INSULIN, GLUCAGON AND CATECHOLAMINE INTERACTIONS IN AVIAN LIVER EXPLANTS

1. A mechanical tissue chopper was used to obtain liver explants (35 75 mg) from 2- to 3-week-old chickens to determine both tissue sensitivity and metabolic effects of isoproterenol, avian insulin and glucagon. 2. Avian insulin had no effect on lipogenesis; however, lipogenesis was decreased by dibutyryl cyclic AMP. Insulin did not overcome a decrease in lipogenesis caused by catecholamines. Therefore, this control mechanism is not modulated by insulin. 3. Preincubation in the presence of glucagon decreased in vitro lipogenesis. Preincubation in the presence of a 19 29 amino acid construct that approximated the radioimmune site for glucagon did not result in a similar effect. Therefore, this site does not relate to the biopotency of the hormone. 4. A previously noted catecholamine induced decrease in in vitro lipogenesis was verified, showing that points of in vitro regulation are under phosphorylation-dephosphorylation control. 5. Preincubation of slices (I hr) with propranolol blocked the inhibition of lipogenesis caused by alpha and beta-adrenergic agonists (arterenol or isoproterenol) during a subsequent 2-hr incubation. 6. Preincubation of slices with either of these agonists decreased lipogenesis even following an extensive washout. 7. Inhibition could be overcome with propranolol, a beta-adrenergic antagonist.