Estimates of fish glucagon by heterologous radioimmunoassay: antibody selection and cross-reactivities

Abstract

Mammalian radioimmunoassay may be used for the measurement of fish glucagon, but the antibody must be chosen carefully. Of the antibodies analysed, 30K (Unger et al., J. clin. Invest. 41, 628–689), K5563 (Novo), 299-221R (Cambridge), and A31 (Milab), 30K and K5563 appear to be the most suitable. No differences were observed between glucagon determination in polyethylenglycol-extracted and non-extracted plasma samples. This finding suggests that large glucagon-related peptides, if they are present in fish plasma, would not alter glucagon measurements, and thus extraction procedures are not necessary. Fish glucagon-like peptides did not interfere appreciably in the assay. In prespawning, naturally fasting adult trout, high glucagon plasma levels (1310.0 ± 161.3 pg/ml) together with very low levels of circulating insulin (2.2 ± 0.4 ng/ml) determined an unusually high G I molar ratio of 1.0.