Antilipolytic nature of gut GLI, and mode of action of two highly potent intestinal lipolytic species in birds.

Three major lipolytic factors, termed peaks 1, 2 and 3, according to their elution sequence from Biogel P6 columns, have been identified in duck intestinal extracts. The small molecular weight peaks 2 and 3, were even more lipolytically potent on chick adipocytes than pancreatic glucagon; peak 1, called gut GLI, because of its cross-reactivity in a radioimmunoassay for glucagon, modified the lipolytic activity of peak 2 and pancreatic glucagon. It did so by modifying their capacity to stimulate cyclic AMP production. Peaks 2 and 3 exert their lipolytic effects via different intermediary pathways: only peak 2 induced the formation of cyclic AMP. Insulin in birds is devoid of any antilipolytic activity; this fundamental role may be assumed by gut GLI.