Interactions of Glucagon and Related Peptides with Chicken Adipose Tissue

Abstract

The effect of glucagon, Vasoactive Intestinal Polypeptide (VIP), secretin and gut glucagon on the cyclic adenosine 3'5' monophosphate (cAMP) level, and on the specific binding of these ¹²⁵I-peptides to the adipocyte plasma membrane was measured in chicken adipocytes and compared to the results obtained in rat adipocytes. The displacement of ¹²⁵I-glucagon from its specific sites was observed with about the same concentration of unlabeled hormone in fat cell plasma membranes of both species. However, the rise in cAMP induced by glucagon was much higher in chicken than in rat adipocytes. In chicken fat cells, unlike rat fat cells, the cAMP accumulation elicited by glucagon was maintained during at least 60 min even in the absence of theophylline. Theophylline at 1-10 mM potentiated the glucagon-stimulated cAMP levels in rat fat cells, but had only a slight effect, if any, in chicken adipocytes. Porcine VIP, secretin or gut glucagon exerted no detectable action on the cAMP level of chicken adipocytes. The lack of cAMP accumulation was in good agreement with the absence of binding of ¹²⁵I-VIP and ^l25I-secretin by chicken plasma membranes. These findings suggest that: 1) the difference of glucagon effect in rat and chicken fat cells results from variations in the rate of degradation of cAMP rather than from differences in the specific binding of glucagon between the two species; 2) the use of chicken fat cells is suitable to discriminate between glucagon and structurally related peptides from mammals.

Key words

Chicken - Adipocyte - Glucagon - Gut Glucagon - Vasoactive Intestinal Polypeptide - Secretin - Cyclic AMP - Binding Site - Receptors - Hormonal Action

1 Permanent address: Institut National de la Santé et de la Recherche Médicale, Groupe de Recherches sur les Hormones Polypeptidiques et la Physiopathologie Endocrinienne U 145, Faculté de Médecine (Pasteur), Chemin de Vallombrose, F-06100 Nice, France.