Variations in pancreatic glucoregulatory hormones in birds (1101.1)

Abstract

Plasma glucose concentrations (PGlu) in birds are naturally 1.5‐2 times greater on average than mammals of similar body mass. However, mechanisms regulating variations in PGlu across species with similar body mass are poorly understood. One theory is that the relative expression of the pancreatic glucoregulatory hormones insulin (lowers PGlu) and glucagon (increases PGlu) differs across species. However, evidence suggests many avian species are resistant to the glucose‐lowering effects of insulin. Therefore, the purpose of this pilot study was to correlate PGlu with pancreatic insulin and glucagon concentrations across diverse species of birds (pigeon, mourning dove, mallard duck, northern pintail duck, and Gambel’s quail). It was hypothesized that, similar to mammals, PGlu would be positively correlated with glucagon and negatively correlated with insulin expression in the pancreas. PGlu was measured using a commercially available kit. Pancreata were isolated, embedded in OCT compound and 12 micron cryosections were collected onto glass microscope slides. Tissue sections were then immunostained for insulin and glucagon. Commercially available ELISAs were used to verify immunohistochemical observations. Consistent with a negative relationship between PGlu and body mass for birds, mourning doves have the highest PGlu (24.02 mM/L) whereas mallard ducks have the lowest PGlu (11.14 mM/L). Insulin was not significantly correlated with variations in PGlu (Spearman coefficient 0.035; p=0.864), supporting prior observations that many species are resistant to the glucose‐lowering effects of insulin. Moreover, immunohistochemical data from doves and quail show higher glucagon expression as compared to insulin, which may contribute to their naturally high PGlu.