A ROLE FOR PANCREATIC HORMONES IN THE REGULATION OF AUTUMNAL FAT DEPOSITION OF THE GARDEN WARBLER (SYLVIA BORIN)

Glucagon and insulin were measured by heterologous immunoassays in pla sma samples of 17 garden warblers (Sylvia borin) kept under constant a d libitum or fasting-refeeding conditions during the migratory season from September to May. Plasma levels of key metabolic indicators (gluc ose, triglycerides, cholesterol, and free fatty acids) were measured e very 2 weeks. Measurements of the two hormones concur with the general assumption of a higher glucagon:insulin ratio, indicating a more pron ounced catabolism in birds than in mammals. The concentrations of both hormones varied (insulin: 0.7-7.7 mu IU/ml, n = 66; glucagon: 0.4-4.5 ng/ml, n = 99), but differences between mean values per month were si gnificant only for glucagon. Neither hormone titer correlated with eit her the seasonal or a fasting-refeeding-induced body mass cycle. Howev er, there was a positive correlation between food intake, changes in b ody mass, and plasma triglycerides and insulin; in contrast, there was a negative relationship with the glucagon:insulin ratio. Glucagon sho wed only a small negative relationship to plasma glucose and cholester ol, but correlated directly more closely with plasma free fatty acids. The present data support the fact that glucagon is more lypolytic in birds than in mammals. Pancreatic hormones are suggested to participat e in the regulation of premigratory hyperphagia and hyperlipemia. (C) 1997 Academic Press.