an activation of glycogenolysis, possibly by two different mechanisms.

Nonsuppressible insulin-like activity in human serum. 3. Differentiation of two distinct molecules with nonsuppressible ILA

Total nonsuppressible insulin-like activity (ILA) of human plasma (measured by the adipose tissue assay) results from the additive effects of at least two distinct components. They differ in molecular size, solubility in acid-ethanol, and in thermostability. More than 90% of nonsuppressible ILA of human plasma is insoluble in acid-ethanol. Its molecular size of 100,000-150,000 remains unchanged by treatment with acid-ethanol, 5 M acetic acid-0.15 M NaCl, urea, and EDTA. It is inactivated by heat. Approximately 5% of total nonsuppressible serum ILA is soluble in acid-ethanol. The molecular weight is 6000-10,000 after partial purification on Sepadex G-75 (acetic acid-NaCl). This molecule is thermostabile for 3 hr at 80 degrees C. When the acid-ethanol soluble molecule with nonsuppressible ILA is chromatographed on Sephadex G-100 at neutral pH, it is eluted in a broad peak corresponding to a molecular weight of approximately 50,000-70,000. When rechromatographed on Sephadex G-75 (acetic acid-NaCl) its mol wt is irreversibly converted from 70,000 to 6000. Most of the insulin-like activity retained on Dowex-50 ("bound insulin") is eluted off Sephadex G-75 (acetic acid-NaCl) at the same column volume as the small molecular weight nonsuppressible ILA. The latter molecule is retained on Dowex-50, whereas big molecular weight nonsuppressible ILA is not.